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Short description: Natural process by which life arises from non-living matter
The earliest known life forms are putative fossilized microorganisms, found in hydrothermal vent precipitates, that may have lived as early as 4.28 Gya (billion years ago), relatively soon after the formation of the oceans 4.41 Gya, and not long after the formation of the Earth 4.54 Gya.[1][2]

In biology, abiogenesis or the origin of life[3][4][5] is the natural process by which life has arisen from non-living matter, such as simple organic compounds.[6][4][7][8] While the details of this process are still unknown, the prevailing scientific hypothesis is that the transition from non-living to living entities was not a single event, but an evolutionary process of increasing complexity that involved molecular self-replication, self-assembly, autocatalysis, and the emergence of cell membranes.[9][10][11] Although the occurrence of abiogenesis is uncontroversial among scientists, its possible mechanisms are poorly understood. There are several principles and hypotheses for how abiogenesis could have occurred.[12]

The study of abiogenesis aims to determine how pre-life chemical reactions gave rise to life under conditions strikingly different from those on Earth today.[13] It primarily uses tools from biology, chemistry, and geophysics,[14] with more recent approaches attempting a synthesis of all three:[15] more specifically, astrobiology, biochemistry, biophysics, geochemistry, molecular biology, oceanography and paleontology. Life functions through the specialized chemistry of carbon and water, and builds largely upon four key families of chemicals: lipids (cell membranes), carbohydrates (sugars, cellulose), amino acids (protein metabolism), and nucleic acids (DNA and RNA). Any successful theory of abiogenesis must explain the origins and interactions of these classes of molecules.[16] Many approaches to abiogenesis investigate how self-replicating molecules, or their components, came into existence. Researchers generally think that current life descends from an RNA world,[17] although other self-replicating molecules may have preceded RNA.[18][19]

The classic 1952 Miller–Urey experiment and similar research demonstrated that most amino acids, the chemical constituents of the proteins used in all living organisms, can be synthesized from inorganic compounds under conditions intended to replicate those of the early Earth. Various external sources of energy may have triggered these reactions, including lightning and radiation. Other approaches ("metabolism-first" hypotheses) focus on understanding how catalysis in chemical systems on the early Earth might have provided the precursor molecules necessary for self-replication.[20]

Earth remains the only place in the universe known to harbour life,[21][22] and fossil evidence from the Earth informs most studies of abiogenesis. The age of the Earth is 4.54 Gy (billion years);[23][24][25] the earliest undisputed evidence of life on Earth dates from at least 3.5 Gya (Gy ago),[26][27][28] and possibly as early as the Eoarchean Era (3.6–4.0 Gya). In 2017, possible evidence of early life on land was found in 3.48 Gyo (Gy old) geyserite and other related mineral deposits (often found around hot springs and geysers) uncovered in the Pilbara Craton of Western Australia.[29][30][31][32] Other discoveries suggest that life may have appeared on Earth even earlier. (As of 2017), microfossils (fossilised microorganisms) within hydrothermal-vent precipitates dated 3.77 to 4.28 Gya in rocks in Quebec may harbour the oldest record of life on Earth, soon after ocean formation 4.4 Gya during the Hadean Eon.[1][2][33][34][35]

The NASA strategy on abiogenesis attempts to identify interactions, intermediary structures and functions, energy sources, and environmental factors that contributed to the diversity, selection, and replication of evolvable macromolecular systems,[36] and to map the chemical landscape of potential primordial informational polymers. The advent of polymers that could replicate, store genetic information, and exhibit properties subject to selection likely was a critical step in the emergence of prebiotic chemical evolution.[36]

Definition of life

As many as 123 definitions of life have been compiled.[37] The definition of life is somewhat disagreed upon by biology textbooks. James Gould writes that "most dictionaries define life as the property that distinguishes the living from the dead, and define dead as being deprived of life. These singularly circular and unsatisfactory definitions give us no clue to what we have in common with protozoans and plants."[38] Neil Campbell and Jane Reece state that "the phenomenon we call life defies a simple, one-sentence definition."[39] Books on the origin of life do not agree either. John Casti gives a single-sentence definition: "an entity is considered to be 'alive' if it has the capacity to carry out three basic functional activities: metabolism, self-repair, and replication".[40] In contrast, Dirk Schulze-Makuch and Louis Irwin devote the entire first chapter of their book to discussing the definition of life.[41] NASA defines life as "a self-sustaining chemical system capable of Darwinian evolution."[42][43][44]

Early universe and Earth

Short description: Universe events since the Big Bang 13.8 billion years ago

Early universe with first stars

Soon after the Big Bang, which occurred roughly 14 Gya, the only chemical elements present in the universe were hydrogen, helium, and lithium, the three lightest atoms in the periodic table. These elements gradually came together to form stars. These early stars were massive and short-lived, producing all the heavier elements through stellar nucleosynthesis. Carbon, currently the fourth most abundant chemical element in the universe (after hydrogen, helium and oxygen), was formed mainly in white dwarf stars, particularly those bigger than two solar masses.[45][46]

As these stars reached the end of their lifecycles, they ejected these heavier elements, among them carbon and oxygen, throughout the universe. These heavier elements allowed for the formation of new objects, including rocky planets and other bodies.[47]

According to the nebular hypothesis, the formation and evolution of the Solar System began 4.6 Gya with the gravitational collapse of a small part of a giant molecular cloud.[48] Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed.

Emergence of Earth

The Hadean Earth was at first inhospitable to any living organisms. During its formation, the Earth lost a significant part of its initial mass, and consequentially lacked the gravity to hold molecular hydrogen and the bulk of the original inert gases.[49] The atmosphere consisted largely of water vapor, nitrogen, and carbon dioxide, with smaller amounts of carbon monoxide, hydrogen, and sulfur compounds.[50] The solution of carbon dioxide in water is thought to have made the seas slightly acidic, giving them a pH of about 5.5.[51] The Hadean atmosphere has been characterized as a "gigantic, productive outdoor chemical laboratory,"[52] similar to volcanic gases today which still support some abiotic chemistry.[52]

Oceans may have appeared as soon as 200 My (million years) after the Earth formed, in a hot, 100 C, reducing environment, as the pH of 5.8 rose rapidly towards neutral.[53] This scenario has found support from the dating of 4.404 Gya zircon crystals from metamorphosed quartzite of Mount Narryer in Western Australia, which provide evidence that oceans and continental crust existed within 150 Ma (million years) of Earth's formation.[54] Despite the likely increased volcanism and existence of many smaller tectonic "platelets," it has been suggested that between 4.4 and 4.3 Gya, the Earth was a water world, with little if any continental crust, an extremely turbulent atmosphere, and a hydrosphere subject to intense ultraviolet (UV) light from a T Tauri stage Sun, from cosmic radiation, and from continued bolide (asteroid and comet) impacts.[55] Internal heating as a result of gravitational sorting between the core and the mantle would have caused a great deal of mantle convection, with the probable result of many more smaller and more active tectonic plates than now exist.

The hypothesis for the Late Heavy Bombardment posits that the Hadean environment between 4.28[1][2] and 3.8 Gya would have been highly hazardous to modern life. Following the Nice model, changes in the orbits of the giant planets may have bombarded the Earth with asteroids and comets that pockmarked the Moon and inner planets.[56] Frequent collisions with objects up to 500 km in diameter would sterilize the planet's surface and vaporize the oceans within a few months of impact. Hot steam and rock vapor formed high altitude clouds that would completely cover the planet,[52] making photosynthesis unviable. Rains would slowly have drawn down the height of the clouds, returning the oceans to their original depth only 3,000 y after the impact event.[57] Impacts before 3.5 Gya would have brought quantities of organic material comparable to those produced by terrestrial sources.[58][59] The periods between such devastating events give time windows for the possible origin of life in early environments. If the deep marine hydrothermal setting was the site for the origin of life, then abiogenesis could have happened as early as 4.0-4.2 Gya. If the site was at the surface of the Earth, abiogenesis could have occurred only between 3.7 and 4.0 Gya.[60] However, new lunar surveys and samples have led scientists, including an architect of the Nice model, to deemphasize the Late Heavy Bombardment.[61]

If life evolved deeper than ten meters, it would have been shielded from both late impacts and high levels of UV radiation from the T Tauri stage Sun. Simulations of geothermically heated oceanic crust yield far more organic compounds than those found in the Miller–Urey experiments. In the deep hydrothermal vents, Everett Shock has found "there is an enormous thermodynamic drive to form organic compounds, as seawater and hydrothermal fluids, which are far from equilibrium, mix and move towards a more stable state."[62] Shock found that the available energy is maximized at 100–150 °C, precisely the temperatures at which the hyperthermophilic bacteria and thermoacidophilic archaea have been found living. These organisms are placed at the base of the phylogenetic tree of life, closest to the last Universal Common Ancestor (LUCA).[63]

Earliest evidence of life: palaeontology

Precambrian stromatolites in the Siyeh Formation, Glacier National Park. A 2002 study suggested a date of 3.5 Gya (3.5 billion year old), placing them among the earliest life-forms.
Main page: Biology:Earliest known life forms

The earliest known life on Earth existed more than 3.5 Gya (billion years ago),[26][27][28] during the Eoarchean Era when sufficient crust had solidified following the molten Hadean Eon. The earliest physical evidence so far found consists of microfossils in the Nuvvuagittuq Greenstone Belt of Northern Quebec, in banded iron formation rocks at least 3.77 and possibly 4.28 Gya.[1][64] This finding suggested life developed very soon after oceans formed. The structure of the microbes was similar to bacteria found near hydrothermal vents in the modern era, supporting the view that abiogenesis began near hydrothermal vents.[34][1]

Stromatolites in Shark Bay.

Biogenic graphite has been found in 3.7 Gyo metasedimentary rocks from southwestern Greenland [65] and in microbial mat fossils from 3.49 Gyo Western Australian sandstone.[66][67] Evidence of early life in rocks from Akilia Island, near the Isua supracrustal belt in southwestern Greenland, dating to 3.7 Gya, have shown biogenic carbon isotopes.[68][69] In other parts of the Isua supracrustal belt, graphite inclusions trapped within garnet crystals are connected to the other elements of life: oxygen, nitrogen, and possibly phosphorus in the form of phosphate, providing further evidence for life 3.7 Gya.[70] At Strelley Pool, in the Pilbara region of Western Australia, compelling evidence of early life was found in pyrite-bearing sandstone in a fossilized beach, with rounded tubular cells that oxidized sulfur by photosynthesis in the absence of oxygen.[71][72][73] Work on zircons from Western Australia in 2015 suggested that life likely existed on Earth at least 4.1 Gya.[74][75][76]

In 2019 Raphael Baumgartner and colleagues investigated rocks in the Pilbara region of Western Australia. The Dresser Formation is the oldest, with rocks 3.48 billion years old; it appears to contain layered structures called stromatolites.[77] These stromatolites lie within undeformed hydrothermal-sedimentary strata, and have textural features indicative of biogenic origins. In 2017 Tara Djokic and her team showed that parts of the Dresser formation preserve hot springs on land, but other regions seem to have been shallow seas.[78]

Biology, the product of abiogenesis

Biochemical life processes


Albert Lehninger stated around 1970 that fermentation, including glycolysis, was a suitable primitive energy source for the origin of life, arguing that "Since living organisms probably first arose in an atmosphere lacking oxygen, anaerobic fermentation is the simplest and most primitive type of biological mechanism for obtaining energy from nutrient molecules."[79]


Chemiosmotic coupling mitochondrion

Instead of fermentation, Peter Mitchell proposed chemiosmosis, ubiquitous in life, as the first system of energy conversion.[80][81]

ATP synthase
ATP synthase uses the chemiosmotic proton gradient to power ATP synthesis through oxidative phosphorylation.

The mechanism of ATP synthesis involves a closed membrane in which the ATP synthase is embedded. The ATP is synthesized by the F1 subunit of ATP synthase by the binding change mechanism discovered by Paul Boyer. The energy required to release formed strongly-bound ATP has its origin in protons that move across the membrane. These protons have been set across the membrane during respiration or photosynthesis.

The RNA world

Main page: Biology:RNA world

The RNA world hypothesis describes an early Earth with self-replicating and catalytic RNA but no DNA or proteins.[82] It is widely accepted that current life on Earth descends from an RNA world,[17][83][84] although RNA-based life may not have been the first to exist.[18][19]

RNA is central to the translation process; that small RNAs can catalyze all of the chemical groups and information transfers required for life;[19][85] that RNA both expresses and maintains genetic information in modern organisms; and that the chemical components of RNA are easily synthesized under the conditions that approximated the early Earth. The structure of the ribozyme has been called the "smoking gun", with a central core of RNA and no amino acid side chains within 18 Å of the active site that catalyzes peptide bond formation.[18][86]

The concept of the RNA world was first proposed in 1962 by Alexander Rich,[87] and the term was coined by Walter Gilbert in 1986.[19][88] There were initial difficulties in the explanation of the abiotic synthesis of the nucleotides cytosine and uracil.[89] Subsequent research has shown possible routes of synthesis; for example, formamide produces all four ribonucleotides and other biological molecules when warmed in the presence of various terrestrial minerals.[90][91]

RNA replicase can function as both code and catalyst for further RNA replication. Jack Szostak has shown that certain catalytic RNAs can join smaller RNA sequences together, creating the potential for self-replication. The RNA replication systems, which include two ribozymes that catalyze each other's synthesis, showed a doubling time of the product of about one hour, and were subject to natural selection under the conditions that existed in the experiment.[92][93][18] If such conditions were present on early Earth, then Darwinian natural selection would favor the proliferation of such autocatalytic sets, to which further functionalities could be added.[94][95][96]

Stan Palasek suggested that self-assembly of ribonucleic acid (RNA) molecules can occur spontaneously due to physical factors in hydrothermal vents.[97] Virus self-assembly within host cells has implications for the study of the origin of life,[98] as it lends further credence to the hypothesis that life could have started as self-assembling organic molecules.[99][100] In 2021, it was reported that a preliminary form of tRNA could have been such a replicator molecule.[101][102]

Phylogeny and LUCA

A cladogram placing other extreme hyperthermophiles alongside the LUCA at the base of the phylogenetic tree of life

Starting with the work of Carl Woese, molecular studies have placed the last universal common ancestor (LUCA) between Bacteria and a clade formed by Archaea and Eukaryota in the phylogenetic tree of life.[103][104] A minority of studies have placed the LUCA in Bacteria, proposing that archaea and eukaryotes are evolutionarily derived from within eubacteria.[105] Thomas Cavalier-Smith hypothesizes that the phenotypically diverse phylum Chloroflexi contained the LUCA.[106]

In 2005, Peter Ward proposed that abiotically synthesized RNA became enclosed within a capsule and then created RNA ribozyme replicates. This then bifurcated between Dominion Ribosa (RNA life), Domain Viorea (Viruses), and Dominion Terroa (Cellular life), which contains the LUCA of earlier phylogenic trees.[107]

In 2016, a set of 355 genes likely present in the Last Universal Common Ancestor (LUCA) of all organisms living on Earth was identified.[108] A total of 6.1 million prokaryotic genes from Bacteria and Archaea were sequenced, identifying 355 protein clusters from amongst 286,514 protein clusters that were probably common to LUCA. The result suggest that the LUCA was anaerobic with a Wood–Ljungdahl pathway, nitrogen- and carbon-fixing, thermophilic. Its cofactors suggest dependence upon an environment rich in hydrogen, carbon dioxide, iron, and transition metals. Its genetic code required nucleoside modifications and methylation. LUCA likely inhabited an anaerobic hydrothermal vent setting in a geochemically active environment.[109][110]

Conceptual history until the 1960s

The Miller–Urey experiment was a synthesis of small organic molecules in a mixture of simple gases in a thermal gradient created by heating (right) and cooling (left) the mixture at the same time, with electrical discharges.

An ancient view, from Aristotle and ancient Greek philosophy until the 19th century, is of Spontaneous generation.[111] It held that "lower" animals were generated by decaying organic substances, life arising by chance.[112][113] This was questioned from the 17th century, in works like Thomas Browne's Pseudodoxia Epidemica.[114][115] In 1665, Robert Hooke published the first drawings of a microorganism. In 1676, Antonie van Leeuwenhoek drew and described microorganisms, probably protozoa and bacteria.[116] Van Leeuwenhoek disagreed with spontaneous generation, and by the 1680s convinced himself, using experiments ranging from sealed and open meat incubation and the close study of insect reproduction, that the theory was incorrect.[117] In 1668 Francesco Redi showed that no maggots appeared in meat when flies were prevented from laying eggs.[118] By the middle of the 19th century, spontaneous generation was considered disproven.[119][120]

Panspermia is the hypothesis[121] that life exists throughout the universe, distributed by meteoroids, asteroids, comets[122] and planetoids.[123] It does not attempt to explain how life originated, but shifts the origin to another heavenly body. The advantage is that life is not required to have formed on each planet it occurs on, but rather in a single location, and then spread about the galaxy to other star systems via cometary or meteorite impact.[124]

Several plausible primordial soup hypotheses have been proposed for the origin of life, based on the framework laid out by Alexander Oparin (in 1924) and John Haldane (in 1929), that the first molecules constituting the earliest cells slowly self-organised.[125] Haldane suggested that the Earth's prebiotic oceans would have formed a "hot dilute soup" in which organic compounds could have formed.[113][126]

John Bernal showed that such mechanisms could form most of the necessary molecules for life from inorganic precursors.[127] In 1967, he suggested three "stages": the origin of biological monomers; the origin of biological polymers; and the evolution from molecules to cells.[128][129][130]

In 1952, Stanley Miller and Harold Urey performed the Miller–Urey experiment, demonstrating how organic molecules could have spontaneously formed from inorganic precursors under conditions like those posited by the Oparin-Haldane hypothesis. It used a highly reducing mixture of gases—methane, ammonia, and hydrogen, as well as water vapor—to form simple organic monomers such as amino acids.[131][132]

Primordial origin of biological molecules: chemistry

The chemical processes on the pre-biotic early Earth are called chemical evolution. The elements, except for hydrogen and helium, ultimately derive from stellar nucleosynthesis. In 2016, astronomers reported that the very basic chemical ingredients of life—the carbon-hydrogen molecule (CH, or methylidyne radical), the carbon-hydrogen positive ion (CH+) and the carbon ion (C+)—are largely the result of ultraviolet light from stars, rather than other forms of radiation from supernovae and young stars, as thought earlier.[133] Complex molecules, including organic molecules, form naturally both in space and on planets.[134] There are two possible sources of organic molecules on the early Earth:

  1. Terrestrial origins – organic molecule synthesis driven by impact shocks or by other energy sources (such as UV light, redox coupling, or electrical discharges; e.g., Miller's experiments)
  2. Extraterrestrial origins – formation of organic molecules in interstellar dust clouds, which rain down on planets.[135][136] (See pseudo-panspermia)

Observed extraterrestrial organic molecules

An organic compound is any member of a large class of gaseous, liquid, or solid chemicals whose molecules contain carbon. Carbon is the fourth most abundant element in the Universe by mass after hydrogen, helium, and oxygen.[137] Carbon is abundant in the Sun, stars, comets, and in the atmospheres of most planets.[138] Organic compounds are relatively common in space, formed by "factories of complex molecular synthesis" which occur in molecular clouds and circumstellar envelopes, and chemically evolve after reactions are initiated mostly by ionizing radiation.[134][139][140][141] Based on computer model studies, the complex organic molecules necessary for life may have formed on dust grains in the protoplanetary disk surrounding the Sun before the formation of the Earth.[142] According to the computer studies, this same process may also occur around other stars that acquire planets.[142]

Amino acids

In 2009, the amino acid glycine was found in material ejected from comet Wild 2; it had earlier been detected in meteorites.[143] Comets are encrusted with dark material, thought to be a tar-like organic substance formed from simple carbon compounds under ionizing radiation. A rain of material from comets could have brought such complex organic molecules to Earth.[144][145][146][52] It is estimated that during the Late Heavy Bombardment, meteorites may have delivered up to five million tons of organic prebiotic elements to Earth per year.[52]

PAH world hypothesis

Main page: Biology:PAH world hypothesis

Polycyclic aromatic hydrocarbons (PAH) are the most common and abundant of the known polyatomic molecules in the observable universe,[147][148][149][150] and are a likely constituent of the primordial sea.[147][148][149][150] In 2010, PAHs were detected in nebulae.[151] Polycyclic aromatic hydrocarbons are found in the interstellar medium, in comets, and in meteorites.[138]

The Cat's Paw Nebula lies inside the Milky Way Galaxy and is located in the constellation Scorpius.
Green areas show regions where radiation from hot stars collided with large molecules and small dust grains called "polycyclic aromatic hydrocarbons" (PAHs), causing them to fluoresce.
(Spitzer space telescope, 2018)

Other sources of complex molecules could include extraterrestrial stellar or interstellar origin. In 2004, a team detected traces of PAHs in a nebula.[152] In 2010, another team detected PAHs and fullerenes in nebulae.[151] The use of PAHs has been proposed as a precursor to the RNA world in the PAH world hypothesis.[153] The Spitzer Space Telescope has detected a star, HH 46-IR, forming by a process similar to that by which the Sun formed. In the disk of material surrounding the star, there are molecules including cyanide compounds, hydrocarbons, and carbon monoxide. In 2012, it was shown that PAHs, subjected to interstellar medium conditions, can be transformed, through hydrogenation, oxygenation and hydroxylation, to more complex organics—"a step along the path toward amino acids and nucleotides, the raw materials of proteins and DNA, respectively."[154][155] As a result of these transformations, the PAHs lose their spectroscopic signature, which could explain why they are not seen in "interstellar ice grains, particularly the outer regions of cold, dense clouds or the upper molecular layers of protoplanetary disks."[154][155]

More than 20% of the carbon in the universe may be associated with PAHs.[138][156] PAHs seem to have formed shortly after the Big Bang, are widespread throughout the universe,[147][148][149][150] and are associated with new stars and exoplanets.[138]


Observations suggest that the majority of organic compounds introduced on Earth by interstellar dust particles are principal agents in the formation of complex molecules, thanks to their peculiar surface-catalytic activities.[157][158] Studies reported in 2008, based on 12C/13C isotopic ratios of organic compounds found in the Murchison meteorite, suggested that the RNA component uracil and related molecules, including xanthine, were formed extraterrestrially.[159][160] In 2011, a report based on NASA studies of meteorites found on Earth was published suggesting DNA components (adenine, guanine and related organic molecules) were made in outer space.[157][161][162] The cosmic dust permeating the universe contains complex organics ("amorphous organic solids with a mixed aromaticaliphatic structure") that could be created naturally, and rapidly, by stars.[163][164][165] Sun Kwok of The University of Hong Kong suggested that these compounds may have been related to the development of life on Earth said that "If this is the case, life on Earth may have had an easier time getting started as these organics can serve as basic ingredients for life."[163]

The sugar glycolaldehyde

Formation of glycolaldehyde in stardust

Glycolaldehyde, the first example of an interstellar sugar molecule, was detected in the star-forming region near the centre of our galaxy. It was discovered in 2000 by Jes Jørgensen and Jan Hollis.[166] In 2012, Jørgensen's team reported the detection of glycolaldehyde in a distant star system. The molecule was found around the protostellar binary IRAS 16293-2422 400 light years from Earth.[167][168][169] Glycolaldehyde is needed to form RNA, similar in function to DNA. These findings suggest that complex organic molecules may form in stellar systems prior to the formation of planets, arriving on young planets early in their formation.[170][171] Because sugars are associated with both metabolism and the genetic code, two of the most basic aspects of life, it is thought the discovery of extraterrestrial sugar increases the likelihood that life may exist elsewhere in our galaxy.[166]


A problem in most scenarios of abiogenesis is that the thermodynamic equilibrium of amino acid versus peptides is in the direction of separate amino acids. What has been missing is some force that drives polymerization. The resolution of this problem may well be in the properties of polyphosphates.[172][173] Polyphosphates are formed by polymerization of ordinary monophosphate ions PO43-. Several mechanisms of organic molecule synthesis have been investigated. Polyphosphates cause polymerization of amino acids into peptides. They are also logical precursors in the synthesis of such key biochemical compounds as adenosine triphosphate (ATP). A key issue seems to be that calcium reacts with soluble phosphate to form insoluble calcium phosphate (apatite), so some plausible mechanism must be found to keep calcium ions from causing precipitation of phosphate. There has been much work on this topic over the years, but an interesting new idea is that meteorites may have introduced reactive phosphorus species on the early Earth.[174] Based on computer model studies, the complex organic molecules necessary for life may have formed in the protoplanetary disk of dust grains surrounding the Sun and other stars before the formation of the Earth.[142][175]

The accumulation and concentration of organic molecules on a planetary surface is also considered an essential early step for the origin of life.[36] Identifying and understanding the mechanisms that led to the production of prebiotic molecules in various environments is critical for establishing the inventory of ingredients from which life originated on Earth, assuming that the abiotic production of molecules ultimately influenced the selection of molecules from which life emerged.[36]

In 2019, sugar molecules, including ribose, were detected in meteorites, suggesting that chemical processes on asteroids can produce some essential bio-ingredients, supporting the notion of an RNA world prior to a DNA-based origin of life on Earth, and possibly panspermia.[176][171]

Laboratory synthesis

As early as the 1860s, experiments demonstrated that biologically relevant molecules can be produced from interaction of simple carbon sources with abundant inorganic catalysts.

Fox proteinoids

Main page: Biology:Proteinoid

In trying to uncover the intermediate stages of abiogenesis mentioned by Bernal, Sidney Fox in the 1950s and 1960s studied the spontaneous formation of peptide structures under plausibly early Earth conditions. In one of his experiments, he allowed amino acids to dry out as if puddled in a warm, dry spot in prebiotic conditions: In an experiment to set suitable conditions for life to form, Fox collected volcanic material from a cinder cone in Hawaii. He discovered that the temperature was over 100 °C just 4 inches (100 mm) beneath the surface of the cinder cone, and suggested that this might have been the environment in which life was created—molecules could have formed and then been washed through the loose volcanic ash into the sea. He placed lumps of lava over amino acids derived from methane, ammonia and water, sterilized all materials, and baked the lava over the amino acids for a few hours in a glass oven. A brown, sticky substance formed over the surface, and when the lava was drenched in sterilized water, a thick, brown liquid leached out. He found that, as they dried, the amino acids formed long, often cross-linked, thread-like, submicroscopic polypeptides.[177]


Experiments with the formose reaction by Butlerov showed that tetroses, pentoses, and hexoses are produced when formaldehyde is heated under basic conditions with divalent metal ions like calcium. The reaction was scrutinized and subsequently proposed to be autocatalytic by Breslow in 1959.


Similar experiments demonstrate that nucleobases like guanine and adenine could be synthesized from simple carbon and nitrogen sources like hydrogen cyanide (HCN) and ammonia.[178] Formamide produces all four ribonucleotides when warmed with terrestrial minerals. Formamide is ubiquitous in the Universe, produced by the reaction of water and HCN. It can easily become concentrated through the evaporation of water.[90][91] HCN is poisonous only to aerobic organisms (eukaryotes and aerobic bacteria), which did not yet exist. It can play roles in other chemical processes as well, such as the synthesis of the amino acid glycine.[52]

In 2015, NASA scientists formed DNA and RNA components including uracil, cytosine and thymine in the laboratory under outer space conditions, using starting chemicals such as pyrimidine found in meteorites. Pyrimidine may have been formed in red giant stars or in interstellar dust and gas clouds.[179] All four RNA-bases may be synthesized from formamide in high-energy density events like extraterrestrial impacts.[180]

Effects with temperatures around the freezing point of water

Other pathways for synthesizing bases from inorganic materials were also reported.[181] Orgel and colleagues have shown that freezing temperatures are advantageous for the synthesis of purines, due to the concentrating effect for key precursors such as hydrogen cyanide.[182] Research by Miller and colleagues suggested that while adenine and guanine require freezing conditions for synthesis, cytosine and uracil may require boiling temperatures.[183] Research by the Miller group notes the formation of seven different amino acids and 11 types of nucleobases in ice when ammonia and cyanide were left in a freezer from 1972 to 1997.[184][185] Other work demonstrated the formation of s-triazines (alternative nucleobases), pyrimidines (including cytosine and uracil), and adenine from urea solutions subjected to freeze-thaw cycles under a reductive atmosphere (with spark discharges as an energy source).[186] The explanation given for the unusual speed of these reactions at such a low temperature is eutectic freezing. As an ice crystal forms, it stays pure: only molecules of water join the growing crystal, while impurities like salt or cyanide are excluded. These impurities become crowded in microscopic pockets of liquid within the ice, and this crowding causes the molecules to collide more often. Mechanistic exploration using quantum chemical methods provide a more detailed understanding of some of the chemical processes involved in chemical evolution, and a partial answer to the fundamental question of molecular biogenesis.[187]

Use of less-reducing gas in Miller–Urey experiment

At the time of the Miller–Urey experiment, scientific consensus was that the early Earth had a reducing atmosphere with compounds relatively rich in hydrogen and poor in oxygen (e.g., CH4 and NH3 as opposed to CO2 and nitrogen dioxide (NO2)). However, current scientific consensus describes the primitive atmosphere as either weakly reducing or neutral[188][189] (see also Oxygen Catastrophe). Such an atmosphere would diminish both the amount and variety of amino acids that could be produced, although studies that include iron and carbonate minerals (thought present in early oceans) in the experimental conditions have again produced a diverse array of amino acids.[188] Other scientific research has focused on two other potential reducing environments: outer space and deep-sea thermal vents.[190][191][192]

Synthesis based on hydrogen cyanide

A research project completed in 2015 by John Sutherland and others found that a network of reactions beginning with hydrogen cyanide and hydrogen sulfide, in streams of water irradiated by UV light, could produce the chemical components of proteins and lipids, as well as those of RNA,[193][194] while not producing a wide range of other compounds.[195] The researchers used the term "cyanosulfidic" to describe this network of reactions.[194]

Issues during laboratory synthesis

The spontaneous formation of complex polymers from abiotically generated monomers under the conditions posited by the "soup" theory is not at all a straightforward process. Besides the necessary basic organic monomers, compounds that would have prohibited the formation of polymers were also formed in high concentration during the Miller–Urey and Joan Oró experiments.[196] Biology uses essentially 20 amino acids for its coded protein enzymes, representing a very small subset of the structurally possible set. Most models of the origin of life suggest organisms developed from environmentally available organic compounds.[197] The fundamental roles that peptides play in biology makes it likely that peptides were key players in the origin of life.[198]


Main page: Chemistry:Autocatalysis

Autocatalysts are substances that catalyze the production of themselves and therefore are "molecular replicators." The simplest self-replicating chemical systems are autocatalytic, and typically contain three components: a product molecule and two precursor molecules. The product molecule joins the precursor molecules, which in turn produce more product molecules from more precursor molecules. The product molecule catalyzes the reaction by providing a complementary template that binds to the precursors, thus bringing them together. Such systems have been demonstrated both in biological macromolecules and in small organic molecules.[199]

It has been proposed that life initially arose as autocatalytic chemical networks.[200] British ethologist Richard Dawkins wrote about autocatalysis as a potential explanation for the origin of life in his 2004 book The Ancestor's Tale.[201] In his book, Dawkins cites experiments performed by Julius Rebek and his colleagues in which they combined amino adenosine and pentafluorophenyl esters with the autocatalyst amino adenosine triacid ester (AATE). One product was a variant of AATE, which catalyzed the synthesis of themselves. This experiment demonstrated the possibility that autocatalysts could exhibit competition within a population of entities with heredity, which could be interpreted as a rudimentary form of natural selection.[202][203]

Pertinent geological environments

Darwin's little pond

An early concept, that life originated from non-living matter in slow stages, appeared in Herbert Spencer's 1864–1867 book Principles of Biology. In 1879 William Turner Thiselton-Dyer referred to this in a paper "On spontaneous generation and evolution". On 1 February 1871 Charles Darwin wrote about these publications to Joseph Hooker, and set out his own speculation,[204][205][206] suggesting that the original spark of life may have begun in a

warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, &c., present, that a proteine compound was chemically formed ready to undergo still more complex changes.

He went on to explain that

at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.

A study in 2017 proposed a mathematical model that supports Darwin's concept. They suggest that interplanetary dust particles and meteorites had transported organic molecules like nucleotides to these ponds. For these biopolymers to form in the pools, there would have been wet-dry cycles for polymerization. Ben Pearce and his coauthors theorize that RNA polymers might have appeared prior to 4.17 Gya.[207][208]

Volcanic hot springs and hydrothermal vents, shallow or deep

Early micro-fossils may have come from a hot world of gases such as methane, ammonia, carbon dioxide and hydrogen sulphide, toxic to much current life.[209] Analysis of the conventional threefold tree of life places thermophilic and hyperthermophilic bacteria and archaea closest to the root, suggesting that life may have evolved in a hot environment.[210]

Deep sea hydrothermal vents

Deep-sea hydrothermal vent or black smoker

The deep sea or alkaline hydrothermal vent theory posits that life began at submarine hydrothermal vents.[211][212] Martin and Russell have suggested

that life evolved in structured iron monosulphide precipitates in a seepage site hydrothermal mound at a redox, pH, and temperature gradient between sulphide-rich hydrothermal fluid and iron(II)-containing waters of the Hadean ocean floor. The naturally arising, three-dimensional compartmentation observed within fossilized seepage-site metal sulphide precipitates indicates that these inorganic compartments were the precursors of cell walls and membranes found in free-living prokaryotes. The known capability of FeS and NiS to catalyze the synthesis of the acetyl-methylsulphide from carbon monoxide and methylsulphide, constituents of hydrothermal fluid, indicates that pre-biotic syntheses occurred at the inner surfaces of these metal-sulphide-walled compartments,...[213]

These form where hydrogen-rich fluids emerge from below the sea floor, as a result of serpentinization of ultra-mafic olivine with seawater and a pH interface with carbon dioxide-rich ocean water. The vents form a sustained chemical energy source derived from redox reactions, in which electron donors (molecular hydrogen) react with electron acceptors (carbon dioxide); see Iron–sulfur world theory. These are exothermic reactions.[211][lower-alpha 1]

Russell demonstrated that alkaline vents created an abiogenic proton motive force chemiosmotic gradient,[213] in which conditions are ideal for an abiogenic hatchery for life. Their microscopic compartments "provide a natural means of concentrating organic molecules," composed of iron-sulfur minerals such as mackinawite, endowed these mineral cells with the catalytic properties envisaged by Günter Wächtershäuser.[214] This movement of ions across the membrane depends on a combination of two factors:

  1. Diffusion force caused by concentration gradient—all particles including ions tend to diffuse from higher concentration to lower.
  2. Electrostatic force caused by electrical potential gradient—cations like protons H+ tend to diffuse down the electrical potential, anions in the opposite direction.

These two gradients taken together can be expressed as an electrochemical gradient, providing energy for abiogenic synthesis. The proton motive force can be described as the measure of the potential energy stored as a combination of proton and voltage gradients across a membrane (differences in proton concentration and electrical potential).

Szostak suggested that geothermal activity provides greater opportunities for the origination of life in open lakes where there is a buildup of minerals. In 2010, based on spectral analysis of sea and hot mineral water, Ignat Ignatov and Oleg Mosin demonstrated that life may have predominantly originated in hot mineral water. The hot mineral water that contains hydrocarbonate and calcium ions has the most optimal range.[215][216] This case is similar to the origin of life in hydrothermal vents, but with hydrocarbonate and calcium ions in hot water. The research with spectral analyses was performed in Rupite, Bulgaria, with hot mineral water with calcium and hydrocarbonate ions, Anoxybacillus rupiences sp., bacteria, archaea and cyanobacteria [217][218] Mineral water with pH of 9–11 is possible to have the reactions in seawater. According to Melvin Calvin, certain reactions of condensation-dehydration of amino acids and nucleotides in individual blocks of peptides and nucleic acids can take place in the primary hydrosphere with pH 9–11 at a later evolutionary stage.[219] Some of these compounds like hydrocyanic acid (HCN) have been proven in the experiments of Miller. This is the environment in which the stromatolites have been created. David Ward of Montana State University described the formation of stromatolites in hot mineral water at the Yellowstone National Park. Stromatolites survive in hot mineral water and in proximity to areas with volcanic activity.[220] Processes have evolved in the sea near geysers of hot mineral water. In 2011, Tadashi Sugawara from the University of Tokyo created a protocell in hot water.[221]

The surfaces of mineral particles inside hydrothermal vents have catalytic properties similar to those of enzymes and can create simple organic molecules, such as methanol (CH3OH) and formic, acetic and Pyruvic acid out of the dissolved CO2 in the water, if driven by an applied voltage or by reaction with H2 or H2S.[222][223]

The research reported by Martin in 2016 supports the thesis that life arose at hydrothermal vents,[224][225] that spontaneous chemistry in the Earth's crust driven by rock–water interactions at disequilibrium thermodynamically underpinned life's origin[226][227] and that the founding lineages of the archaea and bacteria were H2-dependent autotrophs that used CO2 as their terminal acceptor in energy metabolism.[228] Martin suggests, based upon this evidence that LUCA "may have depended heavily on the geothermal energy of the vent to survive".[229]

Fluctuating hydrothermal pools on volcanic islands or proto-continents

Mulkidjanian and co-authors think that the marine environments did not provide the ionic balance and composition universally found in cells, as well as of ions required by essential proteins and ribozymes found in virtually all living organisms, especially with respect to K+/Na+ ratio, Mn2+, Zn2+ and phosphate concentrations. The only known environments that mimic the needed conditions on Earth are found in terrestrial hydrothermal pools fed by steam vents.[211] Additionally, mineral deposits in these environments under an anoxic atmosphere would have suitable pH (as opposed to current pools in an oxygenated atmosphere), contain precipitates of sulfide minerals that block harmful UV radiation, have wetting/drying cycles that concentrate substrate solutions to concentrations amenable to spontaneous formation of polymers of nucleic acids, polyesters[230] and depsipeptides,[231] both by chemical reactions in the hydrothermal environment, as well as by exposure to UV light during transport from vents to adjacent pools. Their hypothesized pre-biotic environments are similar to the deep-oceanic vent environments most commonly hypothesized, but add additional components that help explain peculiarities found in reconstructions of the Last Universal Common Ancestor (LUCA) of all living organisms.[232][233]

Colín-García et al. (2016) discuss the advantages and disadvantages of hydrothermal vents as primitive environments.[211] They mention the exergonic reactions in such systems could have been a source of free energy that promoted chemical reactions, additional to their high mineralogical diversity which implies the induction of important chemical gradients, thus favoring the interaction between electron donors and acceptors. Colín-García et al. (2016) also summarize a set of experiments proposed to test the role of hydrothermal vents in prebiotic synthesis.[211]

Volcanic ash in the ocean

Geoffrey W. Hoffmann has argued that a complex nucleation event as the origin of life involving both polypeptides and nucleic acid is compatible with the time and space available in the primary oceans of Earth.[234] Hoffmann suggests that volcanic ash may provide the many random shapes needed in the postulated complex nucleation event. This aspect of the theory can be tested experimentally.

Gold's deep-hot biosphere

In the 1970s, Thomas Gold proposed the theory that life first developed not on the surface of the Earth, but several kilometers below the surface. It is claimed that the discovery of microbial life below the surface of another body in our Solar System would lend significant credence to this theory.[235]

Radioactive beach hypothesis

Zachary Adam claims that tidal processes that occurred during a time when the Moon was much closer may have concentrated grains of uranium and other radioactive elements at the high-water mark on primordial beaches, where they may have been responsible for generating life's building blocks.[236] According to computer models,[237] a deposit of such radioactive materials could show the same self-sustaining nuclear reaction as that found in the Oklo uranium ore seam in Gabon. Such radioactive beach sand might have provided sufficient energy to generate organic molecules, such as amino acids and sugars from acetonitrile in water. Radioactive monazite material also has released soluble phosphate into the regions between sand-grains, making it biologically "accessible." Thus amino acids, sugars, and soluble phosphates might have been produced simultaneously, according to Adam. Radioactive actinides, left behind in some concentration by the reaction, might have formed part of organometallic complexes. These complexes could have been important early catalysts to living processes.

John Parnell has suggested that such a process could provide part of the "crucible of life" in the early stages of any early wet rocky planet, so long as the planet is large enough to have generated a system of plate tectonics which brings radioactive minerals to the surface. As the early Earth is thought to have had many smaller plates, it might have provided a suitable environment for such processes.[238]

Thermodynamics, self-organization, and information: Physics

Thermodynamics principles: Energy and entropy

In antiquity it was commonly thought, for instance by Empedocles and Aristotle, that the life of the individuals of some species, and more generally, life itself, could start with high temperature, i.e. implicitly by thermal cycling.[239]

Life requires a loss of entropy, or disorder, when molecules organize themselves into living matter. Thus, the second law of thermodynamics needs to be considered in abiogenesis and in biology.[240] The emergence of life and increased complexity does not contradict this law: First, a living organism creates order in some places (e.g. its living body or dwelling) at the expense of an increase of entropy elsewhere (e.g. heat and waste production). Second, the Second Law of thermodynamics actually predicts an increase in complexity[241] and in correlations between a system and its surrounding, when undergoing interaction[242] - with memory and genetic adaptation being examples of such correlations between a living organism and its environment.

Obtaining free energy

Bernal said on the Miller–Urey experiment that

it is not enough to explain the formation of such molecules, what is necessary, is a physical-chemical explanation of the origins of these molecules that suggests the presence of suitable sources and sinks for free energy.[243]

Multiple sources of energy were available for chemical reactions on the early Earth. For example, heat (such as from geothermal processes) is a standard energy source for chemistry. Other examples include sunlight and electrical discharges (lightning), among others.[52] In fact, lightning is a plausible energy source for the origin of life, given that just in the tropics lightning strikes about 100 million times a year.[244]

Computer simulations also suggest that cavitation in primordial water reservoirs such as breaking sea waves, streams and oceans can potentially lead to the synthesis of biogenic compounds.[245]

Unfavorable reactions can also be driven by highly favorable ones, as in the case of iron-sulfur chemistry. For example, this was probably important for carbon fixation (the conversion of carbon from its inorganic form to an organic one).[lower-alpha 2] Carbon fixation by reaction of CO2 with H2S via iron-sulfur chemistry is favorable, and occurs at neutral pH and 100 °C. Iron-sulfur surfaces, which are abundant near hydrothermal vents, are also capable of producing small amounts of amino acids and other biological metabolites.[52]


Dissipative structuring

This theory postulates that the hallmark of the origin and evolution of life is the microscopic dissipative structuring under UVC light of organic pigments and their proliferation over the entire Earth surface.[246][247][248] Present day life augments the entropy production of Earth in its solar environment by dissipating ultraviolet and visible photons into heat through organic pigments in water. This heat then catalyzes a host of secondary dissipative processes such as the water cycle, ocean and wind currents, hurricanes, etc.[249]

Self-organization by dissipative structures

Ilya Prigogine circa 1977

The 19th-century physicist Ludwig Boltzmann first recognized that the struggle for existence of living organisms was neither over raw material nor energy, but instead had to do with entropy production derived from the conversion of the solar spectrum into heat by these systems.[250] Boltzmann thus realized that living systems, like all irreversible processes, were dependent on the dissipation of a generalized chemical potential for their existence. In his book "What is Life", the 20th-century physicist Erwin Schrödinger[251] emphasized the importance of Boltzmann's deep insight into the irreversible thermodynamic nature of living systems, suggesting that this was the physics and chemistry behind the origin and evolution of life.

However, irreversible processes, and much less living systems, could not be conveniently analyzed under this perspective until Lars Onsager,[252] and later Ilya Prigogine,[253] developed an elegant mathematical formalism for treating the "self-organization" of material under a generalized chemical potential. This formalism became known as Classical Irreversible Thermodynamics and Prigogine was awarded the Nobel Prize in Chemistry in 1977 for his work on Dissipative systems. His analysis showed that if a system were left to evolve under an imposed external potential, material could spontaneously organize (lower its entropy) forming dissipative structures which would increase the dissipation of the externally imposed potential (augment global entropy production). Non-equilibrium thermodynamics has since been applied by Karo Michaelian and others to the analysis of living systems, from the biochemical production of ATP[254] to optimizing bacterial metabolic pathways[255] to complete ecosystems.[256][257][258][259][260][261]

Encapsulation: morphology

Encapsulation without a membrane

Membraneless polyester droplets

Researchers Tony Jia and Kuhan Chandru[262] have proposed that membraneless polyesters droplets could have been significant in the Origins of Life.[263] Given the "messy" nature of prebiotic chemistry,[264][265] the spontaneous generation of these combinatorial droplets may have played a role in early cellularization before the innovation of lipid vesicles. Protein function within and RNA function in the presence of certain polyester droplets was shown to be preserved within the droplets. Additionally, the droplets have scaffolding ability, by allowing lipids to assemble around them that may have prevented leakage of genetic materials.

Proteinoid microspheres

Fox observed in the 1960s that the proteinoids that he had synthesized could form cell-like structures that have been named "proteinoid microspheres".[177]

The amino acids had combined to form proteinoids, and the proteinoids had combined to form small globules that Fox called "microspheres". His proteinoids were not cells, although they formed clumps and chains reminiscent of cyanobacteria, but they contained no functional nucleic acids or any encoded information. Based upon such experiments, Colin Pittendrigh stated in 1967 that "laboratories will be creating a living cell within ten years," a remark that reflected the typical contemporary naivety about the complexity of cell structures.[266]

Lipid world

Main page: Biology:Gard model

The lipid world theory postulates that the first self-replicating object was lipid-like.[267][268] It is known that phospholipids form lipid bilayers in water while under agitation—the same structure as in cell membranes. These molecules were not present on early Earth, but other amphiphilic long-chain molecules also form membranes. Furthermore, these bodies may expand (by insertion of additional lipids), and under excessive expansion may undergo spontaneous splitting which preserves the same size and composition of lipids in the two progenies. The main idea in this theory is that the molecular composition of the lipid bodies is the preliminary way for information storage, and evolution led to the appearance of polymer entities such as RNA or DNA that may store information favourably. Studies on vesicles from potentially prebiotic amphiphiles have so far been limited to systems containing one or two types of amphiphiles. This in contrast to the output of simulated prebiotic chemical reactions, which typically produce very heterogeneous mixtures of compounds.[269] Within the hypothesis of a lipid bilayer membrane composed of a mixture of various distinct amphiphilic compounds there is the opportunity of a huge number of theoretically possible combinations in the arrangements of these amphiphiles in the membrane. Among all these potential combinations, a specific local arrangement of the membrane would have favoured the constitution of a hypercycle,[270][271] actually a positive feedback composed of two mutual catalysts represented by a membrane site and a specific compound trapped in the vesicle. Such site/compound pairs are transmissible to the daughter vesicles leading to the emergence of distinct lineages of vesicles which would have allowed Darwinian natural selection.[272]


Main page: Biology:Protocell
The three main structures phospholipids form spontaneously in solution: the liposome (a closed bilayer), the micelle and the bilayer.

A protocell is a self-organized, self-ordered, spherical collection of lipids proposed as a stepping-stone to the origin of life.[269] A central question in evolution is how simple protocells first arose and differed in reproductive contribution to the following generation driving the evolution of life. A functional protocell has (as of 2014) not yet been achieved in a laboratory setting.[273][274][275]

Self-assembled vesicles are essential components of primitive cells.[269] The second law of thermodynamics requires that the universe move in a direction in which entropy increases, yet life is distinguished by its great degree of organization. Therefore, a boundary is needed to separate life processes from non-living matter.[276] Irene Chen and Szostak suggest that elementary protocells can give rise to cellular behaviours including primitive forms of differential reproduction, competition, and energy storage.[274] Competition for membrane molecules would favour stabilized membranes, suggesting a selective advantage for the evolution of cross-linked fatty acids and even the phospholipids of today.[274] Such micro-encapsulation would allow for metabolism within the membrane, the exchange of small molecules but the prevention of passage of large substances across it.[277] Encapsulation enables increased solubility of the contained cargo within the capsule and storage of energy in an electrochemical gradient.

Lipid vesicles formation in fresh water

Bruce Damer and David Deamer argue that cell membranes cannot be formed in salty seawater, and must therefore have originated in freshwater. Before the continents formed, the only dry land on Earth would be volcanic islands, where rainwater would form ponds where lipids could form the first stages towards cell membranes. These predecessors of true cells are assumed to have behaved more like a superorganism rather than individual structures, where the porous membranes would house molecules which would leak out and enter other protocells. Only when true cells had evolved would they gradually adapt to saltier environments and enter the ocean.[278]

Vesicles consisting of mixtures of RNA-like biochemicals

Another protocell model is the Jeewanu. First synthesized in 1963 from simple minerals and basic organics while exposed to sunlight, it is still reported to have some metabolic capabilities, the presence of semipermeable membrane, amino acids, phospholipids, carbohydrates and RNA-like molecules.[279][280] However, the nature and properties of the Jeewanu remains to be clarified.

Electrostatic interactions induced by short, positively charged, hydrophobic peptides containing 7 amino acids in length or fewer, can attach RNA to a vesicle membrane, the basic cell membrane.[281][282]

Metal-sulfide precipitates

William Martin and Michael Russell have suggested

. . . . that life evolved in structured iron monosulphide precipitates in a seepage site hydrothermal mound at a redox, pH, and temperature gradient between sulphide-rich hydrothermal fluid and iron(II)-containing waters of the Hadean ocean floor. The naturally arising, three-dimensional compartmentation observed within fossilized seepage-site metal sulphide precipitates indicates that these inorganic compartments were the precursors of cell walls and membranes found in free-living prokaryotes. The known capability of FeS and NiS to catalyze the synthesis of the acetyl-methylsulphide from carbon monoxide and methylsulphide, constituents of hydrothermal fluid, indicates that pre-biotic syntheses occurred at the inner surfaces of these metal-sulphide-walled compartments,..."[213]

Origin of metabolism: physiology

Different forms of life with variable origin processes may have appeared quasi-simultaneously in the early Earth.[283] The other forms may be extinct, having left distinctive fossils through their different biochemistry—e.g., hypothetical types of biochemistry. It has been proposed that:

The first organisms were self-replicating iron-rich clays which fixed carbon dioxide into oxalic and other dicarboxylic acids. This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hotspring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving system which allowed the synthesis of nucleotides and phospholipids. If biosynthesis recapitulates biopoiesis, then the synthesis of amino acids preceded the synthesis of the purine and pyrimidine bases. Furthermore, the polymerization of the amino acid thioesters into polypeptides preceded the directed polymerization of amino acid esters by polynucleotides.[284]

Metabolism-like reactions could have occurred naturally in early oceans, before the first organisms evolved.[20][285] Reconstructions in laboratories show that some of these reactions can produce RNA, and some others resemble two essential reaction cascades of metabolism: glycolysis and the pentose phosphate pathway, that provide essential precursors for nucleic acids, amino acids and lipids.[285]

Clay hypothesis

Montmorillonite, an abundant clay, is a catalyst for the polymerization of RNA and for the formation of membranes from lipids.[286] A model for the origin of life using clay was forwarded by Alexander Cairns-Smith in 1985 and explored as a plausible mechanism by several scientists.[287] The clay hypothesis postulates that complex organic molecules arose gradually on pre-existing, non-organic replication surfaces of silicate crystals in solution.

At the Rensselaer Polytechnic Institute, James Ferris' studies have also confirmed that montmorillonite clay minerals catalyze the formation of RNA in aqueous solution, by joining nucleotides to form longer chains.[288]

In 2007, Bart Kahr from the University of Washington and colleagues reported their experiments that tested the idea that crystals can act as a source of transferable information, using crystals of potassium hydrogen phthalate. "Mother" crystals with imperfections were cleaved and used as seeds to grow "daughter" crystals from solution. They then examined the distribution of imperfections in the new crystals and found that the imperfections in the mother crystals were reproduced in the daughters, but the daughter crystals also had many additional imperfections. For gene-like behavior to be observed, the quantity of inheritance of these imperfections should have exceeded that of the mutations in the successive generations, but it did not. Thus Kahr concluded that the crystals "were not faithful enough to store and transfer information from one generation to the next."[289]

Iron–sulfur world

In the 1980s, Günter Wächtershäuser, encouraged and supported by Karl Popper,[290][291][292] postulated his iron–sulfur world, a theory of the evolution of pre-biotic chemical pathways as the starting point in the evolution of life. It systematically traces today's biochemistry to primordial reactions which provide alternative pathways to the synthesis of organic building blocks from simple gaseous compounds.

In contrast to the classical Miller experiments, which depend on external sources of energy (simulated lightning, ultraviolet irradiation), "Wächtershäuser systems" come with a built-in source of energy: sulfides of iron (iron pyrite) and other minerals. The energy released from redox reactions of these metal sulfides is available for the synthesis of organic molecules, and such systems may have evolved into autocatalytic sets constituting self-replicating, metabolically active entities predating the life forms known today.[20][285] Experiments with such sulfides in an aqueous environment at 100 °C produced a relatively small yield of dipeptides (0.4% to 12.4%) and a smaller yield of tripeptides (0.10%) although under the same conditions, dipeptides were quickly broken down.[293]

Several models reject the self-replication of a "naked-gene", postulating instead the emergence of a primitive metabolism providing a safe environment for the later emergence of RNA replication. The centrality of the Krebs cycle (citric acid cycle) to energy production in aerobic organisms, and in drawing in carbon dioxide and hydrogen ions in biosynthesis of complex organic chemicals, suggests that it was one of the first parts of the metabolism to evolve.[214] Concordantly, geochemists Szostak and Adamala demonstrated non enzymatic RNA replication in primitive protocells is only possibly in presence of weak cation chelator like citric acid, providing further evidence for central role of citric acid in primordial metabolism.[294]

Russell has proposed that "the purpose of life is to hydrogenate carbon dioxide" (as part of a "metabolism-first," rather than a "genetics-first," scenario).[295][296] Physicist Jeremy England has proposed that life was inevitable from general thermodynamic considerations:

... when a group of atoms is driven by an external source of energy (like the sun or chemical fuel) and surrounded by a heat bath (like the ocean or atmosphere), it will often gradually restructure itself in order to dissipate increasingly more energy. This could mean that under certain conditions, matter inexorably acquires the key physical attribute associated with life.[297][298]

One of the earliest incarnations of this idea was put forward in 1924 with Oparin's notion of primitive self-replicating vesicles which predated the discovery of the structure of DNA. Variants in the 1980s and 1990s include Wächtershäuser's iron–sulfur world theory and models introduced by Christian de Duve based on the chemistry of thioesters. More abstract and theoretical arguments for the plausibility of the emergence of metabolism without the presence of genes include a mathematical model introduced by Freeman Dyson in the early 1980s and Stuart Kauffman's notion of collectively autocatalytic sets, discussed later that decade. Kauffman's work has been criticized for ignoring the role of energy in driving biochemical reactions in cells.[299]

Orgel summarized his analysis by stating,

There is at present no reason to expect that multistep cycles such as the reductive citric acid cycle will self-organize on the surface of FeS/FeS2 or some other mineral."[300]

It is possible that another type of metabolic pathway was used at the beginning of life. For example, instead of the reductive citric acid cycle, the "open" acetyl-CoA pathway (another one of the five recognized ways of carbon dioxide fixation in nature today) would be compatible with the idea of self-organization on a metal sulfide surface. The key enzyme of this pathway, carbon monoxide dehydrogenase/acetyl-CoA synthase, harbors mixed nickel-iron-sulfur clusters in its reaction centers and catalyzes the formation of acetyl-CoA (similar to acetyl-thiol) in a single step. There are increasing concerns, however, that prebiotic thiolated and thioester compounds are thermodynamically and kinetically unfavorable to accumulate in presumed prebiotic conditions (i.e. hydrothermal vents).[301] It has also been proposed that cysteine and homocysteine may have reacted with nitriles resulting from the Stecker reaction, readily forming catalytic thiol-rich poplypeptides.[302]

Zinc-world hypothesis

The zinc world (Zn-world) hypothesis of Mulkidjanian [303] is an extension of Wächtershäuser's pyrite hypothesis. Wächtershäuser based his theory of the initial chemical processes leading to informational molecules (RNA, peptides) on a regular mesh of electric charges at the surface of pyrite that may have facilitated the primeval polymerization by attracting reactants and arranging them appropriately relative to each other.[304] The Zn-world theory specifies and differentiates further.[303][305] Hydrothermal fluids rich in H2S interacting with cold primordial ocean (or Darwin's "warm little pond") water leads to the precipitation of metal sulfide particles. Oceanic vent systems and other hydrothermal systems have a zonal structure reflected in ancient volcanogenic massive sulfide deposits (VMS) of hydrothermal origin. They reach many kilometers in diameter and date back to the Archean Eon. Most abundant are pyrite (FeS2), chalcopyrite (CuFeS2), and sphalerite (ZnS), with additions of galena (PbS) and alabandite (MnS). ZnS and MnS have a unique ability to store radiation energy, e.g. from UV light. During the relevant time window of the origins of replicating molecules, the primordial atmospheric pressure was high enough (>100 bar, about 100 atmospheres) to precipitate near the Earth's surface, and UV irradiation was 10 to 100 times more intense than now; hence the unique photosynthetic properties mediated by ZnS provided just the right energy conditions to energize the synthesis of informational and metabolic molecules and the selection of photostable nucleobases.

The Zn-world theory has been further filled out with experimental and theoretical evidence for the ionic constitution of the interior of the first proto-cells before archaea, bacteria and proto-eukaryotes evolved. Archibald Macallum noted the resemblance of body fluids such as blood and lymph to seawater;[306] however, the inorganic composition of all cells differ from that of modern seawater, which led Mulkidjanian and colleagues to reconstruct the "hatcheries" of the first cells combining geochemical analysis with phylogenomic scrutiny of the inorganic ion requirements of universal components of modern cells. The authors conclude that ubiquitous, and by inference primordial, proteins and functional systems show affinity to and functional requirement for K+, Zn2+, Mn2+, and [PO4]3−. Geochemical reconstruction shows that the ionic composition conducive to the origin of cells could not have existed in what we today call marine settings but is compatible with emissions of vapor-dominated zones of what we today call inland geothermal systems. Under the oxygen depleted, CO2-dominated primordial atmosphere, the chemistry of water condensates and exhalations near geothermal fields would resemble the internal milieu of modern cells. Therefore, the precellular stages of evolution may have taken place in shallow "Darwin ponds" lined with porous silicate minerals mixed with metal sulfides and enriched in K+, Zn2+, and phosphorus compounds.[307][308]

Other abiogenesis scenarios

A scenario is a set of related concepts pertinent to the origin of life, such as the Iron-Sulfur world. Some other scenarios, possibly overlapping, may equally account for abiogenesis.

Chemical pathways described by computer

In September 2020, chemists described, for the first time, possible chemical pathways from nonliving prebiotic chemicals to complex biochemicals that could give rise to living organisms, based on a new computer program named AllChemy.[309][310]

The hypercycle

In the early 1970s, Manfred Eigen and Peter Schuster examined the transient stages between the molecular chaos and a self-replicating hypercycle in a prebiotic soup.[311] In a hypercycle, the information storing system (possibly RNA) produces an enzyme, which catalyzes the formation of another information system, in sequence until the product of the last aids in the formation of the first information system. Mathematically treated, hypercycles could create quasispecies, which through natural selection entered into a form of Darwinian evolution. A boost to hypercycle theory was the discovery of ribozymes capable of catalyzing their own chemical reactions. The hypercycle theory requires the existence of complex biochemicals, such as nucleotides, which do not form under the conditions proposed by the Miller–Urey experiment.

Protein amyloid

A new origin-of-life theory based on self-replicating beta-sheet structures has been put forward by Maury in 2009.[312][313] The theory suggest that self-replicating and self-assembling catalytic amyloids were the first informational polymers in a primitive pre-RNA world. The main arguments for the amyloid hypothesis is based on the structural stability, autocatalytic and catalytic properties, and evolvability of beta-sheet based informational systems. Such systems are also error correcting[314] and chiroselective.[315]

Fluctuating salinity: dilute and dry-down

Theories of abiogenesis seldom address the caveat raised by Harold Blum:[316] if the key informational elements of life – proto-nucleic acid chains – spontaneously form duplex structures, then there is no way to dissociate them.

Somewhere in this cycle work must be done, which means that free energy must be expended. If the parts assemble themselves on a template spontaneously, work has to be done to take the replica off; or, if the replica comes off the template of its own accord, work must be done to put the parts on in the first place.

The Oparin–Haldane conjecture addresses the formation, but not the dissociation, of nucleic acid polymers and duplexes. However, nucleic acids are unusual because, in the absence of counterions (low salt) to neutralize the high charges on opposing phosphate groups, the nucleic acid duplex dissociates into single chains.[317] Early tides, driven by a close moon, could have generated rapid cycles of dilution (high tide, low salt) and concentration (dry-down at low tide, high salt) that exclusively promoted the replication of nucleic acids[317] through a process dubbed tidal chain reaction (TCR).[318] This theory has been criticized on the grounds that early tides may not have been so rapid,[319] although regression from current values requires an Earth–Moon juxtaposition at around two Ga, for which there is no evidence, and early tides may have been approximately every seven hours.[320] Another critique is that only 2–3% of the Earth's crust may have been exposed above the sea until late in terrestrial evolution.[321]

The TCR (tidal chain reaction) theory has mechanistic advantages over thermal association/dissociation at deep-sea vents because TCR requires that chain assembly (template-driven polymerization) takes place during the dry-down phase, when precursors are most concentrated, whereas thermal cycling needs polymerization to take place during the cold phase, when the rate of chain assembly is lowest and precursors are likely to be more dilute.

First protein that condenses substrates during thermal cycling: thermosynthesis

Convection cells in fluid placed in a gravity field are selforganizing and enable thermal cycling of the suspended contents in the fluid such as protocells containing protoenzymes that work on thermal cycling.

The thermosynthesis hypothesis considers chemiosmosis more basal than fermentation: the ATP synthase enzyme, which sustains chemiosmosis, is proposed as the currently extant enzyme most closely related to the first metabolic process.[322][323] The thermosynthesis hypothesis does not even invoke a pathway: ATP synthase's binding change mechanism resembles a physical adsorption process that yields free energy. The result would be convection which would bring a continual supply of reactants to the protoenzyme.[324] The described first protein may be simple in the sense that it requires only a short sequence of conserved amino acid residues, a sequent sufficient for the appropriate catalytic cleft.[325]

Pre-RNA world: The ribose issue and its bypass

It is possible that a different type of nucleic acid, such as peptide nucleic acid, threose nucleic acid or glycol nucleic acid, was the first to emerge as a self-reproducing molecule, only later replaced by RNA.[326][327] Larralde et al., say that

the generally accepted prebiotic synthesis of ribose, the formose reaction, yields numerous sugars without any selectivity.[328]

and they conclude that their

results suggest that the backbone of the first genetic material could not have contained ribose or other sugars because of their instability.

The ester linkage of ribose and phosphoric acid in RNA is known to be prone to hydrolysis.[329]

Pyrimidine ribonucleosides and their respective nucleotides have been prebiotically synthesized by a sequence of reactions which by-pass the free sugars, and are assembled in a stepwise fashion by using nitrogenous or oxygenous chemistries. Sutherland has demonstrated high yielding routes to cytidine and uridine ribonucleotides built from small 2 and 3 carbon fragments such as glycolaldehyde, glyceraldehyde or glyceraldehyde-3-phosphate, cyanamide and cyanoacetylene. One of the steps in this sequence allows the isolation of enantiopure ribose aminooxazoline if the enantiomeric excess of glyceraldehyde is 60% or greater.[330] This can be viewed as a prebiotic purification step, where the said compound spontaneously crystallized out from a mixture of the other pentose aminooxazolines. Ribose aminooxazoline can then react with cyanoacetylene in a mild and highly efficient manner to give the alpha cytidine ribonucleotide. Photoanomerization with UV light allows for inversion about the 1' anomeric centre to give the correct beta stereochemistry.[331] In 2009 they showed that the same simple building blocks allow access, via phosphate controlled nucleobase elaboration, to 2',3'-cyclic pyrimidine nucleotides directly, which are known to be able to polymerize into RNA. This paper also highlights the possibility for the photo-sanitization of the pyrimidine-2',3'-cyclic phosphates.[332]

Viral origin

Recent evidence for a "virus first" hypothesis, which may support theories of the RNA world, has been suggested.[333][334] One of the difficulties for the study of the origins of viruses is their high rate of mutation; this is particularly the case in RNA retroviruses like HIV.[335] A 2015 study compared protein fold structures across different branches of the tree of life, where researchers can reconstruct the evolutionary histories of the folds and of the organisms whose genomes code for those folds. They argue that protein folds are better markers of ancient events as their three-dimensional structures can be maintained even as the sequences that code for those begin to change.[333] Thus, the viral protein repertoire retain traces of ancient evolutionary history that can be recovered using advanced bioinformatics approaches. Those researchers think that "the prolonged pressure of genome and particle size reduction eventually reduced virocells into modern viruses (identified by the complete loss of cellular makeup), meanwhile other coexisting cellular lineages diversified into modern cells."[336] The data suggest that viruses originated from ancient cells that co-existed with the ancestors of modern cells. These ancient cells likely contained segmented RNA genomes.[333][337]

A computational model (2015) has shown that virus capsids may have originated in the RNA world and that they served as a means of horizontal transfer between replicator communities since these communities could not survive if the number of gene parasites increased, with certain genes being responsible for the formation of these structures and those that favored the survival of self-replicating communities.[338] The displacement of these ancestral genes between cellular organisms could favor the appearance of new viruses during evolution.[339] Viruses retain a replication module inherited from the prebiotic stage since it is absent in cells.[339] So this is evidence that viruses could originate from the RNA world and could also emerge several times in evolution through genetic escape in cells.[339]

RNA-DNA world

In the latter half of 2020, evidence, based on a plausibly prebiotic simple compound named diamidophosphate (DAP), supporting the notion of a RNA-DNA mixture coevolution, has been presented.[340][341][342][343] The mixture of RNA-DNA sequences, called chimeras, have weak affinity and form weaker duplex structures.[344] This property is advantageous in an abiotic scenario and these chimeras have been shown to replicate RNA and DNA – overcoming the "template-product" inhibition problem, where a pure RNA or pure DNA strand is unable to replicate non-enzymatically because it binds too strongly to its partners.[345] This behavior of chimeric RNA-DNA sequences could lead to an abiotic cross-catalytic amplification of RNA and DNA—a key step toward the simultaneous emergence of RNA and DNA.

Key issues

Protein vs. nucleic acid as the precursor to protein synthesis

Possible precursors for the evolution of protein synthesis include a mechanism to synthesize short peptide cofactors or form a mechanism for the duplication of RNA. It is likely that the ancestral ribosome was composed entirely of RNA, although some roles have since been taken over by proteins. Major remaining questions on this topic include identifying the selective force for the evolution of the ribosome and determining how the genetic code arose.[346]

Eugene Koonin said,

Despite considerable experimental and theoretical effort, no compelling scenarios currently exist for the origin of replication and translation, the key processes that together comprise the core of biological systems and the apparent pre-requisite of biological evolution. The RNA World concept might offer the best chance for the resolution of this conundrum but so far cannot adequately account for the emergence of an efficient RNA replicase or the translation system. The MWO ["many worlds in one"] version of the cosmological model of eternal inflation could suggest a way out of this conundrum because, in an infinite multiverse with a finite number of distinct macroscopic histories (each repeated an infinite number of times), emergence of even highly complex systems by chance is not just possible but inevitable.[347]

Emergence of the genetic code

Error in translation catastrophe

Hoffmann has shown that an early error-prone translation machinery can be stable against an error catastrophe of the type that had been envisaged as problematical for the origin of life, and was known as "Orgel's paradox".[348][349][350]


Main page: Biology:Homochirality

Homochirality is the geometric uniformity of materials composed of chiral (non mirror-symmetric) units. Living organisms use molecules that have the same chirality (handedness): with almost no exceptions,[351] amino acids are left-handed while nucleotides and sugars are right-handed. Chiral molecules can be synthesized, but in the absence of a chiral source or a chiral catalyst, they are formed in a 50/50 (racemic) mixture of both forms. Known mechanisms for the production of non-racemic mixtures from racemic starting materials include: asymmetric physical laws, such as the electroweak interaction; asymmetric environments, such as those caused by circularly polarized light, quartz crystals, or the Earth's rotation, statistical fluctuations during racemic synthesis,[352] and spontaneous symmetry breaking.[353][354][355] Once established, chirality would be selected for.[356] A small bias (enantiomeric excess) in the population can be amplified into a large one by asymmetric autocatalysis, such as in the Soai reaction.[357] In asymmetric autocatalysis, the catalyst is a chiral molecule, which means that a chiral molecule is catalyzing its own production. An initial enantiomeric excess, such as can be produced by polarized light, then allows the more abundant enantiomer to outcompete the other.[358] Homochirality may have started in outer space, as on the Murchison meteorite the amino acid L-alanine is more than twice as frequent as its D form, and L-glutamic acid is more than three times as abundant as its D counterpart.[359][360] Compounds found on meteorites suggest that the chirality of life derives from abiogenic synthesis, since amino acids from meteorites show a left-handed bias, whereas sugars show a predominantly right-handed bias, the same as found in living organisms.[361]


J. Craig Venter

Both Eigen and Sol Spiegelman demonstrated that evolution, including replication, variation, and natural selection, can occur in populations of molecules as well as in organisms.[52] Following on from chemical evolution came the initiation of biological evolution, which led to the first cells.[52] No one has yet synthesized a "protocell" using simple components with the necessary properties of life (the so-called "bottom-up-approach"). Without such a proof-of-principle, explanations have tended to focus on chemosynthesis.[362] However, some researchers, notably Steen Rasmussen and Szostak, have argued that a "top-down approach" is more feasible, starting with simple forms of current life. Spiegelman took advantage of natural selection to synthesize the Spiegelman Monster, which had a genome with just 218 nucleotide bases, having deconstructively evolved from a 4500-base bacterial RNA. Eigen built on Spiegelman's work and produced a similar system further degraded to just 48 or 54 nucleotides—the minimum required for the binding of the replication enzyme.[363] Craig Venter and colleagues engineered existing prokaryotic cells with progressively fewer genes, attempting to discern the minimal requirements for life.[364][365][366]

In 2018, researchers at McMaster University developed a Planet Simulator to help study abiogenesis.[367][368][369][370] It consists of a climate chamber to study how the building blocks of life were assembled and how these transitioned into self-replicating RNA.[367]

See also


Explanatory footnotes

  1. The reactions are:
    Reaction 1: Fayalite + water → magnetite + aqueous silica + hydrogen
    3Fe2SiO4 + 2H2O → 2Fe3O4 + 3SiO2 + 2H2
    Reaction 2: Forsterite + aqueous silica → serpentine
    3Mg2SiO4 + SiO2 + 4H2O → 2Mg3Si2O5(OH)4
    Reaction 3: Forsterite + water → serpentine + brucite
    2Mg2SiO4 + 3H2O → Mg3Si2O5(OH)4 + Mg(OH)2
    Reaction 3 describes the hydration of olivine with water only to yield serpentine and Mg(OH)2 (brucite). Serpentine is stable at high pH in the presence of brucite like calcium silicate hydrate, (C-S-H) phases formed along with portlandite (Ca(OH)2) in hardened Portland cement paste after the hydration of belite (Ca2SiO4), the artificial calcium equivalent of forsterite. Analogy of reaction 3 with belite hydration in ordinary Portland cement: Belite + water → C-S-H phase + portlandite
    2 Ca2SiO4 + 4 H2O → 3 CaO · 2 SiO2 · 3 H2O + Ca(OH)2
  2. The reactions are:
    FeS + H2S → FeS2 + 2H+ + 2e
    FeS + H2S + CO2 → FeS2 + HCOOH


  1. 1.0 1.1 1.2 1.3 1.4 Dodd, Matthew S.; Papineau, Dominic; Grenne, Tor; Slack, John F.; Rittner, Martin; Pirajno, Franco; O'Neil, Jonathan; Little, Crispin T.S. (1 March 2017). "Evidence for early life in Earth's oldest hydrothermal vent precipitates". Nature 543 (7643): 60–64. doi:10.1038/nature21377. PMID 28252057. Bibcode2017Natur.543...60D. Retrieved 2 March 2017. 
  2. 2.0 2.1 2.2 Zimmer, Carl (1 March 2017). "Scientists Say Canadian Bacteria Fossils May Be Earth's Oldest". The New York Times. 
  3. Oparin, Aleksandr Ivanovich (1938). The Origin of Life. Phoenix Edition Series (2 ed.). Mineola, New York: Courier Corporation (published 2003). ISBN 978-0486495224. Retrieved 16 June 2018. 
  4. 4.0 4.1 Peretó, Juli (2005). "Controversies on the origin of life". International Microbiology 8 (1): 23–31. PMID 15906258. Retrieved 1 June 2015. 
  5. Compare: Scharf, Caleb (18 December 2015). "A Strategy for Origins of Life Research". Astrobiology 15 (12): 1031–1042. doi:10.1089/ast.2015.1113. PMID 26684503. Bibcode2015AsBio..15.1031S. "What do we mean by the origins of life (OoL)? ... Since the early 20th century the phrase OoL has been used to refer to the events that occurred during the transition from non-living to living systems on Earth, i.e., the origin of terrestrial biology (Oparin, 1924; Haldane, 1929). The term has largely replaced earlier concepts such as abiogenesis (Kamminga, 1980; Fry, 2000).". 
  6. Oparin 1953, p. vi
  7. Warmflash, David; Warmflash, Benjamin (November 2005). "Did Life Come from Another World?". Scientific American 293 (5): 64–71. doi:10.1038/scientificamerican1105-64. PMID 16318028. Bibcode2005SciAm.293e..64W. 
  8. Yarus 2010, p. 47
  9. Witzany, Guenther (2016). "Crucial steps to life: From chemical reactions to code using agents". BioSystems 140: 49–57. doi:10.1016/j.biosystems.2015.12.007. PMID 26723230. 
  10. Howell, Elizabeth (8 December 2014). "How Did Life Become Complex, And Could It Happen Beyond Earth?". Astrobiology Magazine. 
  11. Tirard, Stephane (20 April 2015). Abiogenesis – Definition. 1. doi:10.1007/978-3-642-27833-4_2-4. ISBN 978-3-642-27833-4. "Thomas Huxley (1825–1895) used the term abiogenesis in an important text published in 1870. He strictly made the difference between spontaneous generation, which he did not accept, and the possibility of the evolution of matter from inert to living, without any influence of life. ... Since the end of the nineteenth century, evolutive abiogenesis means increasing complexity and evolution of matter from inert to living state in the abiotic context of evolution of primitive Earth." 
  12. Levinson, Gene (2020). Rethinking evolution: the revolution that's hiding in plain sight. World Scientific. ISBN 978-1786347268. 
  13. Voet & Voet 2004, p. 29
  14. Dyson 1999
  15. Davies, Paul (1998). The Fifth Miracle, Search for the origin and meaning of life. Penguin. 
  16. Ward, Peter; Kirschvink, Joe (2015). A New History of Life: the radical discoveries about the origins and evolution of life on earth. Bloomsbury Press. pp. 39–40. ISBN 978-1608199105. 
  17. 17.0 17.1
  18. 18.0 18.1 18.2 18.3 Robertson, Michael P.; Joyce, Gerald F. (May 2012). "The origins of the RNA world". Cold Spring Harbor Perspectives in Biology 4 (5): a003608. doi:10.1101/cshperspect.a003608. PMID 20739415. 
  19. 19.0 19.1 19.2 19.3 Cech, Thomas R. (July 2012). "The RNA Worlds in Context". Cold Spring Harbor Perspectives in Biology 4 (7): a006742. doi:10.1101/cshperspect.a006742. PMID 21441585. 
  20. 20.0 20.1 20.2 Keller, Markus A.; Turchyn, Alexandra V.; Ralser, Markus (25 March 2014). "Non-enzymatic glycolysis and pentose phosphate pathway-like reactions in a plausible Archean ocean". Molecular Systems Biology 10 (725): 725. doi:10.1002/msb.20145228. PMID 24771084. 
  21. Graham, Robert W. (February 1990). Extraterrestrial Life in the Universe. Lewis Research Center, Cleveland, Ohio. Retrieved 2015-06-02. 
  22. Altermann 2009, p. xvii
  23. "Age of the Earth". United States Geological Survey. 9 July 2007. 
  24. Dalrymple 2001, pp. 205–221
  25. Manhesa, Gérard; Allègre, Claude J.; Dupréa, Bernard; Hamelin, Bruno (May 1980). "Lead isotope study of basic-ultrabasic layered complexes: Speculations about the age of the earth and primitive mantle characteristics". Earth and Planetary Science Letters 47 (3): 370–382. doi:10.1016/0012-821X(80)90024-2. Bibcode1980E&PSL..47..370M. 
  26. 26.0 26.1 Schopf, J. William; Kudryavtsev, Anatoliy B.; Czaja, Andrew D.; Tripathi, Abhishek B. (5 October 2007). "Evidence of Archean life: Stromatolites and microfossils". Precambrian Research 158 (3–4): 141–155. doi:10.1016/j.precamres.2007.04.009. Bibcode2007PreR..158..141S. 
  27. 27.0 27.1 Schopf, J. William (29 June 2006). "Fossil evidence of Archaean life". Philosophical Transactions of the Royal Society B 361 (1470): 869–885. doi:10.1098/rstb.2006.1834. PMID 16754604. 
  28. 28.0 28.1 Raven & Johnson 2002, p. 68
  29. Staff (9 May 2017). "Oldest evidence of life on land found in 3.48-billion-year-old Australian rocks". 
  30. Djokic, Tara; Van Kranendonk, Martin J.; Campbell, Kathleen A.; Walter, Malcolm R.; Ward, Colin R. (9 May 2017). "Earliest signs of life on land preserved in ca. 3.5 Gao hot spring deposits". Nature Communications 8: 15263. doi:10.1038/ncomms15263. PMID 28486437. Bibcode2017NatCo...815263D. 
  31. Schopf, J. William; Kitajima, Kouki; Spicuzza, Michael J.; Kudryavtsev, Anatolly B.; Valley, John W. (2017). "SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions". PNAS 115 (1): 53–58. doi:10.1073/pnas.1718063115. PMID 29255053. Bibcode2018PNAS..115...53S. 
  32. Tyrell, Kelly April (18 December 2017). "Oldest fossils ever found show life on Earth began before 3.5 billion years ago". University of Wisconsin-Madison. 
  33. Ghosh, Pallab (1 March 2017). "Earliest evidence of life on Earth found". BBC News. 
  34. 34.0 34.1 Dunham, Will (1 March 2017). "Canadian bacteria-like fossils called oldest evidence of life". Reuters. 
  35. "Researchers uncover 'direct evidence' of life on Earth 4 billion years ago". Deutsche Welle. 
  36. 36.0 36.1 36.2 36.3 "NASA Astrobiology Strategy". NASA. 2015. 
  37. Trifonov, Edward N. (17 March 2011). "Vocabulary of Definitions of Life Suggests a Definition". Journal of Biomolecular Structure and Dynamics 29 (2): 259–266. doi:10.1080/073911011010524992. PMID 21875147. 
  38. Gould, James L.; Keeton, William T. (1996). Biological Science (6 ed.). New York: W.W. Norton. 
  39. Campbell, Neil A.; Reece, Jane B. (2005). Biology (7 ed.). Sn Feancisco: Benjamin. 
  40. Casti, John L. (1989). Paradigms lost. Images of man in the mirror of science. New York: Morrow. 
  41. Schulze-Makuch, Dirk; Irwin, Louis N. (2018). "Definition of Life". Life in the Universe. Expectations and Constraints (3 ed.). New York: Springer. 
  42. Voytek, Mary a. (6 March 2021). "About Life Detection". NASA. 
  43. Marshall, Michael (14 December 2020). "He may have found the key to the origins of life. So why have so few heard of him? - Hungarian biologist Tibor Gánti is an obscure figure. Now, more than a decade after his death, his ideas about how life began are finally coming to fruition.". National Geographic Society. 
  44. Mullen, Lesle (1 August 2013). "Defining Life: Q&A with Scientist Gerald Joyce". 
  45. Rabie, Passant (6 July 2020). "Astronomers Have Found The Source Of Life In The Universe". Inverse. 
  46. Marigo, Paola (6 July 2020). "Carbon star formation as seen through the non-monotonic initial–final mass relation". Nature Astronomy 152 (11): 1102–1110. doi:10.1038/s41550-020-1132-1. Bibcode2020NatAs...4.1102M. Retrieved 7 July 2020. 
  47. "WMAP- Life in the Universe". 
  48. Formation of Solar Systems: Solar Nebular Theory. University of Massachusetts Amherst, Department of Astronomy. Accessed on 27 September 2019.
  49. Fesenkov 1959, p. 9
  50. Kasting, James F. (12 February 1993). "Earth's Early Atmosphere". Science 259 (5097): 920–926. doi:10.1126/science.11536547. PMID 11536547. Bibcode1993Sci...259..920K. Retrieved 2015-07-28. 
  51. Morse, John (September 1998). "Hadean Ocean Carbonate Geochemistry". Aquatic Geochemistry 4 (3/4): 301–319. doi:10.1023/A:1009632230875. Bibcode1998MinM...62.1027M. 
  52. 52.0 52.1 52.2 52.3 52.4 52.5 52.6 52.7 52.8 52.9 Follmann, Hartmut; Brownson, Carol (November 2009). "Darwin's warm little pond revisited: from molecules to the origin of life". Naturwissenschaften 96 (11): 1265–1292. doi:10.1007/s00114-009-0602-1. PMID 19760276. Bibcode2009NW.....96.1265F. 
  53. Morse, John W.; MacKenzie, Fred T. (1998). "Hadean Ocean Carbonate Geochemistry". Aquatic Geochemistry 4 (3–4): 301–319. doi:10.1023/A:1009632230875. Bibcode1998MinM...62.1027M. 
  54. Wilde, Simon A.; Valley, John W.; Peck, William H.; Graham, Colin M. (11 January 2001). "Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago". Nature 409 (6817): 175–178. doi:10.1038/35051550. PMID 11196637. Bibcode2001Natur.409..175W. Retrieved 2015-06-03. 
  55. Rosing, Minik T.; Bird, Dennis K.; Sleep, Norman H. et al. (22 March 2006). "The rise of continents – An essay on the geologic consequences of photosynthesis". Palaeogeography, Palaeoclimatology, Palaeoecology 232 (2–4): 99–113. doi:10.1016/j.palaeo.2006.01.007. Bibcode2006PPP...232...99R. Retrieved 2015-06-08. 
  56. Gomes, Rodney; Levison, Hal F.; Tsiganis, Kleomenis; Morbidelli, Alessandro (26 May 2005). "Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets". Nature 435 (7041): 466–469. doi:10.1038/nature03676. PMID 15917802. Bibcode2005Natur.435..466G. 
  57. Sleep, Norman H.; Zahnle, Kevin J.; Kasting, James F. et al. (9 November 1989). "Annihilation of ecosystems by large asteroid impacts on early Earth". Nature 342 (6246): 139–142. doi:10.1038/342139a0. PMID 11536616. Bibcode1989Natur.342..139S. 
  58. Chyba, Christopher; Sagan, Carl (9 January 1992). "Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules: an inventory for the origins of life". Nature 355 (6356): 125–132. doi:10.1038/355125a0. PMID 11538392. Bibcode1992Natur.355..125C. 
  59. Furukawa, Yoshihiro; Sekine, Toshimori; Oba, Masahiro et al. (January 2009). "Biomolecule formation by oceanic impacts on early Earth". Nature Geoscience 2 (1): 62–66. doi:10.1038/NGEO383. Bibcode2009NatGe...2...62F. 
  60. Maher, Kevin A.; Stevenson, David J. (18 February 1988). "Impact frustration of the origin of life". Nature 331 (6157): 612–614. doi:10.1038/331612a0. PMID 11536595. Bibcode1988Natur.331..612M. 
  61. Mann, Adam (2018-01-24). "Bashing holes in the tale of Earth's troubled youth" (in en). Nature 553 (7689): 393–395. doi:10.1038/d41586-018-01074-6. Bibcode2018Natur.553..393M. 
  62. Davies 1999, p. 155
  63. Bock & Goode 1996
  64. Mortillaro, Nicole (1 March 2017). "Oldest traces of life on Earth found in Quebec, dating back roughly 3.8 Gya". CBC News. 
  65. Ohtomo, Yoko; Kakegawa, Takeshi; Ishida, Akizumi et al. (January 2014). "Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks". Nature Geoscience 7 (1): 25–28. doi:10.1038/ngeo2025. Bibcode2014NatGe...7...25O. 
  66. Borenstein, Seth (13 November 2013). "Oldest fossil found: Meet your microbial mom". Excite. Associated Press (Yonkers, NY: Mindspark Interactive Network). 
  67. Noffke, Nora; Christian, Daniel; Wacey, David; Hazen, Robert M. (16 November 2013). "Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Gyo Dresser Formation, Pilbara, Western Australia". Astrobiology 13 (12): 1103–1124. doi:10.1089/ast.2013.1030. PMID 24205812. Bibcode2013AsBio..13.1103N. 
  68. Wade, Nicholas (31 August 2016). "World's Oldest Fossils Found in Greenland". The New York Times. 
  69. Davies 1999
  70. Hassenkam, T.; Andersson, M.P.; Dalby, K.N.; Mackenzie, D.M.A.; Rosing, M.T. (2017). "Elements of Eoarchean life trapped in mineral inclusions". Nature 548 (7665): 78–81. doi:10.1038/nature23261. PMID 28738409. Bibcode2017Natur.548...78H. 
  71. Pearlman, Jonathan (13 November 2013). "Oldest signs of life on Earth found". The Daily Telegraph (London). 
  72. O'Donoghue, James (21 August 2011). "Oldest reliable fossils show early life was a beach". New Scientist 211: 13. doi:10.1016/S0262-4079(11)62064-2. 
  73. Wacey, David; Kilburn, Matt R.; Saunders, Martin et al. (October 2011). "Microfossils of sulphur-metabolizing cells in 3.4-billion-year-old rocks of Western Australia". Nature Geoscience 4 (10): 698–702. doi:10.1038/ngeo1238. Bibcode2011NatGe...4..698W. 
  74. Borenstein, Seth (19 October 2015). "Hints of life on what was thought to be desolate early Earth". AP News (Associated Press). 
  75. Bell, Elizabeth A.; Boehnike, Patrick; Harrison, T. Mark et al. (19 October 2015). "Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon". PNAS 112 (47): 14518–14521. doi:10.1073/pnas.1517557112. PMID 26483481. Bibcode2015PNAS..11214518B.  Early edition, published online before print.
  76. Wolpert, Stuart (19 October 2015). "Life on Earth likely started at least 4.1 billion years ago – much earlier than scientists had thought". Ucla (ULCA). 
  77. Baumgartner, Rafael; Van Kranendonk, Martin; Wacey, David; Fiorentini, Marco; Saunders, Martin; Caruso, Caruso; Pages, Anais; Homann, Martin et al. (2019). "Nano−porous pyrite and organic matter in 3.5-billion-year-old stromatolites record primordial life". Geology 47 (11): 1039–1043. doi:10.1130/G46365.1. Bibcode2019Geo....47.1039B. 
  78. Djokic, Tara; Van Kranendonk, Martin; Cambell, Kathleen; Walter, Malcolm (2017). "Earliest signs of life on land preserved in ca. 3.5 Ga hot spring deposits". Nature Communications 3. 
  79. Lehninger, Albert L. (1970). Biochemistry. The Molecular Basis of Cell Structure and Function. New York: Worth. p. 313. 
  80. Muller, Anthonie W. J. (1995). "Were the first organisms heat engines? A new model for biogenesis and the early evolution of biological energy conversion". Progress in Biophysics and Molecular Biology 63 (2): 193–231. doi:10.1016/0079-6107(95)00004-7. PMID 7542789. 
  81. Muller, Anthonie W. J.; Schulze-Makuch, Dirk (2006). "Thermal energy and the origin of life". Origins of Life and Evolution of Biospheres 36 (2): 77–189. doi:10.1007/s11084-005-9003-4. PMID 16642267. Bibcode2006OLEB...36..177M. 
  82. Zimmer, Carl (25 September 2014). "A Tiny Emissary From the Ancient Past". The New York Times (New York). 
  83. Wade, Nicholas (4 May 2015). "Making Sense of the Chemistry That Led to Life on Earth". The New York Times (New York). 
  84. Benner, S.A.; Bell, E.A.; Biondi, E.; Brasser, R.; Carell, T.; Kim, H.-J.; Mojzsis, S.J.; Omran, A. et al. (2020). "When Did Life Likely Emerge on Earth in an RNA-First Process?". ChemSystemsChem 2 (2). doi:10.1002/syst.201900035. 
  85. Yarus, Michael (April 2011). "Getting Past the RNA World: The Initial Darwinian Ancestor". Cold Spring Harbor Perspectives in Biology 3 (4): a003590. doi:10.1101/cshperspect.a003590. PMID 20719875. 
  86. Fox, George.E. (9 June 2010). "Origin and evolution of the ribosome". Cold Spring Harbor Perspectives in Biology 2 (9(a003483)): a003483. doi:10.1101/cshperspect.a003483. PMID 20534711. 
  87. Neveu, Marc; Kim, Hyo-Joong; Benner, Steven A. (22 April 2013). "The 'Strong' RNA World Hypothesis: Fifty Years Old". Astrobiology 13 (4): 391–403. doi:10.1089/ast.2012.0868. PMID 23551238. Bibcode2013AsBio..13..391N. 
  88. Gilbert, Walter (20 February 1986). "Origin of life: The RNA world". Nature 319 (6055): 618. doi:10.1038/319618a0. Bibcode1986Natur.319..618G. 
  89. Orgel, Leslie E. (October 1994). "The origin of life on Earth". Scientific American 271 (4): 76–83. doi:10.1038/scientificamerican1094-76. PMID 7524147. Bibcode1994SciAm.271d..76O. 
  90. 90.0 90.1 Saladino, Raffaele; Crestini, Claudia; Pino, Samanta et al. (March 2012). "Formamide and the origin of life.". Physics of Life Reviews 9 (1): 84–104. doi:10.1016/j.plrev.2011.12.002. PMID 22196896. Bibcode2012PhLRv...9...84S. 
  91. 91.0 91.1 Saladino, Raffaele; Botta, Giorgia; Pino, Samanta et al. (July 2012). "From the one-carbon amide formamide to RNA all the steps are prebiotically possible". Biochimie 94 (7): 1451–1456. doi:10.1016/j.biochi.2012.02.018. PMID 22738728. 
  92. Lincoln, Tracey A.; Joyce, Gerald F. (27 February 2009). "Self-Sustained Replication of an RNA Enzyme". Science 323 (5918): 1229–1232. doi:10.1126/science.1167856. PMID 19131595. Bibcode2009Sci...323.1229L. 
  93. Joyce, Gerald F. (2009). "Evolution in an RNA world". Cold Spring Harbor Perspectives in Biology 74 (Evolution: The Molecular Landscape): 17–23. doi:10.1101/sqb.2009.74.004. PMID 19667013. 
  94. Szostak, Jack W. (5 February 2015). "The Origins of Function in Biological Nucleic Acids, Proteins, and Membranes". Chevy Chase (CDP), MD: Howard Hughes Medical Institute. 
  95. Bernstein, Harris; Byerly, Henry C.; Hopf, Frederick A. et al. (June 1983). "The Darwinian Dynamic". The Quarterly Review of Biology 58 (2): 185–207. doi:10.1086/413216. 
  96. Michod 1999
  97. Palasek, Stan (23 May 2013). "Primordial RNA Replication and Applications in PCR Technology". arXiv:1305.5581v1 [q-bio.BM].
  98. Koonin, Eugene V.; Senkevich, Tatiana G.; Dolja, Valerian V. (19 September 2006). "The ancient Virus World and evolution of cells". Biology Direct 1: 29. doi:10.1186/1745-6150-1-29. PMID 16984643. 
  99. Vlassov, Alexander V.; Kazakov, Sergei A.; Johnston, Brian H. et al. (August 2005). "The RNA World on Ice: A New Scenario for the Emergence of RNA Information". Journal of Molecular Evolution 61 (2): 264–273. doi:10.1007/s00239-004-0362-7. PMID 16044244. Bibcode2005JMolE..61..264V. 
  100. Nussinov, Mark D.; Otroshchenko, Vladimir A.; Santoli, Salvatore (1997). "The emergence of the non-cellular phase of life on the fine-grained clayish particles of the early Earth's regolith". BioSystems 42 (2–3): 111–118. doi:10.1016/S0303-2647(96)01699-1. PMID 9184757. 
  101. Kühnlein, Alexandra; Lanzmich, Simon A.; Brun, Dieter (2 March 2021). "tRNA sequences can assemble into a replicator". eLife 10. doi:10.7554/eLife.63431. PMID 33648631. 
  102. Maximilian, Ludwig (3 April 2021). "Solving the Chicken-and-the-Egg Problem – "A Step Closer to the Reconstruction of the Origin of Life"". SciTechDaily. 
  103. Boone, David R.; Castenholz, Richard W.; Garrity, George M., eds (2001). The Archaea and the Deeply Branching and Phototrophic Bacteria. Bergey's Manual of Systematic Bacteriology. Springer. ISBN 978-0-387-21609-6. 
  104. Woese, C. R.; Fox, G. E. (1977). "Phylogenetic structure of the prokaryotic domain: the primary kingdoms.". PNAS 7 (11): 5088–5090. doi:10.1073/pnas.74.11.5088. PMID 270744. Bibcode1977PNAS...74.5088W. 
  105. Valas, R. E.; Bourne, P. E. (2011). "The origin of a derived superkingdom: how a gram-positive bacterium crossed the desert to become an archaeon". Biology Direct 6: 16. doi:10.1186/1745-6150-6-16. PMID 21356104. 
  106. Cavalier-Smith, Thomas (2006). "Rooting the tree of life by transition analyses". Biology Direct 1: 19. doi:10.1186/1745-6150-1-19. PMID 16834776. 
  107. Ward, Peter Douglas (2005). Life as We Do Not Know it: The NASA Search for (and Synthesis Of) Alien Life. Viking Books. ISBN 978-0670034581. 
  108. Wade, Nicholas (25 July 2016). "Meet Luca, the Ancestor of All Living Things". The New York Times. 
  109. Weiss, M.C.; Sousa, F.L.; Mrnjavac, N.; Neukirchen, S.; Roettger, M.; Nelson-Sathi, S.; Martin, W.F. (2016). "The physiology and habitat of the last universal common ancestor". Nature Microbiology 1 (9): 16116. doi:10.1038/NMICROBIOL.2016.116. PMID 27562259. 
  110. Nature Vol 535, 28 July 2016,"Early Life Liked it Hot", p.468
  111. Sheldon 2005
  112. Lennox 2001, pp. 229–258
  113. 113.0 113.1 Bernal 1967
  114. Balme, D. M. (1962). "Development of Biology in Aristotle and Theophrastus: Theory of Spontaneous Generation". Phronesis 7 (1–2): 91–104. doi:10.1163/156852862X00052. 
  115. Ross 1652
  116. Dobell 1960
  117. Bondeson 1999
  118. Levine, R.; Evers, C.. "The Slow Death of Spontaneous Generation (1668-1859)". 
  119. Oparin 1953, p. 196
  120. Tyndall 1905, IV, XII (1876), XIII (1878)
  121. Horneck, Gerda; Klaus, David M.; Mancinelli, Rocco L. (March 2010). "Space Microbiology". Microbiology and Molecular Biology Reviews 74 (1): 121–156. doi:10.1128/MMBR.00016-09. PMID 20197502. Bibcode2010MMBR...74..121H. 
  122. Wickramasinghe, Chandra (2011). "Bacterial morphologies supporting cometary panspermia: a reappraisal". International Journal of Astrobiology 10 (1): 25–30. doi:10.1017/S1473550410000157. Bibcode2011IJAsB..10...25W. 
  123. Rampelotto, P. H. (2010). "Panspermia: A promising field of research". In: Astrobiology Science Conference. Abs 5224.
  124. Chang, Kenneth (12 September 2016). "Visions of Life on Mars in Earth's Depths". The New York Times. 
  125. Bahadur, Krishna (1973). "Photochemical Formation of Self–sustaining Coacervates". Proceedings of the Indian National Science Academy 39 (4): 455–467. doi:10.1016/S0044-4057(75)80076-1. PMID 1242552. 
  126. Bryson 2004, pp. 300–302
  127. Bernal 1951
  128. Martin, William F. (January 2003). "On the origins of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells". Phil. Trans. R. Soc. Lond. A 358 (1429): 59–83. doi:10.1098/rstb.2002.1183. PMID 12594918. 
  129. Bernal, John Desmond (September 1949). "The Physical Basis of Life". Proceedings of the Physical Society, Section A 62 (9): 537–558. doi:10.1088/0370-1298/62/9/301. Bibcode1949PPSA...62..537B. 
  130. Kauffman 1995
  131. Miller, Stanley L. (15 May 1953). "A Production of Amino Acids Under Possible Primitive Earth Conditions". Science 117 (3046): 528–529. doi:10.1126/science.117.3046.528. PMID 13056598. Bibcode1953Sci...117..528M. 
  132. Parker, Eric T.; Cleaves, Henderson J.; Dworkin, Jason P. et al. (5 April 2011). "Primordial synthesis of amines and amino acids in a 1958 Miller H2S-rich spark discharge experiment". PNAS 108 (14): 5526–5531. doi:10.1073/pnas.1019191108. PMID 21422282. Bibcode2011PNAS..108.5526P. 
  133. Landau, Elizabeth (12 October 2016). "Building Blocks of Life's Building Blocks Come From Starlight". NASA. 
  134. 134.0 134.1 Ehrenfreund, Pascale; Cami, Jan (December 2010). "Cosmic carbon chemistry: from the interstellar medium to the early Earth.". Cold Spring Harbor Perspectives in Biology 2 (12): a002097. doi:10.1101/cshperspect.a002097. PMID 20554702. 
  135. Gawlowicz, Susan (6 November 2011). "Carbon-based organic 'carriers' in interstellar dust clouds? Newly discovered diffuse interstellar bands". Science Daily (Rockville, MD: ScienceDaily, LLC).  Post is reprinted from materials provided by the Rochester Institute of Technology.
  136. Klyce 2001
  137. "biological abundance of elements". Encyclopedia of Science. Dundee, Scotland: David Darling Enterprises. Retrieved 2008-10-09. 
  138. 138.0 138.1 138.2 138.3 Hoover, Rachel (21 February 2014). "Need to Track Organic Nano-Particles Across the Universe? NASA's Got an App for That". Mountain View, CA: NASA. 
  139. Chang, Kenneth (18 August 2009). "From a Distant Comet, a Clue to Life". The New York Times (New York): p. A18. 
  140. Goncharuk, Vladislav V.; Zui, O. V. (February 2015). "Water and carbon dioxide as the main precursors of organic matter on Earth and in space". Journal of Water Chemistry and Technology 37 (1): 2–3. doi:10.3103/S1063455X15010026. 
  141. Abou Mrad, Ninette; Vinogradoff, Vassilissa; Duvernay, Fabrice et al. (2015). "Laboratory experimental simulations: Chemical evolution of the organic matter from interstellar and cometary ice analogs". Bulletin de la Société Royale des Sciences de Liège 84: 21–32. Bibcode2015BSRSL..84...21A. Retrieved 2015-04-06. 
  142. 142.0 142.1 142.2 Moskowitz, Clara (29 March 2012). "Life's Building Blocks May Have Formed in Dust Around Young Sun". Salt Lake City, UT: Purch. 
  143. "'Life chemical' detected in comet". BBC News (London). 18 August 2009. 
  144. Thompson, William Reid; Murray, B. G.; Khare, Bishun Narain; Sagan, Carl (30 December 1987). "Coloration and darkening of methane clathrate and other ices by charged particle irradiation: Applications to the outer solar system". Journal of Geophysical Research 92 (A13): 14933–14947. doi:10.1029/JA092iA13p14933. PMID 11542127. Bibcode1987JGR....9214933T. 
  145. Stark, Anne M. (5 June 2013). "Life on Earth shockingly comes from out of this world". Livermore, CA: Lawrence Livermore National Laboratory. 
  146. Goldman, Nir; Tamblyn, Isaac (20 June 2013). "Prebiotic Chemistry within a Simple Impacting Icy Mixture". Journal of Physical Chemistry A 117 (24): 5124–5131. doi:10.1021/jp402976n. PMID 23639050. Bibcode2013JPCA..117.5124G. 
  147. 147.0 147.1 147.2 Carey, Bjorn (18 October 2005). "Life's Building Blocks 'Abundant in Space'". Watsonville, California: Imaginova. 
  148. 148.0 148.1 148.2 Hudgins, Douglas M.; Bauschlicher, Charles W. Jr.; Allamandola, Louis J. (10 October 2005). "Variations in the Peak Position of the 6.2 μm Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population". The Astrophysical Journal 632 (1): 316–332. doi:10.1086/432495. Bibcode2005ApJ...632..316H. 
  149. 149.0 149.1 149.2 Des Marais, David J.; Allamandola, Louis J.; Sandford, Scott; Mattioda, Andrew; Gudipati, Murthy; Roser, Joseph; Bramall, Nathan; Nuevo, Michel et al. (2009). "Cosmic Distribution of Chemical Complexity". Mountain View, California: NASA. 
  150. 150.0 150.1 150.2 NASA Ames Research Center (August 2009). "2009 Annual Report to the NASA Astrobiology Institute". 
  151. 151.0 151.1 García-Hernández, Domingo. A.; Manchado, Arturo; García-Lario, Pedro et al. (20 November 2010). "Formation of Fullerenes in H-Containing Planetary Nebulae". The Astrophysical Journal Letters 724 (1): L39–L43. doi:10.1088/2041-8205/724/1/L39. Bibcode2010ApJ...724L..39G. 
  152. Witt, Adolf N.; Vijh, Uma P.; Gordon, Karl D. (January 2004). "Discovery of Blue Fluorescence by Polycyclic Aromatic Hydrocarbon Molecules in the Red Rectangle". American Astronomical Society Meeting 203. Atlanta, Georgia: American Astronomical Society. Bibcode2003AAS...20311017W. Retrieved 16 January 2019. 
  153. d'Ischia, Marco; Manini, Paola; Moracci, Marco; Saladino, Raffaele; Ball, Vincent; Thissen, Helmut; Evans, Richard A.; Puzzarini, Cristina et al. (2019-08-21). "Astrochemistry and Astrobiology: Materials Science in Wonderland?". International Journal of Molecular Sciences 20 (17): 4079. doi:10.3390/ijms20174079. ISSN 1422-0067. PMID 31438518. 
  154. 154.0 154.1 "NASA Cooks Up Icy Organics to Mimic Life's Origins". Ogden, UT: Purch. 20 September 2012. 
  155. 155.0 155.1 Gudipati, Murthy S.; Rui Yang (1 September 2012). "In-situ Probing of Radiation-induced Processing of Organics in Astrophysical Ice Analogs – Novel Laser Desorption Laser Ionization Time-of-flight Mass Spectroscopic Studies". The Astrophysical Journal Letters 756 (1): L24. doi:10.1088/2041-8205/756/1/L24. Bibcode2012ApJ...756L..24G. 
  156. "NASA Ames PAH IR Spectroscopic Database". NASA. 
  157. 157.0 157.1 Gallori, Enzo (June 2011). "Astrochemistry and the origin of genetic material". Rendiconti Lincei 22 (2): 113–118. doi:10.1007/s12210-011-0118-4.  "Paper presented at the Symposium 'Astrochemistry: molecules in space and time' (Rome, 4–5 November 2010), sponsored by Fondazione 'Guido Donegani', Accademia Nazionale dei Lincei."
  158. Martins, Zita (February 2011). "Organic Chemistry of Carbonaceous Meteorites". Elements 7 (1): 35–40. doi:10.2113/gselements.7.1.35. 
  159. Martins, Zita; Botta, Oliver; Fogel, Marilyn L. et al. (15 June 2008). "Extraterrestrial nucleobases in the Murchison meteorite". Earth and Planetary Science Letters 270 (1–2): 130–136. doi:10.1016/j.epsl.2008.03.026. Bibcode2008E&PSL.270..130M. 
  160. "We may all be space aliens: study". Agence France-Presse. Sydney: Australian Broadcasting Corporation. 14 June 2008. 
  161. Callahan, Michael P.; Smith, Karen E.; Cleaves, H. James, II et al. (23 August 2011). "Carbonaceous meteorites contain a wide range of extraterrestrial nucleobases". PNAS 108 (34): 13995–13998. doi:10.1073/pnas.1106493108. PMID 21836052. Bibcode2011PNAS..10813995C. 
  162. Steigerwald, John (8 August 2011). "NASA Researchers: DNA Building Blocks Can Be Made in Space". Goddard Space Flight Center. Greenbelt, MD: NASA. 
  163. 163.0 163.1 Chow, Denise (26 October 2011). "Discovery: Cosmic Dust Contains Organic Matter from Stars". Ogden, UT: Purch. 
  164. The University of Hong Kong (27 October 2011). "Astronomers discover complex organic matter exists throughout the universe". Rockville, MD: ScienceDaily, LLC. 
  165. Sun Kwok; Yong Zhang (3 November 2011). "Mixed aromatic–aliphatic organic nanoparticles as carriers of unidentified infrared emission features". Nature 479 (7371): 80–83. doi:10.1038/nature10542. PMID 22031328. Bibcode2011Natur.479...80K. 
  166. 166.0 166.1 Clemence, Lara; Cohen, Jarrett (7 February 2005). "Space Sugar's a Sweet Find". Goddard Space Flight Center. Greenbelt, MD: NASA. 
  167. Than, Ker (30 August 2012). "Sugar Found in Space: A Sign of Life?". National Geographic News (Washington, D.C.: National Geographic Society). 
  168. "Sweet! Astronomers spot sugar molecule near star". Excite. Associated Press (Yonkers, NY: Mindspark Interactive Network). 29 August 2012. 
  169. "Building blocks of life found around young star". Leiden, the Netherlands: Leiden University. 30 September 2012. 
  170. Jørgensen, Jes K.; Favre, Cécile; Bisschop, Suzanne E. et al. (2012). "Detection of the simplest sugar, glycolaldehyde, in a solar-type protostar with ALMA". The Astrophysical Journal Letters 757 (1): L4. doi:10.1088/2041-8205/757/1/L4. Bibcode2012ApJ...757L...4J. Retrieved 2015-06-23. 
  171. 171.0 171.1 Furukawa, Yoshihiro; Chikaraishi, Yoshito; Ohkouchi, Naohiko; Ogawa, Nanako O.; Glavin, Daniel P.; Dworkin, Jason P.; Abe, Chiaki; Nakamura, Tomoki (2019-11-13). "Extraterrestrial ribose and other sugars in primitive meteorites". Proceedings of the National Academy of Sciences 116 (49): 24440–24445. doi:10.1073/pnas.1907169116. ISSN 0027-8424. PMID 31740594. Bibcode2019PNAS..11624440F. 
  172. Brown, Michael R. W.; Kornberg, Arthur (16 November 2004). "Inorganic polyphosphate in the origin and survival of species". PNAS 101 (46): 16085–16087. doi:10.1073/pnas.0406909101. PMID 15520374. Bibcode2004PNAS..10116085B. 
  173. Clark, David P. (3 August 1999). "The Origin of Life". Carbondale, IL: College of Science; Southern Illinois University Carbondale. 
  174. Pasek, Matthew A. (22 January 2008). "Rethinking early Earth phosphorus geochemistry". PNAS 105 (3): 853–858. doi:10.1073/pnas.0708205105. PMID 18195373. Bibcode2008PNAS..105..853P. 
  175. Ciesla, F.J.; Sandford, S.A. (29 March 2012). "Organic Synthesis via Irradiation and Warming of Ice Grains in the Solar Nebula". Science 336 (6080): 452–454. doi:10.1126/science.1217291. PMID 22461502. Bibcode2012Sci...336..452C. 
  176. Steigerwald, Bill; Jones, Nancy; Furukawa, Yoshihiro (18 November 2019). "First Detection of Sugars in Meteorites Gives Clues to Origin of Life". NASA. 
  177. 177.0 177.1 Walsh, J. Bruce (1995). "Part 4: Experimental studies of the origins of life". Origins of life. Tucson, AZ: University of Arizona. 
  178. Oró, Joan (16 September 1961). "Mechanism of Synthesis of Adenine from Hydrogen Cyanide under Possible Primitive Earth Conditions". Nature 191 (4794): 1193–1194. doi:10.1038/1911193a0. PMID 13731264. Bibcode1961Natur.191.1193O. 
  179. Marlaire, Ruth, ed (3 March 2015). "NASA Ames Reproduces the Building Blocks of Life in Laboratory". Ames Research Center. Moffett Field, CA: NASA. 
  180. Ferus, Martin; Nesvorný, David; Šponer, Jiří; Kubelík, Petr; Michalčíková, Regina; Shestivská, Violetta; Šponer, Judit E.; Civiš, Svatopluk (2015). "High-energy chemistry of formamide: A unified mechanism of nucleobase formation". PNAS 112 (3): 657–662. doi:10.1073/pnas.1412072111. PMID 25489115. Bibcode2015PNAS..112..657F. 
  181. Basile, Brenda; Lazcano, Antonio; Oró, Joan (1984). "Prebiotic syntheses of purines and pyrimidines". Advances in Space Research 4 (12): 125–131. doi:10.1016/0273-1177(84)90554-4. PMID 11537766. Bibcode1984AdSpR...4..125B. 
  182. Orgel, Leslie E. (August 2004). "Prebiotic Adenine Revisited: Eutectics and Photochemistry". Origins of Life and Evolution of Biospheres 34 (4): 361–369. doi:10.1023/B:ORIG.0000029882.52156.c2. PMID 15279171. Bibcode2004OLEB...34..361O. 
  183. Robertson, Michael P.; Miller, Stanley L. (29 June 1995). "An efficient prebiotic synthesis of cytosine and uracil". Nature 375 (6534): 772–774. doi:10.1038/375772a0. PMID 7596408. Bibcode1995Natur.375..772R. 
  184. Fox, Douglas (February 2008). "Did Life Evolve in Ice?". Discover. Retrieved 2008-07-03. 
  185. Levy, Matthew; Miller, Stanley L.; Brinton, Karen; Bada, Jeffrey L. (June 2000). "Prebiotic Synthesis of Adenine and Amino Acids Under Europa-like Conditions". Icarus 145 (2): 609–613. doi:10.1006/icar.2000.6365. PMID 11543508. Bibcode2000Icar..145..609L. 
  186. Menor-Salván, César; Ruiz-Bermejo, Marta; Guzmán, Marcelo I.; Osuna-Esteban, Susana; Veintemillas-Verdaguer, Sabino (20 April 2009). "Synthesis of Pyrimidines and Triazines in Ice: Implications for the Prebiotic Chemistry of Nucleobases". Chemistry 15 (17): 4411–4418. doi:10.1002/chem.200802656. PMID 19288488. 
  187. Roy, Debjani; Najafian, Katayoun; von Ragué Schleyer, Paul (30 October 2007). "Chemical evolution: The mechanism of the formation of adenine under prebiotic conditions". PNAS 104 (44): 17272–17277. doi:10.1073/pnas.0708434104. PMID 17951429. Bibcode2007PNAS..10417272R. 
  188. 188.0 188.1 Cleaves, H. James; Chalmers, John H.; Lazcano, Antonio et al. (April 2008). "A Reassessment of Prebiotic Organic Synthesis in Neutral Planetary Atmospheres". Origins of Life and Evolution of Biospheres 38 (2): 105–115. doi:10.1007/s11084-007-9120-3. PMID 18204914. Bibcode2008OLEB...38..105C. 
  189. Chyba, Christopher F. (13 May 2005). "Rethinking Earth's Early Atmosphere". Science 308 (5724): 962–963. doi:10.1126/science.1113157. PMID 15890865. 
  190. Barton et al. 2007, pp. 93–95
  191. Bada & Lazcano 2009, pp. 56–57
  192. Bada, Jeffrey L.; Lazcano, Antonio (2 May 2003). "Prebiotic Soup – Revisiting the Miller Experiment". Science 300 (5620): 745–746. doi:10.1126/science.1085145. PMID 12730584. Retrieved 2015-06-13. 
  193. Service, Robert F. (16 March 2015). "Researchers may have solved origin-of-life conundrum". Science (Washington, D.C.: American Association for the Advancement of Science). 
  194. 194.0 194.1 Patel, Bhavesh H.; Percivalle, Claudia; Ritson, Dougal J.; Duffy, Colm D.; Sutherland, John D. (April 2015). "Common origins of RNA, protein and lipid precursors in a cyanosulfidic protometabolism". Nature Chemistry 7 (4): 301–307. doi:10.1038/nchem.2202. PMID 25803468. Bibcode2015NatCh...7..301P. 
  195. Patel et al. 2015, p. 302
  196. Oró, Joan; Kimball, Aubrey P. (February 1962). "Synthesis of purines under possible primitive earth conditions: II. Purine intermediates from hydrogen cyanide". Archives of Biochemistry and Biophysics 96 (2): 293–313. doi:10.1016/0003-9861(62)90412-5. PMID 14482339. 
  197. Cleaves II, Henderson (2010). "The origin of the biologically coded amino acids". Journal of Theoretical Biology 263 (4): 490–498. doi:10.1016/j.jtbi.2009.12.014. PMID 20034500. Bibcode2010JThBi.263..490C. 
  198. Frenkel-Pinter, Moran; Mousumi, Samanta; Ashkenasy, Gonen; Leman, Luke (2020). "Prebiotic Peptides: Molecular Hubs in the Origin of Life". Chemical Reviews 263 (4): 490–498. 
  199. Paul, Natasha; Joyce, Gerald F. (December 2004). "Minimal self-replicating systems". Current Opinion in Chemical Biology 8 (6): 634–639. doi:10.1016/j.cbpa.2004.09.005. PMID 15556408. 
  200. Kauffman 1993, chpt. 7
  201. Dawkins 2004
  202. Tjivikua, T.; Ballester, Pablo; Rebek, Julius Jr. (January 1990). "Self-replicating system". Journal of the American Chemical Society 112 (3): 1249–1250. doi:10.1021/ja00159a057. 
  203. Browne, Malcolm W. (30 October 1990). "Chemists Make Molecule With Hint of Life". The New York Times (New York). 
  204. "Letter no. 7471, Charles Darwin to Joseph Dalton Hooker, 1 February (1871)". 
  205. Priscu, John C.. "Origin and Evolution of Life on a Frozen Earth". Arlington County, VA: National Science Foundation. 
  206. Marshall, Michael (11 November 2020). "Charles Darwin's hunch about early life was probably right - In a few scrawled notes to a friend, biologist Charles Darwin theorised how life began. Not only was it probably correct, his theory was a century ahead of its time.". BBC News. 
  207. Pearce, Ben K. D.; Pudritz, Ralph E.; Semenov, Dmitry A.; Henning, Thomas K. (2017-10-24). "Origin of the RNA world: The fate of nucleobases in warm little ponds" (in en). Proceedings of the National Academy of Sciences 114 (43): 11327–11332. doi:10.1073/pnas.1710339114. ISSN 0027-8424. PMID 28973920. Bibcode2017PNAS..11411327P. 
  208. Chung, Emily (October 2, 2017). "Are meteorites the origin of life? 'Warm ponds' theory gets a boost". 
  209. M.D. Brasier (2012), "Secret Chambers: The Inside Story of Cells and Complex Life" (Oxford Uni Press), p.298
  210. Ward, Peter & Kirschvink, Joe, op cit, p. 42
  211. 211.0 211.1 211.2 211.3 211.4 Colín-García, M.; Heredia, A.; Cordero, G.; Camprubí, A.; Negrón-Mendoza, A.; Ortega-Gutiérrez, F.; Berald, H.; Ramos-Bernal, S. (2016). "Hydrothermal vents and prebiotic chemistry: a review". Boletín de la Sociedad Geológica Mexicana 68 (3): 599–620. doi:10.18268/BSGM2016v68n3a13. 
  212. Schirber, Michael (24 June 2014). "Hydrothermal Vents Could Explain Chemical Precursors to Life". NASA. 
  213. 213.0 213.1 213.2 Martin, William; Russell, Michael J. (29 January 2003). "On the origins of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells". Philosophical Transactions of the Royal Society B 358 (1429): 59–83; discussion 83–85. doi:10.1098/rstb.2002.1183. PMID 12594918. 
  214. 214.0 214.1 Lane 2009
  215. Ignatov, Ignat (2011). "Entropy and Time in Living Organisms". Archiv Euromedica 1&2: 74–75. 
  216. Ignatov, Ignat (2021). "Origin of Life and Living Matter in Hot Mineral Water and Properties of Polar Molecules in the Primary Hydrosphere and Hydrothermal Ponds". Uttar Pradesh Journal of Zoology 42 (6): 37–52. 
  217. Derekova, Anna; Sjoholm, Carsten; Mandeva, Rossica; Kambourova, Margarita (2007). "Anoxybacillus rupiences sp. Nov. a novel thermophylic bacterium isolated from Rupi basin (Bulgaria)". Extremophiles 11 (4): 577–583. doi:10.1007/s00792-007-0071-4. PMID 17505776. 
  218. Strunecký, Otakar; Kopejtka, Karel; Goecke, Franz; Tomasch, Juergen; Lukavský, Jaromir; Neori, Amir; Kahe, Silke; Pieper, Dietmar et al. (2019). "High diversity of thermophilic cyanobacteria in Rupite hot spring identified by microscopy, Cultivation, Single-cell PCR and Amplicon sequencing". Extremophiles 23 (9): 35–48. doi:10.1007/s00792-018-1058-z. PMID 30284641. 
  219. Calvin 1969
  220. Schirber, Michael (1 March 2010). "First Fossil-Makers in Hot Water". Astrobiology Magazine. Retrieved 2015-06-19. 
  221. Kurihara, Kensuke; Tamura, Mieko; Shohda, Koh-ichiroh et al. (October 2011). "Self-Reproduction of supramolecular giant vesicles combined with the amplification of encapsulated DNA". Nature Chemistry 3 (10): 775–781. doi:10.1038/nchem.1127. PMID 21941249. Bibcode2011NatCh...3..775K. 
  222. Usher, Oli (27 April 2015). "Chemistry of seabed's hot vents could explain emergence of life" (Press release). University College London. Archived from the original on 20 June 2015. Retrieved 2015-06-19.
  223. Roldan, Alberto; Hollingsworth, Nathan; Roffey, Anna; Islam, Husn-Ubayda et al. (May 2015). "Bio-inspired CO2 conversion by iron sulfide catalysts under sustainable conditions". Chemical Communications 51 (35): 7501–7504. doi:10.1039/C5CC02078F. PMID 25835242. Retrieved 2015-06-19. 
  224. Baross, J.A.; Hoffman, S.E. (1985). "Submarine hydrothermal vents and associated gradient environments as sites for the origin and evolution of life". Origins LifeEvol. B 15 (4): 327–345. doi:10.1007/bf01808177. Bibcode1985OrLi...15..327B. 
  225. Russell, M.J.; Hall, A.J. (1997). "The emergence of life from iron monosulphide bubbles at a submarine hydrothermal redox and pH front". Journal of the Geological Society 154 (3): 377–402. doi:10.1144/gsjgs.154.3.0377. PMID 11541234. Bibcode1997JGSoc.154..377R. 
  226. Amend, J.P.; LaRowe, D.E.; McCollom, T.M.; Shock, E.L. (2013). "The energetics of organic synthesis inside and outside the cell". Phil. Trans. R. Soc. Lond. B 368 (1622): 20120255. doi:10.1098/rstb.2012.0255. PMID 23754809. 
  227. Shock, E.L.; Boyd, E.S. (2015). "Geomicrobiology and microbial geochemistry:principles of geobiochemistry". Elements 11: 389–394. doi:10.2113/gselements.11.6.395. 
  228. Martin, W.; Russell, M.J. (2007). "On the origin of biochemistry at an alkaline hydrothermal vent". Phil. Trans. R. Soc. Lond. B 362 (1486): 1887–1925. doi:10.1098/rstb.2006.1881. PMID 17255002. 
  229. Nature, Vol 535, 28 July 2016. p.468
  230. Chandru, Kuhan; Guttenberg, Nicholas; Giri, Chaitanya; Hongo, Yayoi; Butch, Christopher; Mamajanov, Irena; Cleaves, H. James (31 May 2018). "Simple prebiotic synthesis of high diversity dynamic combinatorial polyester libraries". Communications Chemistry 1 (1). doi:10.1038/s42004-018-0031-1. 
  231. Forsythe, Jay G; Yu, Sheng-Sheng; Mamajanov, Irena; Grover, Martha A; Krishnamurthy, Ramanarayanan; Fernández, Facundo M; Hud, Nicholas V (17 August 2015). "Ester-Mediated Amide Bond Formation Driven by Wet–Dry Cycles: A Possible Path to Polypeptides on the Prebiotic Earth". Angewandte Chemie International Edition in English 54 (34): 9871–9875. doi:10.1002/anie.201503792. PMID 26201989. 
  232. Mulkidjanian, Armid; Bychkov, Andrew; Dibrova, Daria; Galperin, Michael; Koonin, Eugene (3 April 2012). "Origin of first cells at terrestrial, anoxic geothermal fields". PNAS 109 (14): E821–E830. doi:10.1073/pnas.1117774109. PMID 22331915. Bibcode2012PNAS..109E.821M. 
  233. Damer, Bruce; Deamer, David (2020-04-01). "The Hot Spring Hypothesis for an Origin of Life". Astrobiology 20 (4): 429–452. doi:10.1089/ast.2019.2045. ISSN 1531-1074. PMID 31841362. Bibcode2020AsBio..20..429D. 
  234. Hoffmann, Geoffrey William (24 December 2016). "A network theory of the origin of life". bioRxiv 10.1101/096701.
  235. Gold, Thomas (1992). "The Deep, Hot Biosphere". Proceedings of the National Academy of Sciences 89 (13): 6045–6049. doi:10.1073/pnas.89.13.6045. PMID 1631089. Bibcode1992PNAS...89.6045G. 
  236. Dartnell, Lewis (12 January 2008). "Did life begin on a radioactive beach?". New Scientist (2638): 8. Retrieved 2015-06-26. 
  237. Adam, Zachary (2007). "Actinides and Life's Origins". Astrobiology 7 (6): 852–872. doi:10.1089/ast.2006.0066. PMID 18163867. Bibcode2007AsBio...7..852A. 
  238. Parnell, John (December 2004). "Mineral Radioactivity in Sands as a Mechanism for Fixation of Organic Carbon on the Early Earth". Origins of Life and Evolution of Biospheres 34 (6): 533–547. doi:10.1023/B:ORIG.0000043132.23966.a1. PMID 15570707. Bibcode2004OLEB...34..533P. 
  239. Guthrie, W. K. C. (1957). In the beginning: Some Greek views on the origins of life and the early state of man. Methuen, London. 
  240. Simon, Michael A. (1971). The Matter of Life (1 ed.). New Haven and London: Yale University Press. 
  241. Ladyman, J.; Lambert, J.; Weisner, K.B. What is a Complex System? Eur. J. Philos. Sci. 2013, 3, 33–67.
  242. Esposito, M., Lindenberg, K., & Van den Broeck, C. (2010). Entropy production as correlation between system and reservoir. New Journal of Physics, 12(1), 013013.
  243. Bernal 1967, p. 143
  244. Gora, Evan M.; Burchfield, Jeffrey C.; Muller-Landau, Helene C.; Bitzer, Phillip M.; Yanoviak, Stephen P. (2020). "Pantropical geography of lightning-caused disturbance and its implications for tropical forests". Global Change Biology 26 (9): 5017–5026. doi:10.1111/gcb.15227. ISSN 1365-2486. PMID 32564481. Bibcode2020GCBio..26.5017G. 
  245. Kalson, Natan-Haim; Furman, David; Zeiri, Yehuda (2017). "Cavitation-Induced Synthesis of Biogenic Molecules on Primordial Earth". ACS Central Science 3 (9): 1041–1049. doi:10.1021/acscentsci.7b00325. PMID 28979946. 
  246. Michaelian, K (2011). "Thermodynamic dissipation theory for the origin of life". Earth System Dynamics 2 (1): 37–51. doi:10.5194/esd-2-37-2011. Bibcode2011ESD.....2...37M. 
  247. Michaelian, K.; Simeonov, A. (2015-08-19). "Fundamental molecules of life are pigments which arose and co-evolved as a response to the thermodynamic imperative of dissipating the prevailing solar spectrum". Biogeosciences 12 (16): 4913–4937. doi:10.5194/bg-12-4913-2015. ISSN 1726-4170. Bibcode2015BGeo...12.4913M. 
  248. Michaelian, Karo (2017). "Microscopic dissipative structuring and proliferation at the origin of life". Heliyon 3 (10): e00424. doi:10.1016/j.heliyon.2017.e00424. PMID 29062973. 
  249. Michaelian, K (2012). "HESS Opinions 'Biological catalysis of the hydrological cycle: Life's thermodynamic function'". Hydrology and Earth System Sciences 16 (8): 2629–2645. doi:10.5194/hess-16-2629-2012. Bibcode2012HESS...16.2629M. 
  250. Boltzmann, L. (1886) The Second Law of Thermodynamics, in: Ludwig Boltzmann: Theoretical physics and Selected writings, edited by: McGinness, B., D. Reidel, Dordrecht, The Netherlands, 1974.
  251. Schrödinger, Erwin (1944) What is Life? The Physical Aspect of the Living Cell. Cambridge University Press
  252. Onsager, L. (1931) Reciprocal Relations in Irreversible Processes I and II, Phys. Rev. 37, 405; 38, 2265 (1931)
  253. Prigogine, I. (1967) An Introduction to the Thermodynamics of Irreversible Processes, Wiley, New York
  254. Dewar, R; Juretić, D.; Županović, P. (2006). "The functional design of the rotary enzyme ATP synthase is consistent with maximum entropy production". Chem. Phys. Lett. 430 (1): 177–182. doi:10.1016/j.cplett.2006.08.095. Bibcode2006CPL...430..177D. 
  255. Unrean, P., Srienc, F. (2011) Metabolic networks evolve towards states of maximum entropy production, Metabolic Engineering 13, 666–673.
  256. Zotin, A.I. (1984) "Bioenergetic trends of evolutionary progress of organisms", in: Thermodynamics and regulation of biological processes Lamprecht, I. and Zotin, A.I. (eds.), De Gruyter, Berlin, pp. 451–458.
  257. Schneider, E.D.; Kay, J.J. (1994). "Life as a Manifestation of the Second Law of Thermodynamics". Mathematical and Computer Modelling 19 (6–8): 25–48. doi:10.1016/0895-7177(94)90188-0. 
  258. Michaelian, Karo (2005). "Thermodynamic stability of ecosystems". Journal of Theoretical Biology 237 (3): 323–335. doi:10.1016/j.jtbi.2005.04.019. PMID 15978624. Bibcode2004APS..MAR.P9015M. 
  259. Michaelian, Karo; Santillán, Norberto (June 2019). "UVC photon-induced denaturing of DNA: A possible dissipative route to Archean enzyme-less replication". Heliyon 5 (6): e01902. doi:10.1016/j.heliyon.2019.e01902. PMID 31249892. 
  260. Michaelian, Karo (June 2018). "Homochirality through Photon-Induced Denaturing of RNA/DNA at the Origin of Life". Life 8 (2): 21. doi:10.3390/life8020021. PMID 29882802. 
  261. Morales, Julián Mejía; Michaelian, Karo (September 2020). "Photon Dissipation as the Origin of Information Encoding in RNA and DNA". Entropy 22 (9): 940. doi:10.3390/e22090940. PMID 33286709. Bibcode2020Entrp..22..940M. 
  262. Jia, Tony Z.; Chandru, Kuhan; Hongo, Yayoi; Afrin, Rehana; Usui, Tomohiro; Myojo, Kunihiro; Cleaves, H. James (22 July 2019). "Membraneless polyester microdroplets as primordial compartments at the origins of life". Proceedings of the National Academy of Sciences 116 (32): 15830–15835. doi:10.1073/pnas.1902336116. PMID 31332006. 
  263. Chandru, Kuhan; Mamajanov, Irena; Cleaves, H. James; Jia, Tony Z. (January 2020). "Polyesters as a Model System for Building Primitive Biologies from Non-Biological Prebiotic Chemistry". Life 10 (1): 6. doi:10.3390/life10010006. PMID 31963928. 
  264. Marc, Kaufman (18 July 2019). "NASA Astrobiology". 
  265. Guttenberg, Nicholas; Virgo, Nathaniel; Chandru, Kuhan; Scharf, Caleb; Mamajanov, Irena (13 November 2017). "Bulk measurements of messy chemistries are needed for a theory of the origins of life". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375 (2109): 20160347. doi:10.1098/rsta.2016.0347. PMID 29133446. Bibcode2017RSPTA.37560347G. 
  266. Woodward 1969, p. 287
  267. Lancet, Doron (30 December 2014). "Systems Prebiology-Studies of the origin of Life". Rehovot, Israel: Department of Molecular Genetics; Weizmann Institute of Science. 
  268. Segré, Daniel; Ben-Eli, Dafna; Deamer, David W.; Lancet, Doron (February 2001). "The Lipid World". Origins of Life and Evolution of the Biosphere 31 (1–2): 119–145. doi:10.1023/A:1006746807104. PMID 11296516. Bibcode2001OLEB...31..119S. Retrieved 2008-09-11. 
  269. 269.0 269.1 269.2 Chen, Irene A.; Walde, Peter (July 2010). "From Self-Assembled Vesicles to Protocells". Cold Spring Harbor Perspectives in Biology 2 (7): a002170. doi:10.1101/cshperspect.a002170. PMID 20519344. 
  270. Eigen, Manfred; Schuster, Peter (November 1977). "The Hypercycle. A Principle of Natural Self-Organization. Part A: Emergence of the Hypercycle". Naturwissenschaften 64 (11): 541–65. doi:10.1007/bf00450633. PMID 593400. Bibcode1977NW.....64..541E. Retrieved 2015-06-13. 
  271. Markovitch, Omer; Lancet, Doron (Summer 2012). "Excess Mutual Catalysis Is Required for Effective Evolvability". Artificial Life 18 (3): 243–266. doi:10.1162/artl_a_00064. PMID 22662913. 
  272. Tessera, Marc (2011). "Origin of Evolution versus Origin of Life: A Shift of Paradigm". International Journal of Molecular Sciences 12 (6): 3445–3458. doi:10.3390/ijms12063445. PMID 21747687.  Special Issue: "Origin of Life 2011"
  273. "Exploring Life's Origins: Protocells". Arlington County, VA: National Science Foundation. 
  274. 274.0 274.1 274.2 Chen, Irene A. (8 December 2006). "The Emergence of Cells During the Origin of Life". Science 314 (5805): 1558–1559. doi:10.1126/science.1137541. PMID 17158315. 
  275. Zimmer, Carl (26 June 2004). "What Came Before DNA?". Discover. 
  276. Shapiro, Robert (June 2007). "A Simpler Origin for Life". Scientific American 296 (6): 46–53. doi:10.1038/scientificamerican0607-46. PMID 17663224. Bibcode2007SciAm.296f..46S. Retrieved 2015-06-15. 
  277. Chang 2007
  278. Damer, Bruce; Deamer, David (13 March 2015). "Coupled Phases and Combinatorial Selection in Fluctuating Hydrothermal Pools: A Scenario to Guide Experimental Approaches to the Origin of Cellular Life". Life 5 (1): 872–887. doi:10.3390/life5010872. PMID 25780958. 
  279. Grote, Mathias (September 2011). "Jeewanu, or the 'particles of life'". Journal of Biosciences 36 (4): 563–570. doi:10.1007/s12038-011-9087-0. PMID 21857103. Retrieved 2015-06-15. 
  280. Gupta, V.K.; Rai, R.K. (August 2013). "Histochemical localisation of RNA-like material in photochemically formed self-sustaining, abiogenic supramolecular assemblies 'Jeewanu'". International Research Journal of Science & Engineering 1 (1): 1–4. Retrieved 2015-06-15. 
  281. Welter, Kira (10 August 2015). "Peptide glue may have held first protocell components together". Chemistry World (London: Royal Society of Chemistry). 
  282. Kamat, Neha P.; Tobé, Sylvia; Hill, Ian T.; Szostak, Jack W. (29 July 2015). "Electrostatic Localization of RNA to Protocell Membranes by Cationic Hydrophobic Peptides". Angewandte Chemie International Edition 54 (40): 11735–11739. doi:10.1002/anie.201505742. PMID 26223820. 
  283. Davies, Paul (December 2007). "Are Aliens Among Us?". Scientific American 297 (6): 62–69. doi:10.1038/scientificamerican1207-62. Bibcode2007SciAm.297f..62D. Retrieved 2015-07-16. "...if life does emerge readily under terrestrial conditions, then perhaps it formed many times on our home planet. To pursue this possibility, deserts, lakes and other extreme or isolated environments have been searched for evidence of "alien" life-forms—organisms that would differ fundamentally from known organisms because they arose independently.". 
  284. Hartman, Hyman (1998). "Photosynthesis and the Origin of Life". Origins of Life and Evolution of Biospheres 28 (4–6): 515–521. doi:10.1023/A:1006548904157. PMID 11536891. Bibcode1998OLEB...28..515H. 
  285. 285.0 285.1 285.2 Senthilingam, Meera (25 April 2014). "Metabolism May Have Started in Early Oceans Before the Origin of Life" (Press release). Wellcome Trust. EurekAlert!. Archived from the original on 17 June 2015. Retrieved 2015-06-16.
  286. Perry, Caroline (7 February 2011). "Clay-armored bubbles may have formed first protocells" (Press release). Cambridge, MA: Harvard University. EurekAlert!. Archived from the original on 14 July 2015. Retrieved 2015-06-20.
  287. Dawkins 1996, pp. 148–161
  288. Wenhua Huang; Ferris, James P. (12 July 2006). "One-Step, Regioselective Synthesis of up to 50-mers of RNA Oligomers by Montmorillonite Catalysis". Journal of the American Chemical Society 128 (27): 8914–8919. doi:10.1021/ja061782k. PMID 16819887. 
  289. Moore, Caroline (16 July 2007). "Crystals as genes?". Highlights in Chemical Science. Retrieved 2015-06-21. 
  290. Yue-Ching Ho, Eugene (July–September 1990). "Evolutionary Epistemology and Sir Karl Popper's Latest Intellectual Interest: A First-Hand Report". Intellectus 15: 1–3. OCLC 26878740. Retrieved 2012-08-13. 
  291. Wade, Nicholas (22 April 1997). "Amateur Shakes Up Ideas on Recipe for Life". The New York Times (New York). 
  292. Popper, Karl R. (29 March 1990). "Pyrite and the origin of life". Nature 344 (6265): 387. doi:10.1038/344387a0. Bibcode1990Natur.344..387P. 
  293. Huber, Claudia; Wächtershäuser, Günter (31 July 1998). "Peptides by Activation of Amino Acids with CO on (Ni,Fe)S Surfaces: Implications for the Origin of Life". Science 281 (5377): 670–672. doi:10.1126/science.281.5377.670. PMID 9685253. Bibcode1998Sci...281..670H. 
  294. Adamala, Katarzyna; Szostak, Jack W. (2013-11-29). "Nonenzymatic Template-Directed RNA Synthesis Inside Model Protocells". Science 342 (6162): 1098–1100. doi:10.1126/science.1241888. ISSN 0036-8075. PMID 24288333. Bibcode2013Sci...342.1098A. 
  295. Musser, George (23 September 2011). "How Life Arose on Earth, and How a Singularity Might Bring It Down". Observations. 
  296. Carroll, Sean (10 March 2010). "Free Energy and the Meaning of Life". Cosmic Variance. Discover. 
  297. Wolchover, Natalie (22 January 2014). "A New Physics Theory of Life". Quanta Magazine. Retrieved 2015-06-17. 
  298. England, Jeremy L. (28 September 2013). "Statistical physics of self-replication". Journal of Chemical Physics 139 (12): 121923. doi:10.1063/1.4818538. PMID 24089735. Bibcode2013JChPh.139l1923E. Retrieved 2015-06-18. 
  299. Fox, Ronald F. (December 1993). "Review of Stuart Kauffman, The Origins of Order: Self-Organization and Selection in Evolution". Biophys. J. 65 (6): 2698–2699. doi:10.1016/s0006-3495(93)81321-3. Bibcode1993BpJ....65.2698F. 
  300. Orgel, Leslie E. (7 November 2000). "Self-organizing biochemical cycles". PNAS 97 (23): 12503–12507. doi:10.1073/pnas.220406697. PMID 11058157. Bibcode2000PNAS...9712503O. 
  301. Chandru, Kuhan; Gilbert, Alexis; Butch, Christopher; Aono, Masashi; Cleaves, Henderson James II (21 July 2016). "The Abiotic Chemistry of Thiolated Acetate Derivatives and the Origin of Life". Scientific Reports 6 (29883): 29883. doi:10.1038/srep29883. PMID 27443234. Bibcode2016NatSR...629883C. 
  302. Vallee, Yannick; Shalayel, Ibrahim; Ly, Kieu-Dung; Rao, K. V. Raghavendra; Paëpe, Gael De; Märker, Katharina; Milet, Anne (2017-11-08). "At the very beginning of life on Earth: the thiol-rich peptide (TRP) world hypothesis". International Journal of Developmental Biology 61 (8–9): 471–478. doi:10.1387/ijdb.170028yv. PMID 29139533. 
  303. 303.0 303.1 Mulkidjanian, Armen Y. (24 August 2009). "On the origin of life in the zinc world: 1. Photosynthesizing, porous edifices built of hydrothermally precipitated zinc sulfide as cradles of life on Earth". Biology Direct 4: 26. doi:10.1186/1745-6150-4-26. PMID 19703272. 
  304. Wächtershäuser, Günter (December 1988). "Before Enzymes and Templates: Theory of Surface Metabolism". Microbiological Reviews 52 (4): 452–484. doi:10.1128/MMBR.52.4.452-484.1988. PMID 3070320. 
  305. Mulkidjanian, Armen Y.; Galperin, Michael Y. (24 August 2009). "On the origin of life in the zinc world. 2. Validation of the hypothesis on the photosynthesizing zinc sulfide edifices as cradles of life on Earth". Biology Direct 4: 27. doi:10.1186/1745-6150-4-27. PMID 19703275. 
  306. Macallum, A. B. (1 April 1926). "The Paleochemistry of the body fluids and tissues". Physiological Reviews 6 (2): 316–357. doi:10.1152/physrev.1926.6.2.316. 
  307. Mulkidjanian, Armen Y.; Bychkov, Andrew Yu.; Dibrova, Daria V. et al. (3 April 2012). "Origin of first cells at terrestrial, anoxic geothermal fields". PNAS 109 (14): E821–E830. doi:10.1073/pnas.1117774109. PMID 22331915. Bibcode2012PNAS..109E.821M. 
  308. For a deeper integrative version of this hypothesis, see in particular Lankenau 2011, pp. 225–286, interconnecting the "Two RNA worlds" concept and other detailed aspects; and Davidovich, Chen; Belousoff, Matthew; Bashan, Anat; Yonath, Ada (September 2009). "The evolving ribosome: from non-coded peptide bond formation to sophisticated translation machinery". Research in Microbiology 160 (7): 487–492. doi:10.1016/j.resmic.2009.07.004. PMID 19619641. 
  309. Starr, Michelle (3 October 2020). "A New Chemical 'Tree of The Origins of Life' Reveals Our Possible Molecular Evolution". ScienceAlert. 
  310. Wolos, Agnieszka (25 September 2020). "Synthetic connectivity, emergence, and self-regeneration in the network of prebiotic chemistry". Science 369 (6511): eaaw1955. doi:10.1126/science.aaw1955. PMID 32973002. Retrieved 3 October 2020. 
  311. Eigen & Schuster 1979
  312. Maury, CP (2009). "Self-proagating beta-sheet polypeptide structures as prebiotic informational entities:The amyloid world". Origins of Life and Evolution of Biospheres 39 (2): 141–150. doi:10.1007/s11084-009-9165-6. PMID 19301141. 
  313. Maury, CP (2015). "Origin of Life.Primordial genetics: Information transfer in a pre-RNA world based on self-replicating beta-sheet amyloid conformers". Journal of Theoretical Biology 382: 292–297. doi:10.1016/j.jtbi.2015.07.008. PMID 26196585. Bibcode2015JThBi.382..292M. 
  314. Nanda, J; Rubinov, B; Ivnitski, D; Mukherjee, R; Shtelman, E; Motro, Y; Miller, Y; Wagner, N et al. (2017). "Emergence of native peptide seuqences in prebiotic replication networks". Nature Communications 8 (1): 343. doi:10.1038/s41467-017-00463-1. PMID 28874657. Bibcode2017NatCo...8..434N. 
  315. Rout, SK; Friedmann, MP; Riek, R; Greenwald, J (2018). "A prebiotic templated-directed synthesis based on amyloids". Nature Communications 9 (1): 234–242. doi:10.1038/s41467-017-02742-3. PMID 29339755. 
  316. Blum, H.F. (1957). On the origin of self-replicating systems. In Rhythmic and Synthetic Processes in Growth, ed. Rudnick, D., pp. 155–170. Princeton University Press, Princeton, NJ.
  317. 317.0 317.1 Lathe, Richard (2004). "Fast tidal cycling and the origin of life". Icarus 168 (1): 18–22. doi:10.1016/j.icarus.2003.10.018. Bibcode2004Icar..168...18L. 
  318. Lathe, Richard (2005). "Tidal chain reaction and the origin of replicating biopolymers". International Journal of Astrobiology 4 (1): 19–31. doi:10.1017/S1473550405002314. Bibcode2005IJAsB...4...19L. 
  319. Varga, P.; Rybicki, K.; Denis, C. (2006). "Comment on the paper "Fast tidal cycling and the origin of life" by Richard Lathe". Icarus 180 (1): 274–276. doi:10.1016/j.icarus.2005.04.022. Bibcode2006Icar..180..274V. 
  320. Lathe, R. (2006). "Early tides: Response to Varga et al". Icarus 180 (1): 277–280. doi:10.1016/j.icarus.2005.08.019. Bibcode2006Icar..180..277L. 
  321. Flament, Nicolas; Coltice, Nicolas; Rey, Patrice F. (2008). "A case for late-Archaean continental emergence from thermal evolution models and hypsometry". Earth and Planetary Science Letters 275 (3–4): 326–336. doi:10.1016/j.epsl.2008.08.029. Bibcode2008E&PSL.275..326F. 
  322. Muller, Anthonie W. J. (7 August 1985). "Thermosynthesis by biomembranes: Energy gain from cyclic temperature changes". Journal of Theoretical Biology 115 (3): 429–453. doi:10.1016/S0022-5193(85)80202-2. PMID 3162066. Bibcode1985JThBi.115..429M. 
  323. Muller, Anthonie W. J. (1995). "Were the first organisms heat engines? A new model for biogenesis and the early evolution of biological energy conversion". Progress in Biophysics and Molecular Biology 63 (2): 193–231. doi:10.1016/0079-6107(95)00004-7. PMID 7542789. 
  324. Muller, Anthonie W. J.; Schulze-Makuch, Dirk (1 April 2006). "Sorption heat engines: Simple inanimate negative entropy generators". Physica A: Statistical Mechanics and its Applications 362 (2): 369–381. doi:10.1016/j.physa.2005.12.003. Bibcode2006PhyA..362..369M. 
  325. Orgel 1987, pp. 9–16
  326. Orgel, Leslie E. (17 November 2000). "A Simpler Nucleic Acid". Science 290 (5495): 1306–1307. doi:10.1126/science.290.5495.1306. PMID 11185405. 
  327. Nelson, Kevin E.; Levy, Matthew; Miller, Stanley L. (11 April 2000). "Peptide nucleic acids rather than RNA may have been the first genetic molecule". PNAS 97 (8): 3868–3871. doi:10.1073/pnas.97.8.3868. PMID 10760258. Bibcode2000PNAS...97.3868N. 
  328. Larralde, Rosa; Robertson, Michael P.; Miller, Stanley L. (29 August 1995). "Rates of Decomposition of Ribose and Other Sugars: Implications for Chemical Evolution". PNAS 92 (18): 8158–8160. doi:10.1073/pnas.92.18.8158. PMID 7667262. Bibcode1995PNAS...92.8158L. 
  329. Lindahl, Tomas (22 April 1993). "Instability and decay of the primary structure of DNA". Nature 362 (6422): 709–715. doi:10.1038/362709a0. PMID 8469282. Bibcode1993Natur.362..709L. 
  330. Anastasi, Carole; Crowe, Michael A.; Powner, Matthew W.; Sutherland, John D. (18 September 2006). "Direct Assembly of Nucleoside Precursors from Two- and Three-Carbon Units". Angewandte Chemie International Edition 45 (37): 6176–6179. doi:10.1002/anie.200601267. PMID 16917794. 
  331. Powner, Matthew W.; Sutherland, John D. (13 October 2008). "Potentially Prebiotic Synthesis of Pyrimidine β-D-Ribonucleotides by Photoanomerization/Hydrolysis of α-D-Cytidine-2'-Phosphate". ChemBioChem 9 (15): 2386–2387. doi:10.1002/cbic.200800391. PMID 18798212. 
  332. Powner, Matthew W.; Gerland, Béatrice; Sutherland, John D. (14 May 2009). "Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions". Nature 459 (7244): 239–242. doi:10.1038/nature08013. PMID 19444213. Bibcode2009Natur.459..239P. 
  333. 333.0 333.1 333.2 Yates, Diana (25 September 2015). "Study adds to evidence that viruses are alive" (Press release). Champaign, IL: University of Illinois at Urbana–Champaign. Archived from the original on 19 November 2015. Retrieved 2015-10-20.
  334. Janjic, Aleksandar (2018). "The Need for Including Virus Detection Methods in Future Mars Missions". Astrobiology 18 (12): 1611–1614. doi:10.1089/ast.2018.1851. Bibcode2018AsBio..18.1611J. 
  335. Katzourakis, A. (2013). "Paleovirology: Inferring viral evolution from host genome sequence data". Philosophical Transactions of the Royal Society B: Biological Sciences 368 (1626): 20120493. doi:10.1098/rstb.2012.0493. PMID 23938747. 
  336. Arshan, Nasir; Caetano-Anollés, Gustavo (25 September 2015). "A phylogenomic data-driven exploration of viral origins and evolution". Science Advances 1 (8): e1500527. doi:10.1126/sciadv.1500527. PMID 26601271. Bibcode2015SciA....1E0527N. 
  337. Nasir, Arshan; Naeem, Aisha; Jawad Khan, Muhammad et al. (December 2011). "Annotation of Protein Domains Reveals Remarkable Conservation in the Functional Make up of Proteomes Across Superkingdoms". Genes 2 (4): 869–911. doi:10.3390/genes2040869. PMID 24710297. 
  338. Jalasvuori, M.; Mattila, S.; Hoikkala, V. (2015). "Chasing the Origin of Viruses: Capsid-Forming Genes as a Life-Saving Preadaptation within a Community of Early Replicators". PLOS ONE 10 (5): e0126094. doi:10.1371/journal.pone.0126094. PMID 25955384. Bibcode2015PLoSO..1026094J. 
  339. 339.0 339.1 339.2 Krupovic, M.; Dolja, V.V.; Koonin, E.V. (July 2019). "Origin of viruses: primordial replicators recruiting capsids from hosts". Nature Reviews. Microbiology 17 (7): 449–458. doi:10.1038/s41579-019-0205-6. PMID 31142823. 
  340. Gibard, Clémentine; Bhowmik, Subhendu; Karki, Megha; Kim, Eun-Kyong; Krishnamurthy, Ramanarayanan (February 2018). "Phosphorylation, oligomerization and self-assembly in water under potential prebiotic conditions". Nature Chemistry 10 (2): 212–217. doi:10.1038/nchem.2878. ISSN 1755-4349. PMID 29359747. 
  341. Gibard, Clémentine; Gorrell, Ian B.; Jiménez, Eddy I.; Kee, Terence P.; Pasek, Matthew A.; Krishnamurthy, Ramanarayanan (2019). "Geochemical Sources and Availability of Amidophosphates on the Early Earth". Angewandte Chemie International Edition 58 (24): 8151–8155. doi:10.1002/anie.201903808. ISSN 1521-3773. PMID 30989779. 
  342. Krishnamurthy, Ramanarayanan; Jiménez, Eddy I.; Gibard, Clémentine (15 December 2020). "Prebiotic Phosphorylation and Concomitant Oligomerization of Deoxynucleosides to form DNA". Angewandte Chemie 60 (19): 10775–10783. doi:10.1002/anie.202015910. PMID 33325148. Retrieved 28 December 2020. 
  343. The Scripps Research Institute (28 December 2020). "Discovery boosts theory that life on Earth arose from RNA-DNA mix". 
  344. Gavette, Jesse V.; Stoop, Matthias; Hud, Nicholas V.; Krishnamurthy, Ramanarayanan (2016). "RNA–DNA Chimeras in the Context of an RNA World Transition to an RNA/DNA World". Angewandte Chemie International Edition 55 (42): 13204–13209. doi:10.1002/anie.201607919. ISSN 1521-3773. PMID 27650222. 
  345. Bhowmik, Subhendu; Krishnamurthy, Ramanarayanan (November 2019). "The role of sugar-backbone heterogeneity and chimeras in the simultaneous emergence of RNA and DNA". Nature Chemistry 11 (11): 1009–1018. doi:10.1038/s41557-019-0322-x. ISSN 1755-4349. PMID 31527850. Bibcode2019NatCh..11.1009B. 
  346. Noller, Harry F. (April 2012). "Evolution of protein synthesis from an RNA world.". Cold Spring Harbor Perspectives in Biology 4 (4): a003681. doi:10.1101/cshperspect.a003681. PMID 20610545. 
  347. Koonin, Eugene V. (31 May 2007). "The cosmological model of eternal inflation and the transition from chance to biological evolution in the history of life". Biology Direct 2: 15. doi:10.1186/1745-6150-2-15. PMID 17540027. 
  348. Hoffmann, Geoffrey W. (25 June 1974). "On the origin of the genetic code and the stability of the translation apparatus". Journal of Molecular Biology 86 (2): 349–362. doi:10.1016/0022-2836(74)90024-2. PMID 4414916. 
  349. Orgel, Leslie E. (April 1963). "The Maintenance of the Accuracy of Protein Synthesis and its Relevance to Ageing". PNAS 49 (4): 517–521. doi:10.1073/pnas.49.4.517. PMID 13940312. Bibcode1963PNAS...49..517O. 
  350. Hoffmann, Geoffrey W. (October 1975). "The Stochastic Theory of the Origin of the Genetic Code". Annual Review of Physical Chemistry 26: 123–144. doi:10.1146/annurev.pc.26.100175.001011. Bibcode1975ARPC...26..123H. 
  351. Chaichian, Rojas & Tureanu 2014, pp. 353–364
  352. Plasson, Raphaël; Kondepudi, Dilip K.; Bersini, Hugues et al. (August 2007). "Emergence of homochirality in far-from-equilibrium systems: Mechanisms and role in prebiotic chemistry". Chirality 19 (8): 589–600. doi:10.1002/chir.20440. PMID 17559107.  "Special Issue: Proceedings from the Eighteenth International Symposium on Chirality (ISCD-18), Busan, Korea, 2006"
  353. Jafarpour, Farshid; Biancalani, Tommaso; Goldenfeld, Nigel (2017). "Noise-induced symmetry breaking far from equilibrium and the emergence of biological homochirality". Physical Review E 95 (3): 032407. doi:10.1103/PhysRevE.95.032407. PMID 28415353. Bibcode2017PhRvE..95c2407J. 
  354. Jafarpour, Farshid; Biancalani, Tommaso; Goldenfeld, Nigel (2015). "Noise-induced mechanism for biological homochirality of early life self-replicators". Physical Review Letters 115 (15): 158101. doi:10.1103/PhysRevLett.115.158101. PMID 26550754. Bibcode2015PhRvL.115o8101J. 
  355. Frank, F.C. (1953). "On spontaneous asymmetric synthesis". Biochimica et Biophysica Acta 11 (4): 459–463. doi:10.1016/0006-3002(53)90082-1. PMID 13105666. 
  356. Clark, Stuart (July–August 1999). "Polarized Starlight and the Handedness of Life". American Scientist 87 (4): 336. doi:10.1511/1999.4.336. Bibcode1999AmSci..87..336C. 
  357. Shibata, Takanori; Morioka, Hiroshi; Hayase, Tadakatsu et al. (17 January 1996). "Highly Enantioselective Catalytic Asymmetric Automultiplication of Chiral Pyrimidyl Alcohol". Journal of the American Chemical Society 118 (2): 471–472. doi:10.1021/ja953066g. 
  358. Soai, Kenso; Sato, Itaru; Shibata, Takanori (2001). "Asymmetric autocatalysis and the origin of chiral homogeneity in organic compounds". The Chemical Record 1 (4): 321–332. doi:10.1002/tcr.1017. PMID 11893072. 
  359. Hazen 2005, p. 184
  360. Meierhenrich, Uwe (2008). Amino acids and the asymmetry of life caught in the act of formation. Berlin: Springer. pp. 76–79. ISBN 978-3540768869. 
  361. Mullen, Leslie (5 September 2005). "Building Life from Star-Stuff". Astrobiology Magazine. Retrieved 2015-06-15. 
  362. McCollom, Thomas; Mayhew, Lisa; Scott, Jim (7 October 2014). "NASA awards CU-Boulder-led team $7 million to study origins, evolution of life in universe" (Press release). Boulder, CO: University of Colorado Boulder. Archived from the original on 31 July 2015. Retrieved 2015-06-08.
  363. Oehlenschläger, Frank; Eigen, Manfred (December 1997). "30 Years Later – a New Approach to Sol Spiegelman's and Leslie Orgel's in vitro Evolutionary Studies Dedicated to Leslie Orgel on the occasion of his 70th birthday". Origins of Life and Evolution of Biospheres 27 (5–6): 437–457. doi:10.1023/A:1006501326129. PMID 9394469. Bibcode1997OLEB...27..437O. 
  364. Gibson, Daniel G.; Glass, John I.; Lartigue, Carole et al. (2 July 2010). "Creation of a Bacterial Cell Controlled by a Chemically Synthesized Genome". Science 329 (5987): 52–56. doi:10.1126/science.1190719. PMID 20488990. Bibcode2010Sci...329...52G. 
  365. Swaby, Rachel (20 May 2010). "Scientists Create First Self-Replicating Synthetic Life". Wired (New York). 
  366. Coughlan, Andy (2016) "Smallest ever genome comes to life: Humans built it but we don't know what a third of its genes actually do" (New Scientist 2 April 2016 No 3067)p.6
  367. 367.0 367.1 Balch, Erica (4 October 2018). "Ground-breaking lab poised to unlock the mystery of the origins of life on Earth and beyond". McMaster University. 
  368. Staff (4 October 2018). "Ground-breaking lab poised to unlock the mystery of the origins of life". EurekAlert!. 
  369. Staff (2018). "Planet Simulator". 
  370. Anderson, Paul Scott (14 October 2018). "New technology may help solve mystery of life's origins – How did life on Earth begin? A new technology, called Planet Simulator, might finally help solve the mystery.". EarthSky. 

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