View source for Biology:Paleontology

{{Short description|Study of life before 11,700 years ago}}
{{Redirect|Palaeontology|the
Science journal|Palaeontology (journal)}}
{{Paleontology}}
[[File:Joda paleontologist.jpg|thumb|A paleontologist at work at John Day Fossil Beds National Monument]]

'''Paleontology''' ({{IPAc-en|ˌ|p|eɪ|l|i|ɒ|n|ˈ|t|ɒ|l|ə|dʒ|i|,_|ˌ|p|æ|l|i|-|,_|-|ən|-}}), also spelled '''palaeontology'''{{Efn|Outside the United States}} or '''palæontology''', is the scientific study of life that existed prior to, and sometimes including, the start of the [[Earth:Holocene|Holocene]] [[Earth:Epoch (geology)|epoch]] (roughly 11,700 years before present). It includes the study of [[Biology:Fossil|fossil]]s to classify organisms and study their [[Biology:Biological interaction|interactions]] with each other and their environments (their [[Earth:Paleoecology|paleoecology]]). Paleontological observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of [[Biography:Georges Cuvier|Georges Cuvier]]'s work on comparative anatomy, and developed rapidly in the 19th century. The term has been used since 1822<ref name=cuchet>{{cite book |title=Journal de physique, de chimie, d'histoire naturelle et des arts |date=1822 |publisher=Cuchet |location=Paris |page=[https://gallica.bnf.fr/ark:/12148/bpt6k96079365/f60.image.r=paloeontologie liv] |url=https://gallica.bnf.fr/ark:/12148/bpt6k96079365?rk=42918;4 |language=EN}}</ref>{{efn|In 1822, Henri Marie Ducrotay de Blainville used the French term ''palœontologie''.{{r|cuchet}} In 1838, Charles Lyell used the English term ''palæontology'' in ''Elements of Geology''.<ref>{{cite book |last1=Lyell |first1=Charles |title=Elements of geology |date=1838 |publisher=J. Murray |location=London |page=[https://archive.org/details/elementsgeology06lyelgoog/page/281 281] |url=https://archive.org/details/elementsgeology06lyelgoog}}</ref>}} formed from [[Social:Ancient language|Greek]] {{lang|grc|παλαιός}} ({{transliteration|grc|'palaios'}}, "old, ancient"), {{lang|grc|ὄν}} ({{transliteration|grc|'on'}}, (gen. {{transliteration|grc|'ontos'}}), "being, creature"), and {{lang|grc|λόγος}} ({{transliteration|grc|'logos'}}, "speech, thought, study").<ref name=OnlineEtDict>{{cite dictionary |title=paleontology |url = http://www.etymonline.com/index.php?term=paleontology&allowed_in_frame=0|dictionary=Online Etymology Dictionary|url-status=live|archive-url=https://web.archive.org/web/20130307065643/http://etymonline.com/index.php?term=paleontology&allowed_in_frame=0 |archive-date=March 7, 2013}}</ref>

Paleontology lies on the border between [[Biology:Biology|biology]] and [[Earth:Geology|geology]], but it differs from [[Earth:Archaeology|archaeology]] in that it excludes the study of anatomically modern humans. It now uses techniques drawn from a wide range of sciences, including [[Biology:Biochemistry|biochemistry]], mathematics, and engineering. Use of all these techniques has enabled paleontologists to discover much of the [[Biology:Evolutionary history of life|evolutionary history of life]], almost all the way back to when Earth became capable of supporting life, nearly 4&nbsp;billion years ago.<ref>{{cite journal |last1=Doolittle |first1=W. Ford |last2=Worm |first2=Boris |url=http://shiva.msu.montana.edu/courses/mb437_537_2005_fall/docs/uprooting.pdf |archive-url=https://web.archive.org/web/20110715111244/http://shiva.msu.montana.edu/courses/mb437_537_2005_fall/docs/uprooting.pdf |archive-date=July 15, 2011 |title=Uprooting the tree of life |journal=Scientific American |date=February 2000 |volume=282 |issue=6 |pages=90–95 |doi=10.1038/scientificamerican0200-90 |pmid=10710791 |url-status=dead |bibcode=2000SciAm.282b..90D}}</ref> As knowledge has increased, paleontology has developed specialised sub-divisions, some of which focus on different types of fossil organisms while others study [[Earth:Paleoecology|ecology]] and environmental history, such as [[Earth:Paleoclimatology|ancient climates]].

Body fossils and [[Biology:Trace fossil|trace fossil]]s are the principal types of evidence about ancient life, and [[Chemistry:Geochemistry|geochemical]] evidence has helped to decipher the evolution of life before there were organisms large enough to leave body fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow [[Physics:Radiometric dating|radiometric dating]], which provides [[Physics:Absolute dating|absolute dates]] that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving the "jigsaw puzzles" of [[Earth:Biostratigraphy|biostratigraphy]] (arrangement of rock layers from youngest to oldest). Classifying ancient organisms is also difficult, as many do not fit well into the [[Linnaean taxonomy]] classifying living organisms, and paleontologists more often use [[Biology:Cladistics|cladistics]] to draw up evolutionary "family trees". The final quarter of the 20th century saw the development of [[Biology:Molecular phylogenetics|molecular phylogenetics]], which investigates how closely organisms are related by measuring the similarity of the [[Biology:DNA|DNA]] in their [[Biology:Genome|genome]]s. Molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the [[Biology:Molecular clock|molecular clock]] on which such estimates depend.

== Overview ==
The simplest definition of "paleontology" is "the study of ancient life".<ref name="CowenHistLifeEd3Pxi">{{Cite book
| author=Cowen, R. | title=History of Life | date=2000 | pages=xi, 47–50, 61
| publisher=Blackwell Science | edition=3rd | isbn=0-632-04444-6
}}</ref> The field seeks information about several aspects of past organisms: "their identity and origin, their environment and evolution, and what they can tell us about the Earth's organic and inorganic past".<ref>{{Cite journal
| author= Laporte, L.F. | title=What, after All, Is Paleontology?
| journal=PALAIOS| volume=3 | issue=5 |date=October 1988 | page=453
| doi= 10.2307/3514718 | jstor=3514718
| bibcode=1988Palai...3..453L}}</ref>

=== Historical science ===
[[File:Europasaurus Praeparation.JPG|thumb|The preparation of the fossilised bones of ''[[Biology:Europasaurus|Europasaurus]] holgeri'']]

[[Biography:William Whewell|William Whewell]] (1794–1866) classified paleontology as one of the historical sciences, along with [[Earth:Archaeology|archaeology]], geology, [[Astronomy:Astronomy|astronomy]], [[Astronomy:Cosmology|cosmology]], [[Philology|philology]] and history itself:<ref>{{Cite book
| author=Laudan, R. | chapter=What's so Special about the Past? | page=58
| title=History and Evolution | editor=Nitecki, M.H. | editor2=Nitecki, D.V.  | date=1992
| chapter-url=https://books.google.com/books?id=kyLRtsvLS2AC&pg=PA55
| publisher=SUNY Press | isbn=0-7914-1211-3
| quote = To structure my discussion of the historical sciences, I shall borrow a way of analyzing them from the great Victorian philosopher of science, William Whewell [...]. [...] while his analysis of the historical sciences (or as Whewell termed them, the palaetiological sciences) will doubtless need to be modified, it provides a good starting point. Among them he numbered geology, paleontology, cosmogony, philology, and what we would term archaeology and history.
}}</ref> paleontology aims to describe phenomena of the past and to reconstruct their causes.<ref name="Cleland2002MethodologicalAndEpistemicDifferences">{{Cite journal|author= Cleland, C.E.|date= September 2002|title= Methodological and Epistemic Differences between Historical Science and Experimental Science|url= http://spot.colorado.edu/~cleland/articles/Cleland.PS.Pdf|url-status= dead|journal= Philosophy of Science|volume= 69|issue= 3|pages= 474–96|doi= 10.1086/342453|s2cid= 224835750|archive-url= https://web.archive.org/web/20081003221929/http://spot.colorado.edu/~cleland/articles/Cleland.PS.Pdf|archive-date= October 3, 2008|access-date= September 17, 2008}}</ref> Hence it has three main elements: description of past phenomena; developing a general theory about the causes of various types of change; and applying those theories to specific facts.<ref>{{Cite book
| author =Laudan, R. | chapter= What's so Special about the Past? | page= 58
| title= History and Evolution | editor= Nitecki, M.H. | editor2= Nitecki, D.V. | date= 1992
| chapter-url= https://books.google.com/books?id=kyLRtsvLS2AC&pg=PA55
| publisher= SUNY Press | isbn= 0-7914-1211-3
| quote = [Whewell] distinguished three tasks for such a historical science (1837 [...]): ' the Description of the facts and phenomena; – the general Theory of the causes of change appropriate to the case; – and the Application of the theory to the facts.'
}}</ref>
When trying to explain the past, paleontologists and other historical scientists often construct a set of one or more [[Hypothesis|hypotheses]] about the causes and then look for a "[[Philosophy:Smoking gun|smoking gun]]", a piece of evidence that strongly accords with one hypothesis over any others.<ref>
{{cite book
 | last1 = Perreault
 | first1 = Charles
 | chapter = The Search for Smoking Guns
 | title = The Quality of the Archaeological Record
 | url = https://books.google.com/books?id=TwyiDwAAQBAJ
 | location = Chicago
 | publisher = University of Chicago Press
 | date = 2019
 | page = 5
 | isbn = 978-0226631011
 | access-date = January 9, 2020
| quote = Historical scientists successfully learn about the past by employing a 'smoking-gun' approach. They start by formulating multiple, mutually exclusive hypotheses and then search for a "smoking gun" that discriminates between these hypotheses [...].
}}
</ref>
Sometimes researchers discover a "smoking gun" by a fortunate accident during other research. For example, the 1980 discovery by [[Biography:Luis Walter Alvarez|Luis]] and Walter Alvarez of [[Chemistry:Iridium|iridium]], a mainly extraterrestrial metal, in the [[Earth:Cretaceous|Cretaceous]]–[[Earth:Paleogene|Paleogene]] boundary layer made asteroid impact the most favored explanation for the [[Earth:Cretaceous–Paleogene extinction event|Cretaceous–Paleogene extinction event]] – although debate continues about the contribution of volcanism.<ref name="Cleland2002MethodologicalAndEpistemicDifferences" />

A complementary approach to developing scientific knowledge, experimental science,<ref>
{{cite web
 |url= https://ncse.ngo/creationism/analysis/historical-science-vs-experimental-science
 |title= 'Historical science' vs. 'experimental science'
 |date= October 25, 2019
|publisher= National Center for Science Education
 |access-date= January 9, 2020
|quote= Philosophers of science draw a distinction between research directed towards identifying laws and research which seeks to determine how particular historical events occurred. They do not claim, however, that the line between these sorts of science can be drawn neatly, and certainly do not agree that historical claims are any less empirically verifiable than other sorts of claims. [...] 'we can separate their two enterprises by distinguishing means from ends. The astronomer's problem is a historical one because the goal is to infer the properties of a particular object; the astronomer uses laws only as a means. Particle physics, on the other hand, is a nomothetic discipline because the goal is to infer general laws; descriptions of particular objects are only relevant as a means.'
 }}
</ref>
is often said{{by whom|date=January 2020}} to work by conducting experiments to ''disprove'' hypotheses about the workings and causes of natural phenomena. This approach cannot prove a hypothesis, since some later experiment may disprove it, but the accumulation of failures to disprove is often compelling evidence in favor. However, when confronted with totally unexpected phenomena, such as the first evidence for invisible [[Physics:Radiation|radiation]], experimental scientists often use the same approach as historical scientists: construct a set of hypotheses about the causes and then look for a "smoking gun".<ref name="Cleland2002MethodologicalAndEpistemicDifferences" />

=== Related sciences ===
{{Human timeline}}{{Life timeline}}
Paleontology lies between [[Biology:Biology|biology]] and geology since it focuses on the record of past life, but its main source of evidence is [[Biology:Fossil|fossil]]s in rocks.<ref>{{Cite encyclopedia|url=https://www.britannica.com/science/paleontology|title=paleontology {{!}} science|encyclopedia=Encyclopædia Britannica|access-date=August 24, 2017|language=en|url-status=live|archive-url=https://web.archive.org/web/20170824223403/https://www.britannica.com/science/paleontology|archive-date=August 24, 2017}}</ref><ref>{{Cite book | title=McGraw-Hill Encyclopedia of Science & Technology | publisher=McGraw-Hill | date=2002 | page=[https://archive.org/details/mcgrawhillencycl165newy/page/58 58] | isbn=0-07-913665-6 | url=https://archive.org/details/mcgrawhillencycl165newy/page/58 }}</ref> For historical reasons, paleontology is part of the geology department at many universities: in the 19th and early 20th centuries, geology departments found fossil evidence important for dating rocks, while biology departments showed little interest.<ref name="Laudan1992WhatSpecialP57">{{Cite book
| author=Laudan, R. | chapter=What's so Special about the Past? | page=57
| title=History and Evolution | editor=Nitecki, M.H. | editor2=Nitecki, D.V.  | date=1992
| publisher=SUNY Press | isbn=0-7914-1211-3
}}</ref>

Paleontology also has some overlap with [[Earth:Archaeology|archaeology]], which primarily works with objects made by humans and with human remains, while paleontologists are interested in the characteristics and evolution of humans as a species. When dealing with evidence about humans, archaeologists and paleontologists may work together&nbsp;– for example paleontologists might identify animal or plant fossils around an [[Social:Archaeological site|archaeological site]], to discover the people who lived there, and what they ate; or they might analyze the climate at the time of habitation.<ref name="UCMPfaqAnthro">{{cite web
 |url         = http://www.ucmp.berkeley.edu/faq.php#anthro
 |access-date  = September 17, 2008
|title       = How does paleontology differ from anthropology and archaeology?
 |publisher   = University of California Museum of Paleontology
 |url-status  = dead
 |archive-url  = https://web.archive.org/web/20080916013642/http://www.ucmp.berkeley.edu/faq.php#anthro
 |archive-date = September 16, 2008
}}</ref>

In addition, paleontology often borrows techniques from other sciences, including biology, [[Biology:Osteology|osteology]], ecology, [[Chemistry:Chemistry|chemistry]], [[Physics:Physics|physics]] and mathematics.<ref name="CowenHistLifeEd3Pxi" /> For example, [[Chemistry:Geochemistry|geochemical]] signatures from rocks may help to discover when life first arose on Earth,<ref name="BrasierMcLoughlinEtAl2006FreshLook">{{Cite journal
 |author          = Brasier, M.
 |author2         = McLoughlin, N.
 |author3         = Green, O.
 |author4         = Wacey, D.
 |name-list-style = amp
 |date            = June 2006
 |title           = A fresh look at the fossil evidence for early Archaean cellular life
 |journal         = [[Organization:Philosophical Transactions of the Royal Society B|Philosophical Transactions of the Royal Society B]]
 |volume          = 361
 |issue           = 1470
 |pages           = 887–902
 |doi             = 10.1098/rstb.2006.1835
 |url             = http://physwww.mcmaster.ca/~higgsp/3D03/BrasierArchaeanFossils.pdf
 |access-date      = August 30, 2008
|pmid            = 16754605
 |pmc             = 1578727
 |url-status=live
 |archive-url      = https://web.archive.org/web/20080911075352/http://physwww.mcmaster.ca/~higgsp/3D03/BrasierArchaeanFossils.pdf
 |archive-date     = September 11, 2008
}}</ref> and analyses of [[Chemistry:Carbon|carbon]] [[Physics:Isotope analysis|isotope ratios]] may help to identify climate changes and even to explain major transitions such as the [[Earth:Permian–Triassic extinction event|Permian–Triassic extinction event]].<ref name="Twitchett">{{Cite journal
|title=Rapid and synchronous collapse of marine and terrestrial ecosystems during the end-Permian biotic crisis
|author=Twitchett R.J.
|author2=Looy C.V.
|author3=Morante R.
|author4=Visscher H.
|author5=Wignall P.B. |journal=Geology |volume=29
|issue=4 |pages=351–54 |doi=10.1130/0091-7613(2001)029<0351:RASCOM>2.0.CO;2
|bibcode = 2001Geo....29..351T |year=2001
|s2cid=129908787
}}</ref> A relatively recent discipline, [[Biology:Molecular phylogenetics|molecular phylogenetics]], compares the [[Biology:DNA|DNA]] and [[Biology:RNA|RNA]] of modern organisms to re-construct the "family trees" of their evolutionary ancestors. It has also been used to estimate the dates of important evolutionary developments, although this approach is controversial because of doubts about the reliability of the "[[Biology:Molecular clock|molecular clock]]".<ref name="PetersonEtAl2005">{{Cite journal
| doi = 10.1073/pnas.0503660102 | pmid = 15983372 | author = Peterson, Kevin J. | author2 = Butterfield, N.J. | name-list-style = amp
| journal = Proceedings of the National Academy of Sciences | volume = 102 | issue = 27 | pages = 9547–52 | date = 2005
| title = Origin of the Eumetazoa: Testing ecological predictions of molecular clocks against the Proterozoic fossil record
| pmc = 1172262 | bibcode=2005PNAS..102.9547P
| doi-access = free }}</ref> Techniques from engineering have been used to analyse how the bodies of ancient organisms might have worked, for example the running speed and bite strength of ''[[Biology:Tyrannosaurus|Tyrannosaurus]],''<ref name="HutchinsonGarcia2002TrexSlow">{{Cite journal| author=Hutchinson, J.R.| author2=Garcia, M.| name-list-style=amp
| date=February 28, 2002 | title=''Tyrannosaurus'' was not a fast runner | journal=Nature | volume=415
| pages=1018–21 | doi=10.1038/4151018a | pmid=11875567 | issue=6875|bibcode = 2002Natur.415.1018H | s2cid=4389633| url=http://researchonline.rvc.ac.uk/id/eprint/1204/}}
Summary in press release [http://www.sciencenews.org/articles/20020302/fob1.asp No Olympian: Analysis hints ''T. Rex'' ran slowly, if at all] {{webarchive|url=https://web.archive.org/web/20080415183735/http://www.sciencenews.org/articles/20020302/fob1.asp |date=April 15, 2008 }}
</ref><ref name="MM03">{{Cite journal |last=Meers |first=M.B. |date=August 2003 |title=Maximum bite force and prey size of ''Tyrannosaurus rex'' and their relationships to the inference of feeding behavior |journal=Historical Biology |volume=16 |issue=1 |pages=1–12 |doi=10.1080/0891296021000050755 |s2cid=86782853 }}</ref> or the flight mechanics of ''Microraptor''.<ref name="MicroraptorWindTun">{{cite web|url=https://www.pbs.org/wgbh/nova/microraptor/liftdrag.html|title=The Four Winged Dinosaur: Wind Tunnel Test|publisher=Nova|access-date=June 5, 2010}}</ref> It is relatively commonplace to study the internal details of fossils using [[Astronomy:X-ray microtomography|X-ray microtomography]].<ref>{{cite journal|title=From clergymen to computers: the advent of virtual palaeontology|first1=Russell J.|last1=Garwood|first2=Imran A.|last2=Rahman|first3=Mark D. A.|last3=Sutton|year=2010|journal=Geology Today|volume=26|issue=3|pages=96–100|url=https://www.academia.edu/256386|access-date=June 16, 2015|doi=10.1111/j.1365-2451.2010.00753.x|bibcode=2010GeolT..26...96G |s2cid=53657220 }}</ref><ref name="SuttonRahman2013">{{cite book|author1=Mark Sutton|author2=Imran Rahman|author3=Russell Garwood|title=Techniques for Virtual Palaeontology|url=https://books.google.com/books?id=qYwKAgAAQBAJ|date=2013|publisher=Wiley|isbn=978-1-118-59125-3}}</ref> Paleontology, biology, archaeology, and [[Biology:Paleoneurobiology|paleoneurobiology]] combine to study endocranial casts (endocasts) of species related to humans to clarify the evolution of the human brain.<ref name="Bruner">{{cite journal|last=Bruner|first=Emiliano|title=Geometric morphometrics and palaeoneurology: brain shape evolution in the genus Homo|journal=Journal of Human Evolution|date=November 2004|volume=47|issue=5|pages=279–303|doi=10.1016/j.jhevol.2004.03.009|pmid=15530349}}</ref>

Paleontology even contributes to [[Astronomy:Astrobiology|astrobiology]], the investigation of possible life on other [[Astronomy:Planet|planet]]s, by developing models of how life may have arisen and by providing techniques for detecting evidence of life.<ref>{{Cite journal
| title=Astrobiology: A New Frontier for 21st Century Paleontologists | author=Cady, S.L.
| journal=PALAIOS| volume=13 | issue=2  |date=April 1998 | pages=95–97
| doi=10.2307/3515482
| pmid=11542813 | jstor=3515482
| bibcode=1998Palai..13...95C}}</ref>

=== Subdivisions ===
As knowledge has increased, paleontology has developed specialised subdivisions.<ref>{{Cite journal | author=Plotnick, R.E. | title=A Somewhat Fuzzy Snapshot of Employment in Paleontology in the United States | journal=Palaeontologia Electronica | publisher=Coquina Press | volume=11 | issue=1 | issn=1094-8074 | url=http://palaeo-electronica.org/2008_1/commentary/comment.htm | access-date=September 17, 2008 | url-status=live | archive-url=https://web.archive.org/web/20080518081827/http://palaeo-electronica.org/2008_1/commentary/comment.htm | archive-date=May 18, 2008 }}</ref> Vertebrate paleontology concentrates on fossils from the earliest fish to the immediate ancestors of modern [[Biology:Mammal|mammal]]s. Invertebrate paleontology deals with fossils such as [[Biology:Mollusc|mollusc]]s, [[Biology:Arthropod|arthropod]]s, [[Biology:Annelid|annelid]] worms and [[Biology:Echinoderm|echinoderm]]s. [[Biology:Paleobotany|Paleobotany]] studies fossil [[Biology:Embryophyte|plants]], [[Biology:Algae|algae]], and fungi. [[Earth:Palynology|Palynology]], the study of [[Biology:Pollen|pollen]] and spores produced by land plants and [[Biology:Protist|protist]]s, straddles paleontology and [[Biology:Botany|botany]], as it deals with both living and fossil organisms. [[Biology:Micropaleontology|Micropaleontology]] deals with microscopic fossil organisms of all kinds.<ref name="UCMPpaleoSpecialisms">{{cite web | url=http://www.ucmp.berkeley.edu/FAQ/whatispaleo.html | access-date=September 17, 2008 | title=What is Paleontology? | publisher=University of California Museum of Paleontology | url-status=dead | archive-url=https://web.archive.org/web/20080803042642/http://www.ucmp.berkeley.edu/FAQ/whatispaleo.html | archive-date=August 3, 2008 }}</ref>
[[File:Fossil Tyranausaurus Rex at the Royal Tyrell Museum, Alberta, Canada.jpg|thumb|upright|left| Analyses using engineering techniques show that ''Tyrannosaurus'' had a devastating bite, but raise doubts about its running ability.]]
Instead of focusing on individual organisms, [[Earth:Paleoecology|paleoecology]] examines the interactions between different ancient organisms, such as their food chains, and the two-way interactions with their environments.<ref>{{Cite journal | author=Kitchell, J.A. | title=Evolutionary Paleocology: Recent Contributions to Evolutionary Theory | journal=Paleobiology | volume=11 | issue=1 | date=1985 | pages=91–104 | url=http://www.ucmp.berkeley.edu/FAQ/whatispaleo.html | access-date=September 17, 2008 | url-status=dead | archive-url=https://web.archive.org/web/20080803042642/http://www.ucmp.berkeley.edu/FAQ/whatispaleo.html | archive-date=August 3, 2008 | doi=10.1017/S0094837300011428 | bibcode=1985Pbio...11...91K | s2cid=88584416 }}</ref>&nbsp; For example, the development of [[Chemistry:Oxygen#Photosynthesis and respiration|oxygenic photosynthesis]] by bacteria caused the [[Chemistry:Oxygen#Build-up in the atmosphere|oxygenation of the atmosphere]] and hugely increased the productivity and diversity of [[Earth:Ecosystem|ecosystem]]s.<ref name="Hoehler">{{Cite journal| title=The role of microbial mats in the production of reduced gases on the early Earth
| author=Hoehler, T.M.
| author2=Bebout, B.M.
| author3=Des Marais, D.J.
| name-list-style=amp | journal=Nature | volume=412
| pages=324–27 | date=July 19, 2001 | doi=10.1038/35085554
| pmid=11460161 | issue=6844
| bibcode=2001Natur.412..324H
| s2cid=4365775
}}</ref> Together, these led to the evolution of complex eukaryotic cells, from which all multicellular organisms are built.<ref name="HedgesBlairEtAl2004molecularTimescaleOfEukaryoteEvolution">{{Cite journal
 |title           = A molecular timescale of eukaryote evolution and the rise of complex multicellular life
 |author          = Hedges, S.B.
 |author2         = Blair, J.E
 |author3         = Venturi, M.L.
 |author4         = Shoe, J.L.
 |name-list-style = amp
 |journal         = BMC Evolutionary Biology
 |volume          = 4
 |doi             = 10.1186/1471-2148-4-2
 |date            = January 2004
 |page            = 2
 |pmid            = 15005799
 |pmc             = 341452
|doi-access = free
 }}</ref>

[[Earth:Paleoclimatology|Paleoclimatology]], although sometimes treated as part of paleoecology,<ref name="UCMPpaleoSpecialisms" /> focuses more on the history of Earth's climate and the mechanisms that have changed it<ref>{{cite web
 |url        = http://matrix.geology.ohio-state.edu/ProspectiveGradStudents/school-of-earth-sciences-directory/specialties/global-and-environmental-change/paleoclimatology
 |archive-url = https://web.archive.org/web/20071109175527/http://matrix.geology.ohio-state.edu/ProspectiveGradStudents/school-of-earth-sciences-directory/specialties/global-and-environmental-change/paleoclimatology
 |url-status=dead
 |archive-date = November 9, 2007
|title      = Paleoclimatology
 |publisher  = Ohio State University
 |access-date = September 17, 2008
}}</ref>&nbsp;– which have sometimes included [[Biology:Evolution|evolution]]ary developments, for example the rapid expansion of land plants in the [[Earth:Devonian|Devonian]] period removed more [[Chemistry:Carbon dioxide|carbon dioxide]] from the atmosphere, reducing the [[Earth:Greenhouse effect|greenhouse effect]] and thus helping to cause an [[Earth:Ice age|ice age]] in the [[Earth:Carboniferous|Carboniferous]] period.<ref name="AlgeoScheckler1998errestrialMarineTeleconnectionsInDevonian">{{Cite journal
| author=Algeo, T.J.
| author2=Scheckler, S.E.
| name-list-style=amp
| title=Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events
| journal=Philosophical Transactions of the Royal Society B | date=1998 | volume=353 | pages=113–30
| doi=10.1098/rstb.1998.0195 | pmc=1692181
| issue=1365
}}</ref>

[[Earth:Biostratigraphy|Biostratigraphy]], the use of fossils to work out the chronological order in which rocks were formed, is useful to both paleontologists and geologists.<ref>{{cite web
 |url         = http://evolution.berkeley.edu/evosite/history/biostratigraphy.shtml
 |access-date  = September 17, 2008
|title       = Biostratigraphy: William Smith
 |url-status=dead
 |archive-url  = https://web.archive.org/web/20080724091521/http://evolution.berkeley.edu/evosite/history/biostratigraphy.shtml
 |archive-date = July 24, 2008
}}</ref> [[Earth:Biogeography|Biogeography]] studies the spatial distribution of organisms, and is also linked to geology, which explains how Earth's geography has changed over time.<ref>{{cite web
 |url         = http://evolution.berkeley.edu/evosite/history/biogeography.shtml
 |access-date  = September 17, 2008
|title       = Biogeography: Wallace and Wegener (1 of 2)
 |publisher   = University of California Museum of Paleontology and University of California at Berkeley
 |url-status=dead
 |archive-url  = https://web.archive.org/web/20080515204649/http://evolution.berkeley.edu/evosite/history/biogeography.shtml
 |archive-date = May 15, 2008
}}</ref>
<!-- *********** commented out as unreferenced
Modern paleontology sets ancient life in its context by studying how long-term physical changes of global geography [[Earth:Palaeogeography|paleogeography]] and climate paleoclimate have affected the [[Biology:Evolution|evolution]] of life, how ecosystems have responded to these changes and have adapted the planetary environment in turn and how these mutual responses have affected today's patterns of [[Biology:Biodiversity|biodiversity]]. Hence, paleontology overlaps with geology (the study of rocks and rock formations) as well as with [[Biology:Botany|botany]], [[Biology:Biology|biology]], [[Biology:Zoology|zoology]] and ecology&nbsp;– fields concerned with life forms and how they interact.

The major subdivisions of paleontology include [[Biology:Paleozoology|paleozoology]] (animals), [[Biology:Paleobotany|paleobotany]] (plants) and [[Biology:Micropaleontology|micropaleontology]] (microfossils). Paleozoologists may specialise in invertebrate paleontology, which deals with animals without backbones or in vertebrate palaeontology, dealing with fossils of animals with backbones, including fossil hominids (palaeoanthropology). Micropaleontologists study microscopic fossils, including organic-walled microfossils whose study is called [[Earth:Palynology|palynology]].

There are many developing specialities such as [[Biology:Paleobiology|paleobiology]], [[Earth:Paleoecology|paleoecology]], [[Biology:Ichnology|ichnology]] (the study of tracks and burrows) and [[Earth:Taphonomy|taphonomy]] (the study of what happens to organisms after they expire). Major areas of study include the correlation of rock strata with their geologic ages and the study of evolution of lifeforms.

Paleontology uses the same classic [[Biology:Binomial nomenclature|binomial nomenclature]] scheme, devised for the biology of living things by the mid-18th century Swedish biologist Carolus Linnaeus and increasingly sets these species in a genealogical framework, showing their degrees of interrelatedness using the still somewhat controversial technique of '[[Biology:Cladistics|cladistics]]'.

The primary economic importance of paleontology lies in the use of fossils to determine the age and nature of the rocks that contain them or the layers above or below. This information is vital to the mining industry and especially the petroleum industry. Simply looking at the fossils contained in a rock remains one of the fastest and most accurate means of telling how old that rock is.

Fossils were known by primitive humans and were sometimes identified correctly as the remains of ancient lifeforms. The organised study of paleontology dates from the late 18th century. For a more complete historical overview see the article History of paleontology.
***********  -->

== Sources of evidence ==

=== Body fossils ===
{{Main|Biology:Fossil}}
[[File:Marrella (fossil).png|thumb|left| This ''[[Biology:Marrella|Marrella]]'' specimen illustrates how clear and detailed the fossils from the Burgess Shale lagerstätte are.]]
Fossils of organisms' bodies are usually the most informative type of evidence. The most common types are wood, bones, and shells.<ref name="UCMPWhatIsPaleo">{{cite web | url=http://www.ucmp.berkeley.edu/faq.php#paleo | access-date=September 17, 2008 | title=What is paleontology? | publisher=University of California Museum of Paleontology | url-status=dead | archive-url=https://web.archive.org/web/20080916013642/http://www.ucmp.berkeley.edu/faq.php#paleo | archive-date=September 16, 2008 }}</ref> Fossilisation is a rare event, and most fossils are destroyed by [[Earth:Erosion|erosion]] or [[Earth:Metamorphism|metamorphism]] before they can be observed. Hence the fossil record is very incomplete, increasingly so further back in time. Despite this, it is often adequate to illustrate the broader patterns of life's history.<ref name="BentonQualityFossilRecord">{{Cite journal|author=Benton M.J.|author2=Wills M.A.|author3=Hitchin R.
|title=Quality of the fossil record through time |journal=Nature |volume=403 |issue=6769 |pages=534–37
|date=2000 |pmid=10676959 |doi=10.1038/35000558|bibcode = 2000Natur.403..534B |s2cid=4407172|url=http://doc.rero.ch/record/13615/files/PAL_E635.pdf }}
: Non-technical [http://palaeo.gly.bris.ac.uk/cladestrat/news.html summary] {{webarchive|url=https://web.archive.org/web/20070809045303/http://palaeo.gly.bris.ac.uk/cladestrat/news.html |date=August 9, 2007 }}
</ref> There are also biases in the fossil record: different environments are more favorable to the preservation of different types of organism or parts of organisms.<ref name="Butterfield2003ExceptionalFossilPreservation">{{Cite journal | author = Butterfield, N.J. | date = 2003 | title = Exceptional Fossil Preservation and the Cambrian Explosion | journal = Integrative and Comparative Biology | volume = 43 | issue = 1 | pages = 166–77 | doi = 10.1093/icb/43.1.166 | pmid = 21680421 | doi-access = free }}</ref> Further, only the parts of organisms that were already mineralised are usually preserved, such as the shells of molluscs. Since most animal species are soft-bodied, they decay before they can become fossilised. As a result, although there are 30-plus [[Biology:Phylum|phyla]] of living animals, two-thirds have never been found as fossils.<ref name="CowenHistLifeEd3Pxi" />

Occasionally, unusual environments may preserve soft tissues.<ref name="Anderson2023FossilChemicalFramework">{{Cite journal | author = Anderson, L.A. | date = 2023 | title = A chemical framework for the preservation of fossil vertebrate cells and soft tissues | journal = Earth-Science Reviews | volume = 240 | pages = 104367 | doi = 10.1016/j.earscirev.2023.104367 | bibcode = 2023ESRv..24004367A | doi-access = free }}</ref> These lagerstätten allow paleontologists to examine the internal anatomy of animals that in other sediments are represented only by shells, spines, claws, etc.&nbsp;– if they are preserved at all. However, even lagerstätten present an incomplete picture of life at the time. The majority of organisms living at the time are probably not represented because lagerstätten are restricted to a narrow range of environments, e.g. where soft-bodied organisms can be preserved very quickly by events such as mudslides; and the exceptional events that cause quick burial make it difficult to study the normal environments of the animals.<ref>{{Cite journal | author = Butterfield, N.J. | date = 2001 | title = Ecology and evolution of Cambrian plankton | journal = The Ecology of the Cambrian Radiation | publisher = Columbia University Press | location = New York | pages = 200–16 | url = http://webcache.googleusercontent.com/scholar?hl=en&lr=&ie=UTF-8&q=cache:9xeRu1SdF0QJ:www.earthscape.org/r3/ES14785/ch09.pdf+ | access-date = September 27, 2007 }}{{Dead link|date=January 2019 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> The sparseness of the fossil record means that organisms are expected to exist long before and after they are found in the fossil record&nbsp;– this is known as the Signor–Lipps effect.<ref name="Signor1982">{{Cite journal
 |author       = Signor, P.W.
 |date         = 1982
 |title        = Sampling bias, gradual extinction patterns and catastrophes in the fossil record
 |journal      = Geological Implications of Impacts of Large Asteroids and Comets on the Earth
 |series       = Geological Society of America Special Papers
 |volume       = 190
 |id           = A 84–25651 10–42
 |location     = Boulder, CO
 |publisher    = Geological Society of America
 |pages        = 291–96
 |doi          = 10.1130/SPE190-p291
 |isbn         = 0-8137-2190-3
 |url          = http://www.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=A8425675AH
 |access-date  = January 1, 2008
 |archive-date = July 28, 2020
 |archive-url  = https://web.archive.org/web/20200728044012/https://about.proquest.com/
 |url-status   = dead
}}</ref>

=== Trace fossils ===
[[File:CambrianRusophycus.jpg|thumb|Cambrian trace fossils including ''Rusophycus'', made by a trilobite]]
[[File:Climactichnites ToddGass3.jpg|thumb|''[[Biology:Climactichnites|Climactichnites]]'' — Cambrian trackways (10–12 cm wide) from large, slug-like animals on a Cambrian tidal flat in what is now Wisconsin]]
{{Main|Biology:Trace fossil}}

[[Biology:Trace fossil|Trace fossil]]s consist mainly of tracks and burrows, but also include coprolites (fossil [[Biology:Feces|feces]]) and marks left by feeding.<ref name="UCMPWhatIsPaleo" /><ref name="FedonkinGehlingEtAl2007RiseOfAnimals" /> Trace fossils are particularly significant because they represent a data source that is not limited to animals with easily fossilised hard parts, and they reflect organisms' behaviours. Also many traces date from significantly earlier than the body fossils of animals that are thought to have been capable of making them.<ref name="Seilacher1994">e.g. {{Cite journal
| author = Seilacher, A. | date = 1994 | title = How valid is Cruziana Stratigraphy?
| journal = International Journal of Earth Sciences | volume = 83 | issue = 4 | pages = 752–58
| bibcode = 1994GeoRu..83..752S
| doi = 10.1007/BF00251073| s2cid = 129504434 }}</ref> Whilst exact assignment of trace fossils to their makers is generally impossible, traces may for example provide the earliest physical evidence of the appearance of moderately complex animals (comparable to [[Biology:Earthworm|earthworm]]s).<ref name="FedonkinGehlingEtAl2007RiseOfAnimals">{{Cite book
| author=Fedonkin, M.A.
| author2=Gehling, J.G.
| author3=Grey, K.
| author4=Narbonne, G.M.
| author5=Vickers-Rich, P.
| title=The Rise of Animals: Evolution and Diversification of the Kingdom Animalia
| publisher=JHU Press | date=2007 | isbn=978-0-8018-8679-9 | pages=213–16
| url=https://books.google.com/books?id=OFKG6SmPNuUC&pg=PA213
}}</ref>

=== Geochemical observations ===
{{Main|Chemistry:Geochemistry}}
Geochemical observations may help to deduce the global level of biological activity at a certain period, or the affinity of certain fossils. For example, geochemical features of rocks may reveal when life first arose on Earth,<ref name="BrasierMcLoughlinEtAl2006FreshLook" /> and may provide evidence of the presence of eukaryotic cells, the type from which all multicellular organisms are built.<ref name="BrocksLoganEtAl1999RiseOfEukaryotes">{{Cite journal
 |author          = Brocks, J.J.
 |author2         = Logan, G.A.
 |author3         = Buick, R.
 |author4         = Summons, R.E.
 |name-list-style = amp
 |date            = 1999
 |title           = Archaean molecular fossils and the rise of eukaryotes
 |journal         = Science
 |volume          = 285
 |pages           = 1033–36
 |doi             = 10.1126/science.285.5430.1033
 |pmid            = 10446042
 |issue           = 5430
 |bibcode = 1999Sci...285.1033B
 |s2cid = 11028394
}}</ref> Analyses of [[Chemistry:Carbon|carbon]] [[Physics:Isotope analysis|isotope ratios]] may help to explain major transitions such as the [[Earth:Permian–Triassic extinction event|Permian–Triassic extinction event]].<ref name="Twitchett" />

== Classifying ancient organisms ==

[[File:Biological classification L Pengo.svg| thumb | left | upright=0.45 | Levels in the [[Linnaean taxonomy|Linnaean taxonomy]]]]
Naming groups of organisms in a way that is clear and widely agreed is important, as some disputes in paleontology have been based just on misunderstandings over names.<ref name="BrochuSumrall2001">{{Cite journal
| author=Brochu, C.A
| author2=Sumrall, C.D.
| name-list-style=amp
| title=Phylogenetic Nomenclature and Paleontology
| journal=Journal of Paleontology | volume=75 | issue=4 |date=July 2001 | pages=754–57
| doi=10.1666/0022-3360(2001)075<0754:PNAP>2.0.CO;2 | jstor=1306999
| s2cid=85927950
| issn=0022-3360
| url=http://doc.rero.ch/record/14974/files/PAL_E2123.pdf
}}</ref> [[Linnaean taxonomy]] is commonly used for classifying living organisms, but runs into difficulties when dealing with newly discovered organisms that are significantly different from known ones. For example: it is hard to decide at what level to place a new higher-level grouping, e.g. [[Biology:Genus|genus]] or family or [[Biology:Order|order]]; this is important since the Linnaean rules for naming groups are tied to their levels, and hence if a group is moved to a different level it must be renamed.<ref>{{Cite book
| author=Ereshefsky, M.
| page=5
| title=The Poverty of the Linnaean Hierarchy: A Philosophical Study of Biological Taxonomy
| publisher= Cambridge University Press | date=2001 | isbn=0-521-78170-1
| url=https://books.google.com/books?id=tM6E8-_vSD0C&pg=PP1
}}</ref>

<div style="width:auto; border:solid 1px silver; padding:2px; margin:2px; float:right; font-size:90%">
<div style="width:auto; border:solid 1px silver; padding:5px">
{{clade
   |label1=[[Biology:Tetrapod|Tetrapod]]s
   |1={{clade
         |1=[[Biology:Amphibian|Amphibian]]s
         |label2=[[Biology:Amniote|Amniote]]s
         |2={{clade
               |label1=[[Biology:Synapsid|Synapsid]]s
               |1={{clade
                      |1=Extinct Synapsids
                      |label2={{font color|yellow|red|&nbsp;&nbsp;&nbsp;}}
                      |2=[[Biology:Mammal|Mammal]]s
                   }}
               |label2=Reptiles
               |2={{clade
                     |1=Extinct reptiles
                     |2=Lizards and snakes
                     |label3=[[Biology:Archosaur|Archosaur]]s
                     |3={{clade
                          |1=Extinct<br />Archosaurs
                          |2=Crocodilians
                          |label3=Dinosaurs<br />{{font color|yellow|red|&nbsp;'''?'''&nbsp;}}
                          |3={{clade
                                 |1=Extinct<br />Dinosaurs
                                 |label2=<br />{{font color|yellow|red|&nbsp;'''?'''&nbsp;}}
                                 |2=Birds
                              }}
                        }}
                  }}
            }}
       }}
}}
</div>'''Simple example cladogram'''<br />{{bg|red|&nbsp;&nbsp;&nbsp;}} Warm-bloodedness evolved somewhere in the<br />synapsid–mammal transition.<br />{{font color|yellow|red|&nbsp;'''?'''&nbsp;}} Warm-bloodedness must also have evolved at one of<br /> these points&nbsp;– an example of [[Biology:Convergent evolution|convergent evolution]].<ref name="CowenHistLifeEd3Pxi" /></div>
Paleontologists generally use approaches based on [[Biology:Cladistics|cladistics]], a technique for working out the evolutionary "family tree" of a set of organisms.<ref name="BrochuSumrall2001" /> It works by the logic that, if groups B and C have more similarities to each other than either has to group A, then B and C are more closely related to each other than either is to A. Characters that are compared may be [[Biology:Anatomy|anatomical]], such as the presence of a notochord, or molecular, by comparing sequences of [[Biology:DNA|DNA]] or [[Biology:Protein|protein]]s. The result of a successful analysis is a hierarchy of clades&nbsp;– groups that share a common ancestor. Ideally the "family tree" has only two branches leading from each node ("junction"), but sometimes there is too little information to achieve this, and paleontologists have to make do with junctions that have several branches. The cladistic technique is sometimes fallible, as some features, such as wings or [[Biology:Evolution of the eye|camera eyes]], evolved more than once, [[Biology:Convergent evolution|convergently]]&nbsp;– this must be taken into account in analyses.<ref name="CowenHistLifeEd3Pxi" />

[[Biology:Evolutionary developmental biology|Evolutionary developmental biology]], commonly abbreviated to "Evo Devo", also helps paleontologists to produce "family trees", and understand fossils.<ref name=Tetrop>{{cite journal|title=A Paleozoic Stem Group to Mite Harvestmen Revealed through Integration of Phylogenetics and Development|first1=Russell J.|last1=Garwood|first2=Prashant P.|last2=Sharma|first3=Jason A.|last3=Dunlop|first4=Gonzalo|last4=Giribet|author4-link=Gonzalo Giribet|year=2014|journal=Current Biology|volume=24|issue=9|pages=1017–23|doi=10.1016/j.cub.2014.03.039|pmid=24726154|doi-access=free}}</ref> For example, the embryological development of some modern [[Biology:Brachiopod|brachiopod]]s suggests that brachiopods may be descendants of the [[Biology:Halkieriid|halkieriid]]s, which became extinct in the [[Earth:Cambrian|Cambrian]] period.<ref>{{Cite journal | author=Cohen, B.L. | author2=Holmer, L.E. | author3=Luter, C. | name-list-style=amp | date=2003 | title=The brachiopod fold: a neglected body plan hypothesis | journal=Palaeontology | volume=46 | issue=1 | pages=59–65 | doi=10.1111/1475-4983.00287 | bibcode=2003Palgy..46...59C | doi-access=free }}</ref>
{{Clear}}

== Estimating the dates of organisms ==
{{Main|Physics:Geochronology}}
{{Annotated image|caption=Common index fossils used to date rocks in the northeast United States|image=Index fossils blank 01.png | width=332
| style="height:261px;"| image-width=338 | image-left=0 | image-top=0 | float=right | annot-font-size=9
| annotations =
<!-- eras -->
{{Annotation|1|15|[[Earth:Cenozoic|Cenozoic]]}}
{{Annotation|1|70|[[Earth:Mesozoic|Mesozoic]]}}
{{Annotation|1|165|[[Earth:Paleozoic|Paleozoic]]}}
{{Annotation|1|252|[[Earth:Proterozoic|Proterozoic]]}}
<!-- periods -->
{{Annotation|57|0|[[Earth:Quaternary|Quater-<br />nary]]}}
{{Annotation|57|25|[[Earth:Tertiary|Tertiary]]}}
{{Annotation|57|42|[[Earth:Cretaceous|Creta-<br />ceous]]}}
{{Annotation|57|68|[[Earth:Jurassic|Jurassic]]}}
{{Annotation|57|89|[[Earth:Triassic|Triassic]]}}
{{Annotation|57|109|[[Earth:Permian|Permian]]}}
{{Annotation|57|122|Missis-<br />sippian}}
{{Annotation|57|146|Pennsyl-<br />vanian}}
{{Annotation|57|166|[[Earth:Devonian|Devo-<br />nian]]}}
{{Annotation|57|191|[[Earth:Silurian|Silurian]]}}
{{Annotation|57|207|[[Earth:Ordovician|Ordo-<br />vician]]}}
{{Annotation|57|227|[[Earth:Cambrian|Camb-<br />rian]]}}
<!-- fossils: left col -->
{{Annotation|112|2|''[[Biology:Pecten (bivalve)|Pecten gibbus]]''}}
{{Annotation|120|20|''Calyptraphorus<br />velatus''}}
{{Annotation|125|40|''Scaphites<br />hippocrepis''}}
{{Annotation|129|63|''[[Biology:Perisphinctes|Perisphinctes]]<br />tiziani''}}
{{Annotation|125|83|''Tropites<br />subbullatus''}}
{{Annotation|123|105|''Leptodus<br />americanus''}}
{{Annotation|110|125|''Cactocrinus<br />multibrachiatus''}}
{{Annotation|128|143|''Dictyoclostus<br />americanus''}}
{{Annotation|99|166|''[[Biology:Mucrospirifer mucronatus|Mucrospirifer<br />mucronatus]]''}}
{{Annotation|125|186|''Cystiphyllum<br />niagarense''}}
{{Annotation|105|211|''Bathyurus extans''}}
{{Annotation|127|231|''[[Biology:Paradoxides|Paradoxides]] pinus''}}
<!-- fossils: rightcol -->
{{Annotation|225|6|''[[Biology:Neptunea|Neptunea]] tabulata''}}
{{Annotation|257|20|''[[Biology:Venericardia|Venericardia]]<br />planicosta''}}
{{Annotation|249|40|''[[Biology:Inoceramus|Inoceramus]]<br />labiatus''}}
{{Annotation|253|63|''[[Biology:Nerinea|Nerinea]] trinodosa''}}
{{Annotation|252|82|''Monotis<br />subcircularis''}}
{{Annotation|275|103|''[[Biology:Parafusulina|Parafusulina]]<br />bosei''}}
{{Annotation|230|123|''Lophophyllidium<br />proliferum''}}
{{Annotation|255|143|''Prolecanites gurleyi''}}
{{Annotation|240|165|''Palmatolepus<br />unicornis''}}
{{Annotation|251|185|''Hexamocaras hertzeri''}}
{{Annotation|250|206|''[[Biology:Tetragraptus|Tetragraptus]] fructicosus''}}
{{Annotation|260|226|''Billingsella corrugata''}}
}}
Paleontology seeks to map out how living things have changed through time. A substantial hurdle to this aim is the difficulty of working out how old fossils are. Beds that preserve fossils typically lack the radioactive elements needed for [[Physics:Radiometric dating|radiometric dating]]. This technique is our only means of giving rocks greater than about 50 million years old an absolute age,<!--<ref group=note>Astrochronology can date sediments back to the Eocene{{Confusing|date=May 2012}}</ref> the link for this note appears not to work --> and can be accurate to within 0.5% or better.<ref name="Martin2000">{{Cite journal
| author = Martin, M.W.
| date = May 5, 2000
| title = Age of Neoproterozoic Bilaterian Body and Trace Fossils, White Sea, Russia: Implications for Metazoan Evolution
| journal = Science | volume = 288
| issue = 5467 | pages = 841–45 | doi = 10.1126/science.288.5467.841 | type = abstract | pmid = 10797002
|bibcode = 2000Sci...288..841M |s2cid=1019572 }}</ref> Although radiometric dating requires very careful laboratory work, its basic principle is simple: the rates at which various radioactive elements [[Physics:Radioactive decay|decay]] are known, and so the ratio of the radioactive element to the element into which it decays shows how long ago the radioactive element was incorporated into the rock. Radioactive elements are common only in rocks with a volcanic origin, and so the only fossil-bearing rocks that can be dated radiometrically are a few volcanic ash layers.<ref name="Martin2000" />

Consequently, paleontologists must usually rely on [[Earth:Stratigraphy|stratigraphy]] to date fossils. Stratigraphy is the science of deciphering the "layer-cake" that is the [[Earth:Sediment|sediment]]ary record, and has been compared to a jigsaw puzzle.<ref>{{Cite journal
| author=Pufahl, P.K.
| author2=Grimm, K.A.
| author3=Abed, A.M.
| author4=Sadaqah, R.M.Y.
| name-list-style=amp
| title=Upper Cretaceous (Campanian) phosphorites in Jordan: implications for the formation of a south Tethyan phosphorite giant
| journal=Sedimentary Geology | volume=161 |date=October 2003 | pages=175–205
| doi=10.1016/S0037-0738(03)00070-8 | issue=3–4 | bibcode=2003SedG..161..175P}}</ref> Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, the fossil's age must lie between the two known ages.<ref>{{cite web | url=http://pubs.usgs.gov/gip/geotime/radiometric.html | access-date=September 20, 2008 | title=Geologic Time: Radiometric Time Scale | publisher=U.S. Geological Survey | url-status=live | archive-url=https://web.archive.org/web/20080921135337/http://pubs.usgs.gov/gip/geotime/radiometric.html | archive-date=September 21, 2008 }}</ref> Because rock sequences are not continuous, but may be broken up by [[Earth:Fault (geology)|faults]] or periods of [[Earth:Erosion|erosion]], it is very difficult to match up rock beds that are not directly next to one another. However, fossils of species that survived for a relatively short time can be used to link up isolated rocks: this technique is called ''biostratigraphy''. For instance, the conodont ''Eoplacognathus pseudoplanus'' has a short range in the Middle Ordovician period.<ref>{{Cite journal
| author = Löfgren, A. | date = 2004
| title = The conodont fauna in the Middle Ordovician ''Eoplacognathus pseudoplanus'' Zone of Baltoscandia
| journal = Geological Magazine | volume = 141 | issue = 4 | pages = 505–24
| doi = 10.1017/S0016756804009227 | bibcode = 2004GeoM..141..505L| s2cid = 129600604
}}</ref> If rocks of unknown age are found to have traces of ''E. pseudoplanus'', they must have a mid-Ordovician age. Such index fossils must be distinctive, be globally distributed and have a short time range to be useful. However, misleading results are produced if the index fossils turn out to have longer fossil ranges than first thought.<ref name="Gehling2001" /> Stratigraphy and biostratigraphy can in general provide only relative dating (''A'' was before ''B''), which is often sufficient for studying evolution. However, this is difficult for some time periods, because of the problems involved in matching up rocks of the same age across different [[Earth:Continent|continent]]s.<ref name="Gehling2001">{{Cite journal | last1 = Gehling | first1 = James | last2 = Jensen | first2 = Sören | last3 = Droser | first3 = Mary | last4 = Myrow | first4 = Paul | last5 = Narbonne | first5 = Guy | title = Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland | journal = Geological Magazine | volume = 138 | issue = 2 | pages = 213–18 | date = March 2001 | doi = 10.1017/S001675680100509X | bibcode = 2001GeoM..138..213G | s2cid = 131211543 }}</ref>

Family-tree relationships may also help to narrow down the date when lineages first appeared. For instance, if fossils of B or C date to X&nbsp;million years ago and the calculated "family tree" says A was an ancestor of B and C, then A must have evolved more than X&nbsp;million years ago.

It is also possible to estimate how long ago two living clades diverged&nbsp;– i.e. approximately how long ago their last common ancestor must have lived&nbsp;– by assuming that DNA [[Biology:Mutation|mutation]]s accumulate at a constant rate. These "[[Biology:Molecular clock|molecular clock]]s", however, are fallible, and provide only a very approximate timing: for example, they are not sufficiently precise and reliable for estimating when the groups that feature in the [[Earth:Cambrian explosion|Cambrian explosion]] first evolved,<ref>{{Cite journal
| author=Hug, L.A.
| author2=Roger, A.J.
| name-list-style=amp
| title=The Impact of Fossils and Taxon Sampling on Ancient Molecular Dating Analyses
| journal=Molecular Biology and Evolution | date=2007 | volume=24 | issue=8 | pages=889–1897
| doi=10.1093/molbev/msm115 | pmid=17556757
| doi-access=free
}}</ref> and estimates produced by different techniques may vary by a factor of two.<ref name="PetersonEtAl2005" />

== History of life ==
[[File:Runzelmarken.jpg|thumb|This wrinkled "elephant skin" texture is a trace fossil of a non-stromatolite [[Biology:Microbial mat|microbial mat]]. The image shows the location, in the Burgsvik beds of Sweden, where the texture was first identified as evidence of a microbial mat.<ref name="Manten1966">
{{Cite journal | author = Manten, A.A. | date = 1966 | title = Some problematic shallow-marine structures | journal = Marine Geol. | volume = 4 | pages = 227–32 | doi = 10.1016/0025-3227(66)90023-5 | url = http://igitur-archive.library.uu.nl/geo/2006-1213-210452/UUindex.html | access-date = June 18, 2007 | issue = 3 | url-status=dead | archive-url = https://web.archive.org/web/20081021003026/http://igitur-archive.library.uu.nl/geo/2006-1213-210452/UUindex.html | archive-date = October 21, 2008 | bibcode = 1966MGeol...4..227M | hdl = 1874/16526 | s2cid = 129854399 | hdl-access = free }}</ref>]]
{{Main|Biology:Evolutionary history of life}}
Earth formed about {{ma|4570}} and, after a collision that formed the [[Astronomy:Moon|Moon]] about 40 million years later, may have cooled quickly enough to have oceans and an atmosphere about {{ma|4440}}.<ref>{{cite web | title = Early Earth Likely Had Continents And Was Habitable | date = November 17, 2005 | url = http://www.colorado.edu/news/releases/2005/438.html | url-status=dead | archive-url = https://web.archive.org/web/20081014081528/http://www.colorado.edu/news/releases/2005/438.html | archive-date = October 14, 2008 }}</ref><ref>{{Cite journal | author1= A.J. Cavosie | author2 = J.W. Valley |author3= S.A. Wilde | author4 = E.I.M.F. | name-list-style = amp | date = July 15, 2005 | title = Magmatic δ<sup>18</sup>O in 4400–3900 Ma detrital zircons: A record of the alteration and recycling of crust in the Early Archean | journal = Earth and Planetary Science Letters | volume = 235 | issue = 3–4 | pages = 663–81 | doi = 10.1016/j.epsl.2005.04.028 | bibcode = 2005E&PSL.235..663C }}</ref> There is evidence on the Moon of a [[Astronomy:Late Heavy Bombardment|Late Heavy Bombardment]] by asteroids from {{ma|4000|3800}}. If, as seems likely, such a bombardment struck Earth at the same time, the first atmosphere and oceans may have been stripped away.<ref>{{Cite journal|author=Dauphas, N.|author2=Robert, F.|author3=Marty, B.|name-list-style=amp|date=December 2000|title=The Late Asteroidal and Cometary Bombardment of Earth as Recorded in Water Deuterium to Protium Ratio|journal=Icarus|volume=148|issue=2|pages=508–12|bibcode=2000Icar..148..508D |doi=10.1006/icar.2000.6489 |s2cid=85555707}}</ref>

Paleontology traces the evolutionary history of life back to over {{ma|3000|}}, possibly as far as {{ma|3800}}.<ref name="PiP">{{cite journal|last=Garwood|first=Russell J.|year=2012|title=Patterns In Palaeontology: The first 3 billion years of evolution|url=http://www.palaeontologyonline.com/articles/2012/patterns-in-palaeontology-the-first-3-billion-years-of-evolution/|url-status=live|journal=Palaeontology Online|volume=2|issue=11|pages=1–14|archive-url=https://web.archive.org/web/20150626104131/http://www.palaeontologyonline.com/articles/2012/patterns-in-palaeontology-the-first-3-billion-years-of-evolution/|archive-date=June 26, 2015|access-date=June 25, 2015}}</ref> The oldest clear evidence of life on Earth dates to {{ma|3000}}, although there have been reports, often disputed, of [[Biology:Fossil|fossil]] bacteria from {{ma|3400}} and of geochemical evidence for the presence of life {{ma|3800}}.<ref name="BrasierMcLoughlinEtAl2006FreshLook" /><ref>{{Cite journal|author=Schopf, J. |title=Fossil evidence of Archaean life |journal=Philos Trans R Soc Lond B Biol Sci |volume=361 |issue=1470 |pages=869–85 |date=2006 |pmid=16754604 |doi=10.1098/rstb.2006.1834 |pmc=1578735}}</ref> Some scientists have proposed that life on Earth was [[Biology:Panspermia|"seeded" from elsewhere]],<ref>{{Cite journal| author=Arrhenius, S. | title=The Propagation of Life in Space | date=1903
| journal=Die Umschau |volume=7| bibcode=1980qel..book...32A
| page=32 }} Reprinted in {{Cite book
| editor=Goldsmith, D. | title=The Quest for Extraterrestrial Life
| date=September 1982
| publisher=University Science Books | isbn=0-19-855704-3
}}</ref><ref>{{Cite journal
| author=Hoyle, F.
| author2=Wickramasinghe, C.
| name-list-style=amp | date=1979
| title=On the Nature of Interstellar Grains
| journal=Astrophysics and Space Science | volume=66 | issue=1
| pages=77–90
| doi=10.1007/BF00648361
| bibcode=1979Ap&SS..66...77H
| s2cid=115165958
}}</ref><ref>{{Cite journal
| last1 = Crick | first1 =  F.H. | last2 = Orgel | first2 = L.E.| title = Directed Panspermia
| journal = Icarus | volume = 19 | pages =  341–48 | date = 1973| doi = 10.1016/0019-1035(73)90110-3 | bibcode=1973Icar...19..341C
| issue = 3}}</ref> but most research concentrates on various explanations of how life could have [[Biology:Abiogenesis|arisen independently]] on Earth.<ref>{{Cite journal|author=Peretó, J. |title=Controversies on the origin of life |url=http://www.im.microbios.org/0801/0801023.pdf |journal=Int. Microbiol. |volume=8 |issue=1 |pages=23–31 |date=2005 |pmid=15906258 |access-date=October 7, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20150824074726/http://www.im.microbios.org/0801/0801023.pdf |archive-date=August 24, 2015 }}</ref>

For about 2,000 million years [[Biology:Microbial mat|microbial mat]]s, multi-layered colonies of different bacteria, were the dominant life on Earth.<ref name="KrumbeinBrehmEtAl2003BiofilmBiodictyonBiomatEtc">{{Cite book | contribution=Biofilm, Biodictyon, Biomat Microbialites, Oolites, Stromatolites, Geophysiology, Global Mechanism, Parahistology | author=Krumbein, W.E. | author2=Brehm, U. | author3=Gerdes, G. | author4=Gorbushina, A.A. | author5=Levit, G. | author6=Palinska, K.A. | name-list-style=amp | pages=1–28 | title=Fossil and Recent Biofilms: A Natural History of Life on Earth | editor=Krumbein, W.E. | editor2=Paterson, D.M. | editor3=Zavarzin, G.A. | date=2003 | publisher=Kluwer Academic | isbn=1-4020-1597-6 | url=http://134.106.242.33/krumbein/htdocs/Archive/397/Krumbein_397.pdf | access-date=July 9, 2008 | url-status=dead | archive-url=https://web.archive.org/web/20070106201614/http://134.106.242.33/krumbein/htdocs/Archive/397/Krumbein_397.pdf | archive-date=January 6, 2007 }}</ref> The evolution of [[Chemistry:Oxygen#Photosynthesis and respiration|oxygenic photosynthesis]] enabled them to play the major role in the [[Chemistry:Oxygen#Build-up in the atmosphere|oxygenation of the atmosphere]]<ref name="Hoehler" /> from about {{ma|2400}}. This change in the atmosphere increased their effectiveness as nurseries of evolution.<ref name="NisbetFowler1999ArchaeanMetabolicEvolution">{{Cite journal
 | title=Archaean metabolic evolution of microbial mats | author=Nisbet, E.G. | author2=Fowler, C.M.R. | name-list-style=amp
 | journal=Proceedings of the Royal Society B | date=December 7, 1999
| volume=266 | issue=1436 | page=2375 | doi=10.1098/rspb.1999.0934 | pmc=1690475
}}</ref> While [[Biology:Eukaryote|eukaryote]]s, cells with complex internal structures, may have been present earlier, their evolution speeded up when they acquired the ability to transform oxygen from a [[Chemistry:Poison|poison]] to a powerful source of [[Biology:Metabolism|metabolic]] energy. This innovation may have come from primitive eukaryotes capturing oxygen-powered bacteria as [[Biology:Endosymbiont|endosymbiont]]s and transforming them into [[Biology:Organelle|organelle]]s called [[Biology:Mitochondrion|mitochondria]].<ref name="PiP" /><ref>{{Cite journal|author=Gray M.W.|author2=Burger G.|author3=Lang B.F. |title=Mitochondrial evolution |journal=Science |volume=283 |issue=5407 |pages=1476–81 |date=March 1999 |pmid=10066161 |doi=10.1126/science.283.5407.1476|bibcode = 1999Sci...283.1476G |pmc=3428767 }}</ref> The earliest evidence of complex eukaryotes with organelles (such as mitochondria) dates from {{ma|1850}}.<ref name="HedgesBlairEtAl2004molecularTimescaleOfEukaryoteEvolution" />
[[File:20191108 Opabinia regalis.png| thumb | left| ''[[Biology:Opabinia|Opabinia]]'' sparked modern interest in the Cambrian explosion.]]
Multicellular life is composed only of eukaryotic cells, and the earliest evidence for it is the Francevillian Group Fossils from {{ma|2100}},<ref name="albani">{{Cite journal|author1=El Albani, Abderrazak |author2=Bengtson, Stefan |author3=Canfield, Donald E. |author4=Bekker, Andrey |author5=Macchiarelli, Reberto  |title=Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago |journal=Nature |volume=466 |issue=7302 |pages=100–04 |date=July 2010 |pmid=20596019 |doi=10.1038/nature09166 |bibcode = 2010Natur.466..100A|last6=Mazurier|first6=Arnaud|last7=Hammarlund|first7=Emma U.|last8=Boulvais|first8=Philippe|last9=Dupuy|first9=Jean-Jacques |s2cid=4331375 |display-authors=8}}</ref> although specialisation of cells for different functions first appears between {{ma|1430}} (a possible fungus) and {{ma|1200}} (a probable red alga). [[Biology:Sexual reproduction|Sexual reproduction]] may be a prerequisite for specialisation of cells, as an asexual multicellular organism might be at risk of being taken over by rogue cells that retain the ability to reproduce.<ref name="Butterfield2000Bangiomorpha">{{Cite journal | author=Butterfield, N.J. | date=September 2000 | title=''Bangiomorpha pubescens'' n. gen., n. sp.: implications for the evolution of sex, multicellularity, and the Mesoproterozoic/Neoproterozoic radiation of eukaryotes | journal=Paleobiology | volume=26 | issue=3 | pages=386–404 | doi=10.1666/0094-8373(2000)026<0386:BPNGNS>2.0.CO;2 | s2cid=36648568 | url=http://paleobiol.geoscienceworld.org/cgi/content/abstract/26/3/386 | access-date=September 2, 2008 | issn=0094-8373  | url-status=live | archive-url=https://web.archive.org/web/20070307035241/http://paleobiol.geoscienceworld.org/cgi/content/abstract/26/3/386 | archive-date=March 7, 2007 }}</ref><ref name="Butterfield2005ProterozoicFungi">{{Cite journal | author = Butterfield, N.J. | year = 2005 | title = Probable Proterozoic fungi | journal = Paleobiology | volume = 31 | issue = 1 | pages = 165–82 | doi = 10.1666/0094-8373(2005)031<0165:PPF>2.0.CO;2 | s2cid = 86332371 | url = http://paleobiol.geoscienceworld.org/cgi/content/abstract/31/1/165 | access-date = September 2, 2008 | issn = 0094-8373 | url-status=live | archive-url = https://web.archive.org/web/20090129211124/http://paleobiol.geoscienceworld.org/cgi/content/abstract/31/1/165 | archive-date = January 29, 2009 }}</ref>

The earliest known animals are [[Biology:Cnidaria|cnidaria]]ns from about {{ma|580}}, but these are so modern-looking that must be descendants of earlier animals.<ref>{{Cite journal
 |author          = Chen, J.-Y.
 |author2         = Oliveri, P.
 |author3         = Gao, F.
 |author4         = Dornbos, S.Q.
 |author5         = Li, C.-W.
 |author6         = Bottjer, D.J.
 |author7         = Davidson, E.H.
 |name-list-style = amp
 |title           = Precambrian Animal Life: Probable Developmental and Adult Cnidarian Forms from Southwest China
 |journal         = Developmental Biology
 |volume          = 248
 |issue           = 1
 |date            = August 2002
 |doi             = 10.1006/dbio.2002.0714
 |pages           = 182–96
 |url             = http://www.uwm.edu/~sdornbos/PDF's/Chen%20et%20al.%202002.pdf
 |access-date      = September 3, 2008
|pmid            = 12142030
 |url-status=dead
 |archive-url      = https://web.archive.org/web/20080911075353/http://www.uwm.edu/~sdornbos/PDF%27s/Chen%20et%20al.%202002.pdf
 |archive-date     = September 11, 2008
}}</ref> Early fossils of animals are rare because they had not developed mineralised, easily fossilized hard parts until about {{ma|548}}.<ref name="Bengtson2004">{{Cite journal
 |author=Bengtson, S.
 |editor=Lipps, J.H.
 |editor2=Waggoner, B.M.
 |title=Early Skeletal Fossils
 |date=2004
 |journal=The Paleontological Society Papers
 |volume=10 Neoproterozoic–Cambrian Biological Revolutions
 |pages=67–78
 |url=http://www.starregister.org/download/18.4e32c81078a8d9249800021554/Bengtson2004ESF.pdf
 |archive-url=https://web.archive.org/web/20090303221037/http://www.nrm.se/download/18.4e32c81078a8d9249800021554/Bengtson2004ESF.pdf
 |url-status=dead
 |archive-date=March 3, 2009
|access-date=July 18, 2008
|doi=10.1017/S1089332600002345
 }}</ref> The earliest modern-looking [[Biology:Bilateria|bilateria]]n animals appear in the Early [[Earth:Cambrian|Cambrian]], along with several "weird wonders" that bear little obvious resemblance to any modern animals. There is a long-running debate about whether this [[Earth:Cambrian explosion|Cambrian explosion]] was truly a very rapid period of evolutionary experimentation; alternative views are that modern-looking animals began evolving earlier but fossils of their precursors have not yet been found, or that the "weird wonders" are [[Biology:Stem group|evolutionary "aunts" and "cousins"]] of modern groups.<ref name="Marshall2006Explaining">{{Cite journal
| author=Marshall, C.R. | title=Explaining the Cambrian "Explosion" of Animals
| journal=Annu. Rev. Earth Planet. Sci. | date=2006 | volume=34 | pages=355–84
| doi=10.1146/annurev.earth.33.031504.103001
| bibcode=2006AREPS..34..355M
| s2cid=85623607
}}</ref> Vertebrates remained a minor group until the first jawed fish appeared in the Late [[Earth:Ordovician|Ordovician]].<ref>{{Cite journal
 |author=Conway Morris, S.
 |title=Once we were worms
 |date=August 2, 2003
|journal=New Scientist
 |volume=179
 |issue=2406
 |url=http://cas.bellarmine.edu/tietjen/Evolution/once_we_were_worms.htm
 |access-date=September 5, 2008
|page=34
 |url-status=dead
 |archive-url = https://web.archive.org/web/20080725103609/http://cas.bellarmine.edu/tietjen/Evolution/once_we_were_worms.htm
 |archive-date=July 25, 2008
}}</ref><ref>{{cite book
| author=Sansom I.J., Smith, M.M.
| author2=Smith, M.P.
| name-list-style=amp | date=2001
| contribution=The Ordovician radiation of vertebrates | pages=156–71
| editor=Ahlberg, P.E.  |title=Major Events in Early Vertebrate Evolution
| publisher=Taylor and Francis | isbn=0-415-23370-4
}}</ref>

[[File:Yanoconodon BW.jpg| thumb| At about {{convert|13|cm|in}} the Early Cretaceous ''[[Yanoconodon]]'' was longer than the average mammal of the time.<ref>{{Cite journal
| author=Luo, Z.
| author2=Chen, P.
| author3= Li, G.
| author4=Chen, M.
| name-list-style=amp | date=March 2007
| title=A new eutriconodont mammal and evolutionary development in early mammals
| journal=Nature | volume=446 | pages=288–93 | doi=10.1038/nature05627
| pmid=17361176
| issue=7133
|bibcode = 2007Natur.446..288L | s2cid=4329583
| url=http://doc.rero.ch/record/15542/files/PAL_E2954.pdf
}}</ref> ]]

The spread of animals and plants from water to land required organisms to solve several problems, including protection against drying out and supporting themselves against [[Physics:Gravity|gravity]].<ref name="Garwood">{{cite journal |author1=Russell Garwood  |author2=Gregory Edgecombe  |name-list-style=amp |year=2011 |title=''Early terrestrial animals, evolution and uncertainty'' |journal=Evolution: Education and Outreach |volume=4 |issue=3 |pages=489–501 |doi=10.1007/s12052-011-0357-y |doi-access=free }}</ref><ref name="Selden2001TerrestrializationOfAnimals">{{Cite book
| contribution=Terrestrialization of Animals | author=Selden, P.A. | pages=71–74
| title=Palaeobiology II: A Synthesis | editor=Briggs, D.E.G. | editor2=Crowther, P.R.  | date=2001
| publisher=Blackwell | isbn=0-632-05149-3
| url=https://books.google.com/books?id=AHsrhGOTRM4C&pg=PA71
}}</ref><ref name="KenrickCrane1997EvolutionOfLandPlants">{{Cite journal | author=Kenrick, P. | author2=Crane, P.R. | name-list-style=amp | title=The origin and early evolution of plants on land | journal=Nature | volume=389 | date=September 1997 | url=http://blog.richmond.edu/paleontology/files/2008/03/nature-evol-plants-kendrickcrane1997.pdf | doi=10.1038/37918 | page=33 | issue=6646 | bibcode=1997Natur.389...33K | s2cid=3866183 | url-status=dead | archive-url=https://web.archive.org/web/20101217123128/http://blog.richmond.edu/paleontology/files/2008/03/nature-evol-plants-kendrickcrane1997.pdf | archive-date=December 17, 2010 | access-date=November 11, 2010 }}</ref><ref>{{cite book |last=Laurin |first=M. |title=How Vertebrates Left the Water |publisher=University of California Press |location=Berkeley, California |date=2010 |isbn=978-0-520-26647-6 |author-link=Michel Laurin }}</ref> The earliest evidence of land plants and land invertebrates date back to about {{ma|476}} and {{ma|490}} respectively.<ref name="KenrickCrane1997EvolutionOfLandPlants" /><ref>{{Cite journal
 |author          = MacNaughton, R.B.
 |author2         = Cole, J.M.
 |author3         = Dalrymple, R.W.
 |author4         = Braddy, S.J.
 |author5         = Briggs, D.E.G.
 |author6         = Lukie, T.D.
 |name-list-style = amp
 |title           = First steps on land: Arthropod trackways in Cambrian-Ordovician eolian sandstone, southeastern Ontario, Canada
 |journal         = Geology
 |date            = May 2002
 |volume          = 30
 |issue           = 5
 |pages           = 391–94
 |doi             = 10.1130/0091-7613(2002)030<0391:FSOLAT>2.0.CO;2
 |bibcode         = 2002Geo....30..391M
 |issn            = 0091-7613
}}</ref> Those invertebrates, as indicated by their trace and body fossils, were shown to be arthropods known as euthycarcinoids.<ref>{{Cite journal
|author          =Collette, J.H.
|author2          =Gass, K.C.
|author3          =Hagadorn, J.W.
|name-list-style = amp
|title           = ''Protichnites eremita'' unshelled? Experimental model-based neoichnology and new evidence for a euthycarcinoid affinity for this ichnospecies
|journal         = Journal of Paleontology
|date            = May 2012
|volume          = 86
|issue           = 3
|pages           = 442–54
|doi             = 10.1666/11-056.1
|bibcode =2012JPal...86..442C
|s2cid =129234373
}}</ref> The lineage that produced land vertebrates evolved later but very rapidly between {{ma|370}} and {{ma|360}};<ref>{{Cite journal
| author=Gordon, M.S
| author2=Graham, J.B.
| author3=Wang, T.
| name-list-style=amp | title=Revisiting the Vertebrate Invasion of the Land
| journal=Physiological and Biochemical Zoology | volume=77 | issue=5
| date= September–October 2004 | doi=10.1086/425182 | pages=697–99
| s2cid=83750933
}}</ref> recent discoveries have overturned earlier ideas about the history and driving forces behind their evolution.<ref name="Clack2005GettingLegUp">{{Cite news
| author=Clack, J.A. | title=Getting a Leg Up on Land
| newspaper=Scientific American |date = November 2005| url=http://www.sciam.com/article.cfm?id=getting-a-leg-up-on-land | access-date=September 6, 2008
}}</ref> Land plants were so successful that their detritus caused an [[Earth:Ecological crisis|ecological crisis]] in the Late [[Earth:Devonian|Devonian]], until the evolution of fungi that could digest dead wood.<ref name="AlgeoScheckler1998errestrialMarineTeleconnectionsInDevonian"/>

[[File:House sparrow04.jpg|thumb|right|Birds are the only surviving dinosaurs.<ref name="padian2004" />]]
During the [[Earth:Permian|Permian]] period, [[Biology:Synapsid|synapsid]]s, including the ancestors of [[Biology:Mammal|mammal]]s, may have dominated land environments,<ref>{{Cite journal
| author2=O'Keefe, F.R.
| author3=Damiani, R.
| author4=Steyer, J.S.
| author5=Smith, R.M.H.
| author6=Larsson, H.C.E.
| author7=Sereno, P.C.
| author8=Ide, O
| author9=Maga, A.
| name-list-style=amp
| title=Permian tetrapods from the Sahara show climate-controlled endemism in Pangaea |date=April 2005
| journal=Nature | volume=434 | pages=886–89 | doi=10.1038/nature03393
| pmid=15829962
| issue=7035
|bibcode = 2005Natur.434..886S | s2cid=4416647
| url=http://doc.rero.ch/record/15308/files/PAL_E2607.pdf
}}</ref> but this ended with the [[Earth:Permian–Triassic extinction event|Permian–Triassic extinction event]] {{ma|251}}, which came very close to wiping out all complex life.<ref>{{Cite book
| author=Benton M.J. | date=2005 | title=When Life Nearly Died: The Greatest Mass Extinction of All Time
|publisher=Thames & Hudson | isbn=978-0-500-28573-2
}}</ref> The extinctions were apparently fairly sudden, at least among vertebrates.<ref>{{cite journal |last1=Ward |first1=P.D. |display-authors=4 |last2=Botha |first2=J. |last3=Buick |first3=R. |last4=Kock |first4=M.O. |last5=Erwin |first5=D.H. |last6=Garrisson |first6=G.H. |last7=Kirschvink |first7=J.L. |author7-link=Joseph Kirschvink |last8=Smith |first8=R. |date=2005 |title=Abrupt and gradual extinction among late Permian land vertebrates in the Karoo Basin, South Africa |journal=Science |volume=307 |pages=709–14 |doi=10.1126/science.1107068 |pmid=15661973 |issue=5710 |bibcode=2005Sci...307..709W |s2cid=46198018 |url=http://www.gps.caltech.edu/users/jkirschvink/pdfs/WardKarooScienceFinal.pdf |url-status=dead |archive-url=https://web.archive.org/web/20120813061414/http://www.gps.caltech.edu/users/jkirschvink/pdfs/WardKarooScienceFinal.pdf |archive-date=August 13, 2012 |access-date=October 25, 2017 }}</ref> During the slow recovery from this catastrophe a previously obscure group, [[Biology:Archosaur|archosaur]]s, became the most abundant and diverse terrestrial vertebrates. One archosaur group, the dinosaurs, were the dominant land vertebrates for the rest of the [[Earth:Mesozoic|Mesozoic]],<ref>{{Cite journal
| author=Benton, M.J.
| date=March 1983
| title=Dinosaur Success in the Triassic: a Noncompetitive Ecological Model
| journal=Quarterly Review of Biology
| volume=58
| issue=1
| pages=29–55
| doi=10.1086/413056
| s2cid=13846947
| url=http://palaeo.gly.bris.ac.uk/Benton/reprints/1983success.pdf
| access-date=September 8, 2008
| archive-url=https://web.archive.org/web/20080911075351/http://palaeo.gly.bris.ac.uk/Benton/reprints/1983success.pdf
| archive-date=September 11, 2008
| url-status=dead
}}</ref> and birds evolved from one group of dinosaurs.<ref name="padian2004">{{Cite book|last=Padian |first=Kevin |date=2004 |chapter=Basal Avialae |editor=Weishampel, David B. |editor2=Dodson, Peter |editor2-link=Peter Dodson |editor3=Osmólska, Halszka|title=The Dinosauria |edition=Second |location=Berkeley |publisher=University of California Press |pages=210–31 |isbn=0-520-24209-2}}</ref> During this time mammals' ancestors survived only as small, mainly nocturnal [[Biology:Insectivore|insectivore]]s, which may have accelerated the development of mammalian traits such as endothermy and hair.<ref name="RubenJones2000FurAndFeathers">{{Cite journal | author=Ruben, J.A. | author2=Jones, T.D. | name-list-style=amp | title=Selective Factors Associated with the Origin of Fur and Feathers | journal=American Zoologist | date=2000 | volume=40 | issue=4 | pages=585–96 | doi=10.1093/icb/40.4.585 | doi-access=free }}</ref> After the [[Earth:Cretaceous–Paleogene extinction event|Cretaceous–Paleogene extinction event]] {{ma|66}}<ref name="Renne2013">{{cite journal |last1=Renne |first1=Paul R. |last2=Deino |first2=Alan L. |last3=Hilgen |first3=Frederik J. |last4=Kuiper |first4=Klaudia F. |last5=Mark |first5=Darren F. |last6=Mitchell |first6=William S. |last7=Morgan |first7=Leah E. |last8=Mundil |first8=Roland |last9=Smit |first9=Jan |title=Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary |journal=Science |date=February 7, 2013 |volume=339 |issue=6120 |pages=684–87 |doi=10.1126/science.1230492 |pmid=23393261 |bibcode=2013Sci...339..684R|s2cid=6112274 |url=https://semanticscholar.org/paper/411afc826d678575392ec4d2dc7a6f25c389c7d0 }}</ref> killed off all the dinosaurs except the birds, mammals increased rapidly in size and diversity, and some took to the air and the sea.<ref>{{Cite journal
| author=Alroy J. |date=March 1999
| title=The fossil record of North American mammals: evidence for a Paleocene evolutionary radiation
| journal=Systematic Biology | volume=48 | issue=1 | pages=107–18 | pmid=12078635
| doi=10.1080/106351599260472
| doi-access=free }}</ref><ref>{{Cite journal
| author=Simmons, N.B.
| author2=Seymour, K.L.
| author3=Habersetzer, J.
| author4=Gunnell, G.F.
| name-list-style=amp |date=February 2008
| title=Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation
| journal=Nature | volume=451 | pages=818–21 | doi=10.1038/nature06549
| pmid=18270539
| issue=7180
|bibcode = 2008Natur.451..818S | url=http://deepblue.lib.umich.edu/bitstream/2027.42/62816/1/nature06549.pdf| hdl=2027.42/62816
| s2cid=4356708
| hdl-access=free
}}</ref><ref>{{Cite journal|author = J.G.M. [[Biography:Hans Thewissen|Thewissen]]|author2 = S.I. Madar|author3 = S.T. Hussain|name-list-style = amp|title = ''Ambulocetus natans'', an Eocene cetacean (Mammalia) from Pakistan|journal = Courier Forschungsinstitut Senckenberg|volume = 191|pages = 1–86|date = 1996
}}</ref>

<!--An ''[[Biology:Andrena|Andrena]]'' bee collects pollen among the stamens of a [[Biology:Rose|rose]]. The female carpel structure of the rose appears rough and globular to the left. The bee's stash of pollen is on its hind leg. Removed as surplus-->
Fossil evidence indicates that [[Biology:Flowering plant|flowering plant]]s appeared and rapidly diversified in the Early [[Earth:Cretaceous|Cretaceous]] between {{ma|130}} and {{ma|90}}.<ref name="CraneFriisPedersen2000OriginAndDiversificationOfAngiosperms">{{Cite book
| author1=Crane, P.R.
| author2=Friis, E.M.
| author3=Pedersen, K.R.
| name-list-style=amp
| chapter=The Origin and Early Diversification of Angiosperms | pages=233–50
| title=Shaking the Tree: Readings from Nature in the History of Life | editor=Gee, H.
| publisher=University of Chicago Press | date=2000 | isbn=0-226-28496-4
| chapter-url=https://books.google.com/books?id=ZJe_Dmdbm-QC&pg=PA233
}}</ref> Their rapid rise to dominance of terrestrial ecosystems is thought to have been propelled by [[Biology:Coevolution|coevolution]] with [[Biology:Pollination|pollinating]] insects.<ref name="Crepet2000">{{Cite journal
 |author      = Crepet, W.L.
 |date        = November 2000
 |title       = Progress in understanding angiosperm history, success, and relationships: Darwin's abominably "perplexing phenomenon"
 |journal     = Proceedings of the National Academy of Sciences
 |volume      = 97
 |issue       = 24
 |pages       = 12939–41
 |doi         = 10.1073/pnas.97.24.12939
 |pmid        = 11087846
 |pmc         = 34068
 |bibcode     = 2000PNAS...9712939C
|doi-access = free
 }}</ref> Social insects appeared around the same time and, although they account for only small parts of the insect "family tree", now form over 50% of the total mass of all insects.<ref name="WilsonHölldobler2005EusocialityOriginConsequences">{{Cite journal
 |author          = Wilson, E.O.
 |author2         = Hölldobler, B.
 |name-list-style = amp
 |title           = Eusociality: Origin and consequences
 |journal         = Proceedings of the National Academy of Sciences
 |date            = September 2005
 |volume          = 102
 |issue           = 38
 |pages           = 13367–71
 |doi             = 10.1073/pnas.0505858102
 |pmid            = 16157878
 |pmc             = 1224642
 |bibcode         = 2005PNAS..10213367W
|doi-access = free
 }}</ref>

Humans evolved from a lineage of upright-walking [[Biology:Ape|ape]]s whose earliest fossils date from over {{ma|6}}.<ref>{{Cite journal
| author=Brunet M., Guy
| author2= Pilbeam, F.
| author3=Mackaye, H.T.D.
| title=A new hominid from the Upper Miocene of Chad, Central Africa
| journal=Nature  | volume=418 | pages=145–51 |date=July 2002 | doi=10.1038/nature00879
| pmid=12110880
| issue=6894
| bibcode=2002Natur.418..145B
| s2cid=1316969
| url= http://doc.rero.ch/record/13388/files/PAL_E190.pdf
|display-authors=0
}}</ref> Although early members of this lineage had [[Biology:Common chimpanzee|chimp]]-sized brains, about 25% as big as modern humans', there are signs of a steady increase in brain size after about {{ma|3}}.<ref>{{Cite journal
| author=De Miguel, C.
| author2=Henneberg, M.
| name-list-style=amp
| title=Variation in hominid brain size: How much is due to method?
| journal=HOMO: Journal of Comparative Human Biology | issue=1 | date=2001
| doi=10.1078/0018-442X-00019 | pmid=11515396
| volume=52 | pages=3–58
}}</ref> There is a long-running debate about whether ''modern'' humans are descendants of a [[Biology:Recent African origin of modern humans|single small population in Africa]], which then migrated all over the world less than 200,000 years ago and replaced previous hominine species, or [[Biology:Multiregional origin of modern humans|arose worldwide at the same time]] as a result of interbreeding.<ref>{{Cite book|last=Leakey|first=Richard|author-link=Richard Leakey|title=The Origin of Humankind|publisher=Basic Books|location=New York|date=1994|series=Science Masters Series|pages=87–89|isbn=0-465-05313-0
}}</ref>
{{Clear}}

=== Mass extinctions ===
{{Annotated image/Extinction|caption=Apparent extinction intensity, i.e. the fraction of [[Biology:Genus|genera]] going extinct at any given time, as reconstructed from the fossil record (graph not meant to include recent epoch of [[Biology:Holocene extinction event|Holocene extinction event]])}}
Life on earth has suffered occasional mass extinctions at least since {{ma|542}}. Despite their disastrous effects, mass extinctions have sometimes accelerated the evolution of life on earth. When dominance of an [[Biology:Ecological niche|ecological niche]] passes from one group of organisms to another, this is rarely because the new dominant group outcompetes the old, but usually because an extinction event allows a new group, which may possess an advantageous trait, to outlive the old and move into its niche.<ref>{{Cite book| last=Benton | first =M.J. | title=Vertebrate Palaeontology | publisher=Blackwell | date=2004 | chapter=6. Reptiles of the Triassic | chapter-url=http://www.blackwellpublishing.com/book.asp?ref=0632056371 | access-date= November 17, 2008 | isbn=0-04-566002-6}}</ref><ref>{{Cite journal |last1=Sahney |first1=Sarda |last2=Benton |first2=Michael J. |last3=Ferry |first3=Paul A. |date=2010-08-23 |title=Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land |journal=Biology Letters |volume=6 |issue=4 |pages=544–547 |doi=10.1098/rsbl.2009.1024 |pmc=2936204 |pmid=20106856}}</ref><ref>{{Cite journal| last=Van Valkenburgh | first= B.| date=1999| title=Major patterns in the history of xarnivorous mammals | journal=Annual Review of Earth and Planetary Sciences| volume= 27| pages= 463–93 | doi= 10.1146/annurev.earth.27.1.463 |bibcode = 1999AREPS..27..463V | url= https://zenodo.org/record/890156}}</ref>

The fossil record appears to show that the rate of extinction is slowing down, with both the gaps between mass extinctions becoming longer and the average and background rates of extinction decreasing. However, it is not certain whether the actual rate of extinction has altered, since both of these observations could be explained in several ways:<ref name="MacLeod2001Extinction">{{cite web| date=January 6, 2001| first=Norman| last=MacLeod| title=Extinction!| url=http://www.firstscience.com/home/articles/earth/extinction-page-2-1_1258.html| access-date=September 11, 2008| url-status=dead| archive-url=https://web.archive.org/web/20080404150811/http://www.firstscience.com/home/articles/earth/extinction-page-2-1_1258.html| archive-date=April 4, 2008}}</ref>
* The oceans may have become more hospitable to life over the last 500&nbsp;million years and less vulnerable to mass extinctions: dissolved oxygen became more widespread and penetrated to greater depths; the development of life on land reduced the run-off of nutrients and hence the risk of [[Earth:Eutrophication|eutrophication]] and [[Earth:Anoxic event|anoxic event]]s; marine ecosystems became more diversified so that food chains were less likely to be disrupted.<ref>{{Cite journal| last=Martin| first= R.E.| date=1995| title=Cyclic and secular variation in microfossil biomineralization: clues to the biogeochemical evolution of Phanerozoic oceans| journal=Global and Planetary Change| volume =11| issue= 1| doi=10.1016/0921-8181(94)00011-2| page=1 |bibcode = 1995GPC....11....1M }}</ref><ref>{{Cite journal| last=Martin| first= R.E.| date=1996| title=Secular increase in nutrient levels through the Phanerozoic: Implications for productivity, biomass, and diversity of the marine biosphere| journal=PALAIOS| volume= 11| pages=209–19| doi=10.2307/3515230| issue=3| jstor=3515230
| bibcode=1996Palai..11..209M| s2cid= 67810793}}</ref>
* Reasonably complete [[Biology:Fossil|fossil]]s are very rare: most extinct organisms are represented only by partial fossils, and complete fossils are rarest in the oldest rocks. So paleontologists have mistakenly assigned parts of the same organism to different [[Biology:Genus|genera]], which were often defined solely to accommodate these finds&nbsp;– the story of ''[[Biology:Anomalocaris|Anomalocaris]]'' is an example of this.<ref name="WonderfulLifeP194To206">{{Cite book
| title=Wonderful Life: The Burgess Shale and the Nature of History | pages=194–206
| date=1990 | publisher=Hutchinson Radius | isbn=0-09-174271-4
}}</ref> The risk of this mistake is higher for older fossils because these are often unlike parts of any living organism. Many "superfluous" genera are represented by fragments that are not found again, and these "superfluous" genera are interpreted as becoming extinct very quickly.<ref name="MacLeod2001Extinction" />
{{Clear}}

{{Phanerozoic biodiversity}}
[[Biology:Biodiversity|Biodiversity]] in the fossil record, which is
:: "the number of distinct genera alive at any given time; that is, those whose first occurrence predates and whose last occurrence postdates that time"<ref name="RohdeMuller2005" />
shows a different trend: a fairly swift rise from {{ma|542|400}}, a slight decline from {{ma|400|200}}, in which the devastating [[Earth:Permian–Triassic extinction event|Permian–Triassic extinction event]] is an important factor, and a swift rise from {{ma|200}} to the present.<ref name="RohdeMuller2005">{{Cite journal
 |author          = Rohde, R.A.
 |author2         = Muller, R.A.
 |name-list-style = amp
 |title           = Cycles in fossil diversity
 |date            = March 2005
 |journal         = Nature
 |volume          = 434
 |pages           = 208–10
 |url             = http://muller.lbl.gov/papers/Rohde-Muller-Nature.pdf
 |access-date      = September 22, 2008
|doi             = 10.1038/nature03339
 |pmid            = 15758998
 |issue           = 7030
 |bibcode         = 2005Natur.434..208R
 |s2cid = 32520208
 |url-status=live
 |archive-url      = https://web.archive.org/web/20081003221929/http://muller.lbl.gov/papers/Rohde-Muller-Nature.pdf
 |archive-date     = October 3, 2008
}}</ref>

== History ==
{{Further|Earth:Timeline of paleontology}}
[[File:Cuvier elephant jaw.jpg|thumb|This illustration of an Indian elephant jaw and a mammoth jaw (top) is from Cuvier's 1796 paper on living and fossil elephants.]]

Although paleontology became established around 1800, earlier thinkers had noticed aspects of the [[Biology:Fossil|fossil]] record. The ancient Greek [[Philosophy:Philosophy#Ancient philosophy|philosopher]] [[Biography:Xenophanes|Xenophanes]] (570–480 BCE) concluded from fossil sea shells that some areas of land were once under water.<ref name="Rudwick">{{Cite book
|title=The Meaning of Fossils | pages=24, 39, 200–01
|publisher=The University of Chicago Press|date=1985|edition=2nd|isbn=0-226-73103-0
}}</ref> During the [[History:Middle Ages|Middle Ages]] the Persian naturalist [[Biography:Avicenna|Ibn Sina]], known as ''Avicenna'' in Europe, discussed fossils and proposed a theory of petrifying fluids on which [[Biography:Albert of Saxony (philosopher)|Albert of Saxony]] elaborated in the 14th century.<ref name="Rudwick" /> The Chinese naturalist [[Biography:Shen Kuo|Shen Kuo]] (1031–1095) proposed a theory of climate change based on the presence of petrified [[Biology:Bamboo|bamboo]] in regions that in his time were too dry for bamboo.<ref>{{Cite book
|title=''Science and Civilization in China: Volume 3, Mathematics and the Sciences of the Heavens and the Earth''
|page =614 | publisher=Caves Books Ltd|date=1986|isbn=0-253-34547-2
}}</ref>

In [[History:Early modern Europe|early modern Europe]], the systematic study of fossils emerged as an integral part of the changes in [[Philosophy:Natural philosophy|natural philosophy]] that occurred during the [[Philosophy:Age of Enlightenment|Age of Reason]]. In the Italian Renaissance, [[Biography:Leonardo da Vinci|Leonardo da Vinci]] made various significant contributions to the field as well as depicted numerous fossils. Leonardo's contributions are central to the history of paleontology because he established a line of continuity between the two main branches of paleontology{{snd}}ichnology and body fossil paleontology.<ref name=":0">Baucon, A. (2010). "Leonardo da Vinci, the founding father of ichnology". ''PALAIOS'' 25. Abstract available from the [http://www.tracemaker.com author's webpage]{{self-published inline|date=September 2020}}</ref><ref>Baucon A., Bordy E., Brustur T., Buatois L., Cunningham T., De C., Duffin C., Felletti F., Gaillard C., Hu B., Hu L., Jensen S., Knaust D., Lockley M., Lowe P., Mayor A., Mayoral E., Mikulas R., Muttoni G., Neto de Carvalho C., Pemberton S., Pollard J., Rindsberg A., Santos A., Seike K., Song H., Turner S., Uchman A., Wang Y., Yi-ming G., Zhang L., Zhang W. (2012). "A history of ideas in ichnology". In: Bromley R.G., Knaust D. ''Trace Fossils as Indicators of Sedimentary Environments. Developments in Sedimentology'', vol. 64. [http://www.tracemaker.com Tracemaker.com]{{self-published inline|date=September 2020}}</ref><ref>Baucon, A. (2010). "Da Vinci's ''Paleodictyon'': the fractal beauty of traces". ''Acta Geologica Polonica'', 60(1). Accessible from the [http://www.tracemaker.com author's homepage]{{self-published inline|date=September 2020}}</ref> He identified the following:<ref name=":0" />

# The biogenic nature of ichnofossils, i.e. ichnofossils were structures left by living organisms;
# The utility of ichnofossils as paleoenvironmental tools{{snd}}certain ichnofossils show the marine origin of rock strata;
# The importance of the neoichnological approach{{snd}}recent traces are a key to understanding ichnofossils;
# The independence and complementary evidence of ichnofossils and body fossils{{snd}}ichnofossils are distinct from body fossils, but can be integrated with body fossils to provide paleontological information

[[File:Anoplotherium_1812_Skeleton_Sketch.jpg|thumb|left|Georges Cuvier's 1812 sketch of a skeletal and muscle reconstruction of ''Anoplotherium commune''. This sketch was amongst the first instances of prehistoric animal reconstructions based on fossil remains.]]
At the end of the 18th century [[Biography:Georges Cuvier|Georges Cuvier]]'s work established comparative anatomy as a scientific discipline and, by proving that some fossil animals resembled no living ones, demonstrated that animals could become [[Biology:Extinction|extinct]], leading to the emergence of paleontology.<ref>{{Cite book|last=McGowan|first=Christopher|title=''The Dragon Seekers''|pages=[https://archive.org/details/dragonseekershow00mcgo_0/page/3 3–4]|publisher=Persus Publishing|date=2001|isbn=0-7382-0282-7|url=https://archive.org/details/dragonseekershow00mcgo_0/page/3}}</ref> The expanding knowledge of the fossil record also played an increasing role in the development of geology, particularly [[Earth:Stratigraphy|stratigraphy]].<ref name="Palmer2005EarthTime">{{Cite book|author=Palmer, D.|date=2005|title=Earth Time: Exploring the Deep Past from Victorian England to the Grand Canyon|publisher=Wiley|isbn=978-0470022214}}</ref> Cuvier proved that the different levels of deposits represented different time periods in the early 19th century. The surface-level deposits in the Americas contained later mammals like the megatheriid ground sloth ''[[Biology:Megatherium|Megatherium]]'' and the [[Biology:Mammutidae|mammutid]] proboscidean ''[[Biology:Mammut|Mammut]]'' (later known informally as a "mastodon"), which were some of the earliest-named fossil mammal genera with official taxonomic authorities. They today are known to date to the [[Earth:Neogene|Neogene]]-[[Earth:Quaternary|Quaternary]]. In deeper-level deposits in western Europe are early-aged mammals such as the palaeothere perissodactyl ''Palaeotherium'' and the [[Biology:Anoplotheriidae|anoplotheriid]] [[Biology:Artiodactyl|artiodactyl]] ''[[Biology:Anoplotherium|Anoplotherium]]'', both of which were described earliest after the former two genera, which today are known to date to the [[Earth:Paleogene|Paleogene]] period. Cuvier figured out that even older than the two levels of deposits with extinct large mammals is one that contained an extinct "crocodile-like" marine reptile, which eventually came to be known as the mosasaurid ''[[Biology:Mosasaurus|Mosasaurus]]'' of the [[Earth:Cretaceous|Cretaceous]] period.<ref>{{cite book|last=Wallace|first=David Rains|year=2004|title=Beasts of Eden: Walking Whales, Dawn Horses, and Other Enigmas of Mammal Evolution|chapter=Chapter 1: Pachyderms in the Catacombs|publisher=University of California Press|pages=1–13}}</ref>

[[File:Earliest-mention-of-the-word-palaeontology-in-January-1822-by-Blainville.jpg|thumb|right|First mention of the word ''palæontologie'', as coined in January 1822 by Henri Marie Ducrotay de Blainville in his ''Journal de physique'']]
The first half of the 19th century saw geological and paleontological activity become increasingly well organised with the growth of geologic societies and museums<ref>{{Cite book
|title=The Philosophy of Biology: An Episodic History | pages=128–30
|publisher=Cambridge University Press|date=2004|isbn=0-521-64371-6
}}</ref><ref>{{Cite book
|last=Bowler|first=Peter J.|author2=Iwan Rhys Morus|title=Making Modern Science | pages=168–69
|publisher=The University of Chicago Press|date=2005|isbn=0-226-06861-7
}}</ref> and an increasing number of professional geologists and fossil specialists. Interest increased for reasons that were not purely scientific, as geology and paleontology helped industrialists to find and exploit natural resources such as coal.<ref name="Rudwick" />
This contributed to a rapid increase in knowledge about the history of life on Earth and to progress in the definition of the [[Earth:Geologic time scale|geologic time scale]], largely based on fossil evidence. Although she was rarely recognised by the scientific community,<ref>{{Cite book|last=McGowan|first=Christopher|title=The Dragon Seekers|publisher=Persus Publishing|year=2001|isbn=978-0-7382-0282-2|location=Cambridge, MA|pages=14–21|language=English}}</ref> Mary Anning was a significant contributor to the field of palaeontology during this period; she uncovered multiple novel [[Earth:Mesozoic|Mesozoic]] reptile fossils and deducted that what were then known as bezoar stones are in fact fossilised faeces.<ref>{{Cite web|title=Mary Anning: the unsung hero of fossil discovery|url=https://www.nhm.ac.uk/discover/mary-anning-unsung-hero.html|access-date=2022-01-16|website=www.nhm.ac.uk|language=en}}</ref> In 1822 Henri Marie Ducrotay de Blainville, editor of ''Journal de Physique'', coined the word "palaeontology" to refer to the study of ancient living organisms through fossils.<ref>{{Cite book
|title=Worlds Before Adam: The Reconstruction of Geohistory in the Age of Reform |page=48
|publisher=The University of Chicago Press|date=2008|isbn=978-0-226-73128-5
}}</ref> As knowledge of life's history continued to improve, it became increasingly obvious that there had been some kind of successive order to the development of life. This encouraged early evolutionary theories on the [[Biology:Transmutation of species|transmutation of species]].<ref name="BucklandGould">{{Cite book|author=Buckland, W.|author2=Gould, S.J.|name-list-style=amp|title=Geology and Mineralogy Considered With Reference to Natural Theology (History of Paleontology)|date=1980|publisher=Ayer Company Publishing|isbn=978-0-405-12706-9}}</ref>
After [[Biography:Charles Darwin|Charles Darwin]] published ''Origin of Species'' in 1859, much of the focus of paleontology shifted to understanding [[Biology:Evolution|evolution]]ary paths, including [[Biology:Human evolution|human evolution]], and evolutionary theory.<ref name="BucklandGould"/>

[[File:Haikouichthys4.png| thumb| right | ''[[Biology:Haikouichthys|Haikouichthys]]'', from about {{ma|518}} in China, may be the earliest known fish<ref>{{citation | title = Head and backbone of the Early Cambrian vertebrate ''Haikouichthys'' | journal = Nature | first11 = H.-Q. | first1 = D.G. | last11 = Liu | last1 = Shu | first2 = S.C. | first10 = Y. | last2 = Morris | first3 = J. | last3 = Han | first4 = Z F. | last4 = Zhang | last10 = Li | first5 = K. | last5 = Yasui | first6 = P. | last6 = Janvier | first7 = L. | last7 = Chen | first8 = X.L. | last8 = Zhang | first9 = J.N. | last9 = Liu | volume = 421 | issue = 6922 | doi = 10.1038/nature01264 | bibcode = 2003Natur.421..526S | pmid = 12556891 | url = https://www.researchgate.net/publication/10926399 | pages = 526–29 | date = 2003 | s2cid = 4401274 | url-status=live | archive-url = https://web.archive.org/web/20151124194721/http://www.researchgate.net/publication/10926399_Head_and_backbone_of_the_Early_Cambrian_vertebrate_Haikouichthys | archive-date = November 24, 2015 }}</ref>]]
The last half of the 19th century saw a tremendous expansion in paleontological activity, especially in North America.<ref>{{Cite book
|last=Everhart|first=Michael J.
|title=''Oceans of Kansas: A Natural History of the Western Interior Sea'' | page=17
|publisher=Indiana University Press|date=2005|isbn=0-253-34547-2
}}</ref> The trend continued in the 20th century with additional regions of the Earth being opened to systematic fossil collection. Fossils found in China near the end of the 20th century have been particularly important as they have provided new information about the earliest evolution of animals, early fish, dinosaurs and the evolution of birds.<ref>{{Cite book
| editor=Gee, H. | title=Rise of the Dragon: Readings from Nature on the Chinese Fossil Record | date=2001 | isbn=0-226-28491-3 | page=276
| url=https://books.google.com/books?id=6WYZQwmyWy0C
| publisher=University of Chicago Press

Increasing awareness of [[Biography:Gregor Mendel|Gregor Mendel]]'s pioneering work in [[Biology:Genetics|genetics]] led first to the development of [[Biology:Population genetics|population genetics]] and then in the mid-20th century to the [[Biology:Modern synthesis (20th century)|modern evolutionary synthesis]], which explains [[Biology:Evolution|evolution]] as the outcome of events such as [[Biology:Mutation|mutation]]s and [[Biology:Horizontal gene transfer|horizontal gene transfer]], which provide [[Biology:Genetic variation|genetic variation]], with [[Biology:Genetic drift|genetic drift]] and [[Biology:Natural selection|natural selection]] driving changes in this variation over time.<ref name="Bowler–Idea" /> Within the next few years the role and operation of [[Biology:DNA|DNA]] in genetic inheritance were discovered, leading to what is now known as the [[Biology:Central dogma of molecular biology|"Central Dogma" of molecular biology]].<ref>{{cite web
 |author=Crick, F.H.C.
 |title = On degenerate templates and the adaptor hypothesis
 |year = 1955
 |url = http://genome.wellcome.ac.uk/assets/wtx030893.pdf
 |access-date = October 4, 2008
|url-status=dead
 |archive-url = https://web.archive.org/web/20081001223217/http://genome.wellcome.ac.uk/assets/wtx030893.pdf
 |archive-date = October 1, 2008
}}</ref> In the 1960s [[Biology:Molecular phylogenetics|molecular phylogenetics]], the investigation of evolutionary "family trees" by techniques derived from [[Biology:Biochemistry|biochemistry]], began to make an impact, particularly when it was proposed that the human lineage had diverged from [[Biology:Ape|ape]]s much more recently than was generally thought at the time.<ref>{{Cite journal
| author1 = Sarich, V.M.
| author2 = Wilson, A.C.
| name-list-style=amp | title=Immunological time scale for hominid evolution
| journal=Science | volume=158 | issue=3805|date=December 1967 | pages=1200–03 | doi=10.1126/science.158.3805.1200
| pmid=4964406
|bibcode = 1967Sci...158.1200S | s2cid = 7349579
}}</ref> Although this early study compared [[Biology:Protein|protein]]s from apes and humans, most molecular phylogenetics research is now based on comparisons of [[Biology:RNA|RNA]] and [[Biology:DNA|DNA]].<ref>{{Cite book
| author1 = Page, R.D.M.
| author2 = Holmes, E.C.
| name-list-style=amp |title = Molecular Evolution: A Phylogenetic Approach| page=2
| year = 1998 |isbn = 0-86542-889-1
| publisher=Blackwell Science
| location=Oxford
}}</ref>

== Paleontology in the vernacular press ==
Books catered to the general public on paleontology include:

* The Last Days of the Dinosaurs: An Asteroid Extinction, and the Beginning of our World<ref>{{Cite book |last=Black |first=Riley |title=The Last Days of the Dinosaurs: An Asteroid, Extinction, and the Beginning of Our World |publisher=St. Martin's Press |year=2022 |isbn=978-1250271044 |edition=1st |location=United States |language=English}}</ref> written by Riley Black
* The Rise and Reign of the Mammals: A New History, from the Shadow of the Dinosaurs to Us<ref>{{Cite book |last=Brusatte |first=Steve |title=The Rise and Reign of the Mammals: A New History, from the Shadow of the Dinosaurs to Us |publisher=Mariner Books |year=2022 |isbn=978-0062951519 |edition=1st |location=United States |language=English}}</ref> written by Steve Brusatte
* Otherlands: A Journey Through Earth's Extinct Worlds<ref>{{Cite book |last=Halliday |first=Thomas |title=Otherlands: A Journey Through Earth's Extinct Worlds |publisher=Random House |year=2022 |isbn=978-0593132883 |edition=1st |location=United States |language=English}}</ref> written by Thomas Halliday

== See also ==
{{div col |colwidth = 30em }}
* {{annotated link|Earth:Biostratigraphy}}
* {{annotated link|Earth:European land mammal age}}
* {{annotated link|Biology:Fossil collecting}}
* {{annotated link|Biology:List of fossil sites}} (''with link directory'')
* List of notable fossils
* List of paleontologists
* [[Biology:List of transitional fossils|List of transitional fossils]]
* {{annotated link|Biology:Paleoanthropology}}
* {{annotated link|Biology:Paleobotany}}
* {{annotated link|Biology:Paleogenetics}}
* {{annotated link|Biology:Paleontographer}}
* {{annotated link|Biology:Paleophycology}}
* {{annotated link|Physics:Radiometric dating}}
* {{annotated link|Biology:Taxonomy of commonly fossilised invertebrates}}
* {{annotated link|Treatise on Invertebrate Paleontology}}
* ''Une Femme ou Deux'' - French screwball comedy romance film starring Gérard Depardieu as a paleontologist.

{{div col end}}

== Notes  ==
{{notelist}}

== References ==
{{Reflist}}

== External links ==
* [http://paleobiology.si.edu/ Smithsonian's Paleobiology website]
* [http://www.ucmp.berkeley.edu/ University of California Museum of Paleontology]
* [http://www.paleosoc.org The Paleontological Society]
* [http://www.palass.org The Palaeontological Association]
* [http://vertpaleo.org The Society of Vertebrate Paleontology]
* [http://www.paleoportal.org The Paleontology Portal]
* [http://lhldigital.lindahall.org/cdm/search/collection/earththeory "Geology, Paleontology & Theories of the Earth"] – a collection of more than 100 digitised landmark and early books on Earth sciences at the Linda Hall Library

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[[Category:Paleontology| ]]
[[Category:Earth sciences]]
[[Category:Evolutionary biology]]
[[Category:Fossils|*]]
[[Category:Historical geology]]

{{Sourceattribution|Paleontology}}