View source for Earth:Boring Billion

{{Short description|Earth history, 1.8 to 0.8 billion years ago}}
{{Life timeline}}
The '''Boring Billion''', otherwise known as the '''Mid Proterozoic''' and '''Earth's Middle Ages''', is the time period between 1.8 and 0.8 billion years ago (Ga) spanning the middle [[Earth:Proterozoic|Proterozoic]] [[Earth:Eon (geology)|eon]], characterized by more or less tectonic stability, [[Earth:Climate|climatic]] stasis, and slow [[Biology:Evolution|biological evolution]]. It is bordered by two different oxygenation and glacial events, but the Boring Billion itself had very low oxygen levels and no evidence of glaciation.

The oceans may have been oxygen- and nutrient-poor and sulfidic ([[Earth:Euxinia|euxinia]]), populated by mainly [[Biology:Anoxygenic photosynthesis|anoxygenic]] [[Biology:Purple bacteria|purple bacteria]], a type of chlorophyll-based photosynthetic bacteria which uses [[Chemistry:Hydrogen sulfide|hydrogen sulfide]] (H<sub>2</sub>S) instead of [[Chemistry:Water|water]] and produces [[Chemistry:Sulfur|sulfur]] instead of [[Chemistry:Oxygen|oxygen]]. This is known as a [[Earth:Canfield ocean|Canfield ocean]]. Such composition may have caused the oceans to be black- and milky-turquoise instead of blue or green.  (By contrast, during the much earlier Purple Earth phase the photosynthesis was [[Chemistry:Retinal|retinal]]-based.)

Despite such adverse conditions, [[Biology:Eukaryote|eukaryote]]s may have evolved around the beginning of the Boring Billion, and adopted several novel adaptations, such as various [[Biology:Organelle|organelle]]s, multicellularity, and possibly [[Biology:Evolution of sexual reproduction|sexual reproduction]], and diversified into [[Biology:Plant|plant]]s, [[Biology:Animal|animal]]s, and [[Biology:Fungi|fungi]] at the end of this time interval.<ref name=Mukherjee2018/> Such advances may have been important precursors to the evolution of large, complex life later in the [[Earth:Ediacaran|Ediacaran]] and [[Earth:Phanerozoic|Phanerozoic]]. Nonetheless, prokaryotic cyanobacteria were the dominant lifeforms during this time, and likely supported an energy-poor food-web with a small number of [[Biology:Protist|protist]]s at the [[Biology:Apex predator|apex level]]. The land was likely inhabited by prokaryotic cyanobacteria and eukaryotic proto-[[Biology:Lichen|lichen]]s, the latter more successful here probably due to the greater availability of nutrients than in offshore ocean waters.

==Description==
In 1995, geologists Roger Buick, Davis Des Marais, and Andrew Knoll reviewed the apparent lack of major biological, geological, and climatic events during the [[Earth:Mesoproterozoic|Mesoproterozoic]] [[Physics:Era|era]] 1.6 to 1 billion years ago (Ga), and, thus, described it as "the dullest time in Earth's history".<ref name=Buick1995>{{Cite journal|title = Stable isotopic compositions of carbonates from the Mesoproterozoic Bangemall group, northwestern Australia|journal = Chemical Geology|year=1995|pages = 153–171|volume = 123|issue = 1–4|doi = 10.1016/0009-2541(95)00049-R|pmid = 11540130|first1 = R.|last1 = Buick|first2 = D. J.|last2 = Des Marais|first3 = A. H.|last3 = Knoll|bibcode = 1995ChGeo.123..153B}}</ref> The term "Boring Billion" was coined by paleontologist [[Biography:Martin Brasier|Martin Brasier]] to refer to the time between about 2 and 1 Ga, which was characterized by geochemical stasis and glacial stagnation.<ref>{{cite book|first=M.|last=Brasier|year=2012|title=Secret Chambers: The Inside Story of Cells and Complex Life|publisher=Oxford University Press|page=211|isbn=978-0-19-964400-1}}</ref> In 2013, geochemist Grant Young used the term "Barren Billion" to refer to a period of apparent glacial stagnation and lack of [[Physics:Isotopes of carbon#Paleoclimate|carbon isotope excursion]]s from 1.8 to 0.8 Ga.<ref name=:4/> In 2014, geologists Peter Cawood and Chris Hawkesworth called the time between 1.7 and 0.75 Ga "Earth's Middle Ages" due to a lack of evidence of tectonic movement.<ref name=":1"/>

The Boring Billion is now largely cited as spanning about 1.8 to 0.8 Ga, contained within the [[Earth:Proterozoic|Proterozoic]] [[Earth:Eon (geology)|eon]], mainly the Mesoproterozoic. The Boring Billion is characterized by geological, climatic, and by-and-large evolutionary stasis, with low nutrient abundance.<ref name=":0"/><ref name=":4"/><ref name=Holland2006/><ref name=Peng2019/>

In the time leading up to the Boring Billion, Earth experienced the [[Earth:Great Oxygenation Event|Great Oxygenation Event]] due to the evolution of oxygenic photosynthetic [[Biology:Cyanobacteria|cyanobacteria]], and the resultant [[Earth:Huronian glaciation|Huronian glaciation]] ([[Earth:Snowball Earth|Snowball Earth]]), formation of the UV-blocking [[Physics:Ozone layer|ozone layer]], and oxidation of several metals.<ref name=":10">{{Cite book| year = 2011| last1 = Lenton| first1 = T.| last2 = Watson| first2 = A.| pages = 242–261| doi = 10.1093/acprof:oso/9780199587049.003.0013|chapter=The not-so-boring billion|title = Revolutions that made the Earth|isbn = 978-0-19-958704-9}}</ref> Oxygen levels during the Boring Billion are thought to have been markedly lower than during the Great Oxidation Event, perhaps 0.1% to 10% of modern levels.<ref name=":10" /><ref>{{Cite journal |last1=Planavsky |first1=Noah J. |last2=Cole |first2=Devon B. |last3=Isson |first3=Terry T. |last4=Reinhard |first4=Christopher T. |last5=Crockford |first5=Peter W. |last6=Sheldon |first6=Nathan D. |last7=Lyons |first7=Timothy W. |date=2018-08-09 |title=A case for low atmospheric oxygen levels during Earth's middle history |url=https://doi.org/10.1042/ETLS20170161 |journal=Emerging Topics in Life Sciences |volume=2 |issue=2 |pages=149–159 |doi=10.1042/etls20170161 |pmid=32412619 |s2cid=210099422 |issn=2397-8554}}</ref> It was ended by the breakup of the supercontinent [[Earth:Rodinia|Rodinia]] during the [[Earth:Tonian|Tonian]] (1000–720 Ma) period, a second oxygenation event, and another Snowball Earth in the [[Earth:Cryogenian|Cryogenian]] period.<ref name=":1">{{Cite journal|title = Earth's middle age|journal = Geology|date = 2014-06-01|issn = 0091-7613|pages = 503–506|volume = 42|issue = 6|doi = 10.1130/G35402.1|language = en|first1 = Peter A.|last1 = Cawood|first2 = Chris J.|last2 = Hawkesworth|bibcode = 2014Geo....42..503C|doi-access = free|hdl = 10023/4569|hdl-access = free}}</ref><ref name=Brooke2014/>

== Tectonic stasis ==
{{Multiple image|direction=vertical|image1=Paleoglobe NO 1590 mya-vector-colors.svg|image2=|footer=Reconstruction of [[Earth:Columbia (supercontinent)|Columbia]] (1.6 Gya)}}
The evolution of Earth's [[Biology:Biosphere|biosphere]], atmosphere, and [[Earth:Hydrosphere|hydrosphere]] has long been linked to the [[Supercontinent cycle|supercontinent cycle]], where the continents aggregate and then drift apart. The Boring Billion saw the evolution of two supercontinents: [[Earth:Columbia (supercontinent)|Columbia]] (or Nuna) and [[Earth:Rodinia|Rodinia]].<ref name=":0"/><ref name=Evans2013/>

The supercontinent Columbia formed between 2.0 and 1.7&nbsp;Ga and remained intact until at least 1.3&nbsp;Ga. Geological and [[Earth:Paleomagnetism|paleomagnetic]] evidence suggest that Columbia underwent only minor changes to form the supercontinent Rodinia from 1.1 to 0.9&nbsp;Ga. [[Earth:Palaeogeography|Paleogeographic]] reconstructions suggest that the supercontinent assemblage was located in [[Astronomy:Equator|equator]]ial and [[Earth:Temperate climate|temperate]] climate zones, and there is little or no evidence for continental fragments in polar regions.<ref name=Evans2013>{{Cite journal|title = Reconstructing pre-Pangean supercontinents|year=2013|journal = Geological Society of America Bulletin|pages = 1735–1751|volume = 125|issue = 11–12|doi = 10.1130/b30950.1|first = D. A. D.|last = Evans|bibcode = 2013GSAB..125.1735E}}</ref>

Due to the lack of evidence of sediment build-up (on passive margins) which would occur as a result of [[Earth:Rift|rift]]ing,<ref>{{Cite journal|title = Passive margins through earth history|journal = Earth-Science Reviews|date = 2008-12-01|pages = 1–26|volume = 91|issue = 1–4|doi = 10.1016/j.earscirev.2008.08.001|first = Dwight C.|last = Bradley|bibcode = 2008ESRv...91....1B|url = https://zenodo.org/record/1258907}}</ref> the supercontinent probably did not break up, and rather was simply an assemblage of juxtaposed proto-continents and [[Earth:Craton|craton]]s. There is no evidence of rifting until the formation of Rodinia, 1.25 Ga in North Laurentia, and 1 Ga in East [[Earth:Baltica|Baltica]] and South Siberia.<ref name=":0"/><ref name=":1" /> Breakup did not occur until 0.75 Ga, marking the end of the Boring Billion.<ref name=":1" /> This tectonic stasis may have been related in ocean and atmospheric chemistry.<ref name=":0">{{Cite journal|title = The boring billion? – Lid tectonics, continental growth and environmental change associated with the Columbia supercontinent|journal = Geoscience Frontiers|year=2013 |df=dmy-all |pages = 681–691|volume = 4|series = Thematic Section: Antarctica – A window to the far off land|issue = 6|doi = 10.1016/j.gsf.2013.05.004|first = N. M. W.|last = Roberts| bibcode=2013GeoFr...4..681R |doi-access = free}}</ref><ref name=Holland2006>{{Cite journal|title = The oxygenation of the atmosphere and oceans|journal = Philosophical Transactions of the Royal Society of London B: Biological Sciences|date = 2006-06-29|issn = 0962-8436|pmc = 1578726|pmid = 16754606|pages = 903–915|volume = 361|issue = 1470|doi = 10.1098/rstb.2006.1838|language = en|first = Heinrich D.|last = Holland}}</ref><ref name=":1" />

It is possible the [[Earth:Asthenosphere|asthenosphere]]—the molten layer of Earth's [[Earth:Mantle (geology)|mantle]] that tectonic plates essentially float and move around upon—was too hot to sustain modern plate tectonics at this time. Instead of vigorous plate recycling at [[Earth:Subduction|subduction zones]], plates were linked together for billions of years until the mantle cooled off sufficiently. The onset of this component of plate tectonics may have been aided by the cooling and thickening of the [[Earth:Crust (geology)|crust]] that, once initiated, made plate subduction anomalously strong, occurring at the end of the Boring Billion.<ref name=":1" />

Nonetheless, major [[Biology:Magma|magma]]tic events still occurred, such as the formation (via magma plume) of the {{cvt|220,000|km2|mi2|adj=on}} central Australian Musgrave Province from 1.22 to 1.12 Ga,<ref>{{cite journal|first1=W.|last1=Gorczyk|first2=H.|last2=Smithies|first3=F.|last3=Korhonen|first4=H.|last4=Howard|first5=R. Q.|last5=de Gromard|year=2015|title=Ultra-hot Mesoproterozoic evolution of intracontinental central Australia|journal=Geoscience Frontiers|volume=6|issue=1|pages=23–37|doi=10.1016/j.gsf.2014.03.001|bibcode=2015GeoFr...6...23G |doi-access=free}}</ref> and the {{cvt|2,700,000|km2|mi2}} Canadian [[Earth:Mackenzie Large Igneous Province|Mackenzie Large Igneous Province]] 1.27 Ga.<ref>{{cite journal|first1=S. E.|last1=Bryan|first2=L.|last2=Ferrari|year=2013|title=Large igneous provinces and silicic large igneous provinces: Progress in our understanding over the last 25 years|journal=GSA Bulletin|volume=125|issue=7–8|page=1055<!--only citing this page-->|doi=10.1130/B30820.1|bibcode=2013GSAB..125.1053B|doi-access=free}}</ref> Plate tectonics were still active enough to build mountains, with several orogenies, including the Grenville orogeny,<ref name="one">{{Cite book |last1=Tollo |first1=R. P. |first2=L.|last2=Corriveau |first3=J.|last3=McLelland |first4=M. J.|last4=Bartholomew  |year=2004 |chapter=Proterozoic tectonic evolution of the Grenville orogen in North America: An introduction |editor1-last=Tollo |editor1-first=R. P. |editor2-first=L. |editor2-last=Corriveau |editor3-first=J. |editor3-last=McLelland |editor4-first=M. J. |editor4-last=Bartholomew |title=Proterozoic tectonic evolution of the Grenville orogen in North America |series=Geological Society of America Memoir |volume=197 |pages=1–18 |chapter-url=https://books.google.com/books?id=uT4HISRCon8C&pg=PA1  |isbn=978-0-8137-1197-3 }}</ref> occurring at the time.

== Climatic stability ==
[[File:Mesoproterozoic temperature.jpg|thumb|300px|Graph showing average temperatures during the Mesoproterozoic. Blue line uses CO<sub>2</sub> concentration 5 times modern day, red line 10 times, and red dot shows average temperature range at the tropics]]
There is little evidence of significant climatic variability during this time period.<ref name=":4">{{Cite journal|title = Precambrian supercontinents, glaciations, atmospheric oxygenation, metazoan evolution and an impact that may have changed the second half of Earth history|journal = Geoscience Frontiers|year=2013|pages = 247–261|volume = 4|issue = 3|doi = 10.1016/j.gsf.2012.07.003|first = Grant M.|last = Young| bibcode=2013GeoFr...4..247Y |doi-access = free}}</ref><ref>{{Cite journal |title = A billion years of environmental stability and the emergence of eukaryotes: New data from northern Australia |last = Brasier |first = M.D. |year= 1998 |journal = Geology|doi =10.1130/0091-7613(1998)026<0555:ABYOES>2.3.CO;2 |pmid = 11541449 |volume=26 |issue = 6|pages = 555–558 |bibcode = 1998Geo....26..555B }}</ref>  Climate was likely not primarily dictated by solar luminosity because the [[Astronomy:Sun|Sun]] was 5–18% less luminous than it is today, but there is no evidence that Earth's climate was significantly cooler.<ref name="Fiorella2017">{{cite journal|first1=R.|last1=Fiorella|first2=N.|last2=Sheldon|year=2017|title=Equable end Mesoproterozoic climate in the absence of high CO2|journal=Geology|volume=45|issue=3|pages=231–234|url=https://www.researchgate.net/publication/311885954|doi=10.1130/G38682.1|bibcode=2017Geo....45..231F}}</ref><ref name=Veizer2005/> In fact, the Boring Billion seems to lack any evidence of prolonged glaciations, which can be observed at regular periodicity in other parts of Earth's geologic history.<ref name=Veizer2005/> High CO<sub>2</sub> could not have been a main driver for warming because levels would have needed to be 30 to 100 times greater than pre-[[History:Industrial Revolution|industrial]] levels<ref name=Fiorella2017/> and produced substantial [[Biology:Ocean acidification|ocean acidification]]<ref name=Veizer2005/> to prevent ice formation, which also did not occur. Mesoproterozoic CO<sub>2</sub> levels may have been comparable to those of the [[Earth:Phanerozoic|Phanerozoic]] eon, perhaps 7 to 10 times higher than modern levels.<ref name=Kah2007>{{cite journal|first1=L. C.|last1=Kah|first2=R.|last2=Riding|s2cid=129389459|year=2007|title=Mesoproterozoic carbon dioxide levels inferred from calcified cyanobacteria|journal=Geology|volume=35|issue=9|pages=799–802|doi=10.1130/G23680A.1|bibcode=2007Geo....35..799K}}</ref> The first record of ice from this time period was reported in 2020 from the 1 Ga Scottish Diabaig Formation in the Torridon Group, where [[Earth:Dropstone|dropstone]] formations were likely formed by debris from ice rafting; the area, then situated between 35–50°S, was a (possibly upland) lake which is thought to have frozen over in the winter and melted in the summer, rafting occurring in the spring melt.<ref>{{cite journal|first1=A.|last1=Hartley|first2=B.|last2=Kurjanski|first3=J.|last3=Pugsley|first4=J.|last4=Armstrong|year=2020|title=Ice-rafting in lakes in the early Neoproterozoic: dropstones in the Diabaig Formation, Torridon Group, NW Scotland|journal=Scottish Journal of Geology|volume=56|issue=1 |pages=47–53|doi=10.1144/sjg2019-017|bibcode=2020ScJG...56...47H |hdl=2164/15493|s2cid=214436923|hdl-access=free}}</ref>

A higher abundance of other greenhouse gases, namely methane produced by prokaryotes, may have compensated for the low CO<sub>2</sub> levels; a largely ice-free world achieved by an [[Earth:Atmospheric methane|atmospheric methane]] concentration of 140 [[Parts per million|parts per million]] (ppm).<ref name=Kah2007/><ref name=Fiorella2017/> Methanogenic prokaryotes could not have produced so much methane, implying some other greenhouse gas, probably [[Chemistry:Nitrous oxide|nitrous oxide]], was elevated, perhaps to 3 ppm (10 times today's levels). Based on presumed greenhouse gas concentrations, equatorial temperatures during the Mesoproterozoic may have been about {{cvt|295–300|K|C F}}, in the tropics {{cvt|290|K|C F}}, at 60° {{cvt|265–280|K|C F}}, and the poles {{cvt|250–275|K|C F}};<ref>{{cite journal|first1=M. T.|last1=Hren|first2=N. D.|last2=Sheldon|year=2020|title=Terrestrial microbialites provide constraints on the mesoproterozoic atmosphere|journal=The Depositional Record|volume=6|issue=1 |pages=4–20|doi=10.1002/dep2.79|bibcode=2020DepRe...6....4H |doi-access=free|hdl=2027.42/154283|hdl-access=free}}</ref> and the global average temperature about {{cvt|19|C|F}}, which is 4&nbsp;°C (7.2&nbsp;°F) warmer than today. Temperatures at the poles dropped below freezing in winter, allowing for temporary sea ice formation and snowfall, but there were likely no permanent ice sheets.<ref name=Peng2019>{{cite journal|first1=L.|last1=Peng|first2=L.|last2=Yonggang|first3=H.|last3=Yongyun|first4=Y.|last4=Yun|first5=S. A.|last5=Pisarevsky|year=2019|title=Warm Climate in the "Boring Billion" Era|journal=Acta Geologica Sinica|volume=93|issue=S3 |pages=40–43|doi=10.1111/1755-6724.14239|bibcode=2019AcGlS..93R..40L |doi-access=free}}</ref>

It has also been proposed that, because the intensity of [[Astronomy:Cosmic ray|cosmic ray]]s has been shown to be positively correlated to cloud cover, and cloud cover reflects light into space and reduces global temperatures, lower rates of bombardment during this time due to reduced star formation in the galaxy caused less cloud cover and prevented glaciation events, maintaining a warm climate.<ref name=Veizer2005>{{Cite journal|title = Celestial Climate Driver: A Perspective from Four Billion Years of the Carbon Cycle|url = https://journals.lib.unb.ca/index.php/GC/article/view/2691|journal = Geoscience Canada|year=2005 |df=dmy-all |issn = 1911-4850|volume = 32|issue = 1|first = J.|last = Veizer}}</ref><ref>{{Cite journal| last = Shaviv| first = Nir J.| year=2003 |df=dmy-all| title = The spiral structure of the Milky Way, cosmic rays, and ice age epochs on Earth| journal = New Astronomy| volume = 8| issue = 1| pages = 39–77| doi = 10.1016/S1384-1076(02)00193-8| arxiv = astro-ph/0209252| bibcode = 2003NewA....8...39S| s2cid = 879406}}</ref> Also, some combination of weathering intensity which would have reduced CO<sub>2</sub> levels by oxidation of exposed metals, cooling of the [[Earth:Mantle (geology)|mantle]] and reduced geothermal heat and volcanism, and increasing solar intensity and solar heat may have reached an equilibrium, barring ice formation.<ref name=":4" />

Conversely, glacial movements over a billion years ago may not have left many remnants today, and an apparent lack of evidence could be due to the incompleteness of the fossil record rather than absence. Further, the low oxygen and solar intensity levels may have prevented the formation of the [[Physics:Ozone layer|ozone layer]], preventing [[Chemistry:Greenhouse gas|greenhouse gas]]ses from being trapped in the atmosphere and heating the Earth via the [[Earth:Greenhouse effect|greenhouse effect]], which would have caused glaciation.<ref name=":5" /><ref>{{Cite journal|title = Glacio-epochs and the supercontinent cycle after ~ 3.0&nbsp;Ga: Tectonic boundary conditions for glaciation|journal = Palaeogeography, Palaeoclimatology, Palaeoecology|year=2008 |df=dmy-all |pages = 89–129|volume = 258|issue = 1–2|doi = 10.1016/j.palaeo.2007.09.021|first = N.|last = Eyles|bibcode = 2008PPP...258...89E}}</ref><ref>{{Cite journal|title = Palaeoclimates: the first two billion years|journal = Philosophical Transactions of the Royal Society of London B: Biological Sciences|year=2006 |df=dmy-all |issn = 0962-8436|pmc = 1868609|pmid = 16754607|pages = 917–929|volume = 361|issue = 1470|doi = 10.1098/rstb.2006.1839|first1 = J. F.|last1 = Kasting|first2 = S.|last2 = Ono}}</ref> Though not much oxygen is necessary to sustain the ozone layer, and levels during the Boring Billion may have been high enough for it,<ref>{{cite book|first1=D. C.|last1=Catling|first2=J. F.|last2=Kasting|year=2017|title=Atmospheric Evolution on Inhabited and Lifeless Worlds|publisher=Cambridge University Press|page=291|isbn=978-1-316-82452-8}}</ref> the Earth may have been more heavily bombarded by UV radiation than today.<ref name=Campesi2013/>

==Oceanic composition==
The oceans seem to have had low concentrations of key nutrients thought to be necessary for complex life, namely [[Chemistry:Molybdenum|molybdenum]], iron, [[Chemistry:Nitrogen|nitrogen]], and [[Chemistry:Phosphorus|phosphorus]], in large part due to a lack of oxygen and resultant oxidation necessary for these [[Chemistry:Geochemical cycle|geochemical cycle]]s.<ref>{{Cite journal| last1 = Anbar| first1 = A. D.| last2 = Knoll| first2 = A. H.| year=2002 |df=dmy-all| title = Proterozoic Ocean Chemistry and Evolution: A Bioinorganic Bridge?| journal = Science| volume = 297| issue = 5584| pages = 1137–1142| doi = 10.1126/science.1069651| issn = 0036-8075| pmid = 12183619| bibcode = 2002Sci...297.1137A| citeseerx = 10.1.1.615.3041| s2cid = 5578019}}</ref><ref>{{Cite journal|  last1 = Fennel| first1 = K.| last2 = Follows| first2 = M| last3 = Falkowski| first3 = P. G.| year=2005| title = The co-evolution of the nitrogen, carbon and oxygen cycles in the Proterozoic ocean| journal = American Journal of Science| volume = 305| issue = 6–8| pages = 526–545| doi = 10.2475/ajs.305.6-8.526| issn = 0002-9599| bibcode = 2005AmJS..305..526F| doi-access = free}}</ref><ref>{{cite journal|first1=M. A.|last1=Kipp|first2=E. E.|last2=Stüeken|year=2017|title=Biomass recycling and Earth's early phosphorus cycle|journal=Science Advances|volume=3|issue=11|pages=eaao4795|doi=10.1126/sciadv.aao4795|pmid=29202032|pmc=5706743|bibcode=2017SciA....3O4795K}}</ref> Nutrients could have been more abundant in terrestrial environments, such as lakes or nearshore environments closer to continental runoff.<ref name=Parnell2015>{{cite journal|first1=J.|last1=Parnell|first2=S.|last2=Sprinks|first3=S.|last3=Andrews|first4=W.|last4=Thayalan|first5=S.|last5=Bowden|year=2015|title=High Molybdenum availability for evolution in a Mesoproterozoic lacustrine environment|journal=Nature Communications|volume=6|issue=6996|pages=6996|url=https://www.researchgate.net/publication/276921766|doi=10.1038/ncomms7996|pmid=25988499|bibcode=2015NatCo...6.6996P|doi-access=free|hdl=2164/5221|hdl-access=free}}</ref>

In general, the oceans may have had an oxygenated surface layer, a sulfidic middle layer,<ref name=Canfield1998/><ref name=":3" /><ref name=":7"/> and suboxic bottom layer.<ref name=Slack2009/><ref name=DeBaar1988/> The predominantly sulfidic composition may have caused the oceans to be a black- and milky-turquoise color instead of blue.<ref>{{cite journal|first1=V. A.|last1=Gallardo|first2=C.|last2=Espinoza|year=2008|title=Evolution of ocean color|journal=Proceedings of the International Society for Optical Engineering|volume=7097|pages=1–7|doi=10.1117/12.794742|bibcode=2008SPIE.7097E..0GG|url=https://www.comlsecretariat.org/wp-content/uploads/2010/06/Gallardo-Espinoza-paper-on-the-evolution-of-ocean-color.pdf|series=Instruments, Methods, and Missions for Astrobiology XI|s2cid=53984439|editor1-last=Hoover|editor1-first=Richard B|editor2-last=Levin|editor2-first=Gilbert V|editor3-last=Rozanov|editor3-first=Alexei Y|editor4-last=Davies|editor4-first=Paul C}}</ref>

===Oxygen===
Earth's geologic record indicates two events associated with significant increases in oxygen levels on Earth, with one occurring between 2.4 and 2.1 Ga, known as the [[Earth:Great Oxidation Event|Great Oxidation Event]] (GOE), and the second occurring an approximate 0.8&nbsp;Ga, known as the Neoproterozoic Oxygenation Event (NOE).<ref name=":6">{{Cite journal|title = Oxygen fluctuations stalled life on Earth|year=2014|first=Jane|last=Qiu|url = http://www.nature.com/news/oxygen-fluctuations-stalled-life-on-earth-1.15529|journal = Nature|access-date = 2017-02-24 |df=dmy-all |doi=10.1038/nature.2014.15529|s2cid=131404410}}</ref> The intermediary period, during the Boring Billion, is thought have had low oxygen levels (with minor fluctuations), leading to widespread [[Earth:Anoxic waters|anoxic waters]].<ref name=":3">{{Cite journal|title = The rise of oxygen in Earth's early ocean and atmosphere|year=2014|journal = Nature|pages = 307–315|volume = 506|issue = 7488|doi = 10.1038/nature13068|pmid=24553238|first1 = Timothy W.|last1 = Lyons|first2 = Christopher T.|last2 = Reinhard|first3 = Noah J.|last3 = Planavsky|bibcode = 2014Natur.506..307L|s2cid=4443958}}</ref>

The oceans may have been distinctly stratified, with surface water being oxygenated<ref name=Canfield1998/><ref name=":3" /><ref name=":7"/> and deep water being suboxic (less than 1 μM oxygen),<ref name=DeBaar1988>{{cite journal|last1=De Baar|first1=H. J. W.|last2=German|first2=C. R.|last3=Elderfield|first3=H|last4=van Gaans|first4=P.|year=1988|title=Rare earth element distributions in anoxic waters of the Cariaco Trench|journal=Geochimica et Cosmochimica Acta|volume=52|issue=5|pages=1203–1219|doi=10.1016/0016-7037(88)90275-X|bibcode=1988GeCoA..52.1203D}}</ref> the latter possibly maintained by lower levels of [[Chemistry:Hydrogen|hydrogen]] (H<sub>2</sub>) and H<sub>2</sub>S output by deep sea [[Earth:Hydrothermal vent|hydrothermal vent]]s which otherwise would have been chemically reduced by the oxygen.<ref name=Slack2009/> Even in the shallowest waters, significant quantities of oxygen may have been restricted mainly to areas near the coast.<ref name="DoyleEtAl">{{cite journal |last1=Doyle |first1=Katherine A. |last2=Poulton |first2=Simon W. |last3=Newton |first3=Robert J. |last4=Podkovyrov |first4=Victor N. |last5=Bekker |first5=Andrey |date=October 2018 |title=Shallow water anoxia in the Mesoproterozoic ocean: Evidence from the Bashkir Meganticlinorium, Southern Urals |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926818301992 |journal=Precambrian Research |volume=317 |pages=196–210 |doi=10.1016/j.precamres.2018.09.001 |bibcode=2018PreR..317..196D |s2cid=134378820 |access-date=17 December 2022}}</ref> The [[Medicine:Decomposition|decomposition]] of sinking organic matter would have also leached oxygen from deep waters.<ref name=Johnston2009/><ref name=":3" />

The sudden drop in O<sub>2</sub> after the Great Oxygenation Event—indicated by [[Biology:Δ13C|δ13C]] levels to have been a loss of 10 to 20 times the current volume of atmospheric oxygen—is known as the Lomagundi-Jatuli Event, and is the most prominent [[Physics:Isotopes of carbon|carbon isotope]] event in Earth's history.<ref>{{Cite journal|title = Large-scale fluctuations in Precambrian atmospheric and oceanic oxygen levels from the record of U in shales|journal = Earth and Planetary Science Letters|date = 2013-05-01 |df=dmy-all |pages = 284–293|volume = 369–370|doi = 10.1016/j.epsl.2013.03.031|first1 = C. A.|last1 = Partin|first2 = A.|last2 = Bekker|first3 = N. J.|last3 = Planavsky|first4 = C. T.|last4 = Scott|first5 = B. C.|last5 = Gill|first6 = C.|last6 = Li|first7 = V.|last7 = Podkovyrov|first8 = A.|last8 = Maslov|first9 = K. O.|last9 = Konhauser|bibcode=2013E&PSL.369..284P}}</ref><ref>{{Cite journal|title = Oxygen overshoot and recovery during the early Paleoproterozoic|journal = Earth and Planetary Science Letters|date = 2012-02-01 |df=dmy-all |pages = 295–304|volume = 317–318|doi = 10.1016/j.epsl.2011.12.012|first1 = A.|last1 = Bekker|first2 = H. D.|last2 = Holland|bibcode=2012E&PSL.317..295B}}</ref><ref>{{Cite journal|title = Rise in seawater sulphate concentration associated with the Paleoproterozoic positive carbon isotope excursion: evidence from sulphate evaporites in the ~2.2–2.1 Gyr shallow-marine Lucknow Formation, South Africa|journal = Terra Nova|date = 2008-04-01 |df=dmy-all |issn = 1365-3121|pages = 108–117|volume = 20|issue = 2|doi = 10.1111/j.1365-3121.2008.00795.x|language = en|first1 = S.|last1 = Schröder|first2 = A.|last2 = Bekker|first3 = N. J.|last3 = Beukes|first4 = H.|last4 = Strauss|first5 = H. S.|last5 = Van Niekerk|bibcode = 2008TeNov..20..108S|doi-access = free}}</ref> Oxygen levels may have been less than 0.1 to 1% of modern-day levels,<ref>{{cite journal |last1=Hardisty |first1=Dalton S. |last2=Lu |first2=Zunli |last3=Bekker |first3=Andrey |last4=Diamond |first4=Charles W. |last5=Gill |first5=Benjamin C. |last6=Jiang |first6=Ganqing |last7=Kah |first7=Linda C. |last8=Knoll |first8=Andrew H. |last9=Lloyd |first9=Sean J. |last10=Osburn |first10=Magdalena R. |last11=Planavsky |first11=Noah J. |last12=Wang |first12=Chunjiang |last13=Zhou |first13=Xiaoli |last14=Lyons |first14=Timothy W. |date=1 April 2017 |title=Perspectives on Proterozoic surface ocean redox from iodine contents in ancient and recent carbonate |journal=[[Earth:Earth and Planetary Science Letters|Earth and Planetary Science Letters]] |volume=463 |pages=159–170 |doi=10.1016/j.epsl.2017.01.032 |bibcode=2017E&PSL.463..159H |s2cid=13136821 |doi-access=free |hdl=1912/8872 |hdl-access=free }}</ref> which would have effectively stalled the evolution of complex life during the Boring Billion.<ref name=":6" /><ref name=":7" /> However, a Mesoproterozoic Oxygenation Event (MOE), during which oxygen rose transiently to about 4% PAL at various points in time, is proposed to have occurred from 1.59 to 1.36 Ga.<ref>{{cite journal |last1=Zhang |first1=Shuichang |last2=Wang |first2=Huajian |last3=Wang |first3=Xiaomei |last4=Ye |first4=Yuntao |date=25 October 2021 |title=The Mesoproterozoic Oxygenation Event |url=https://link.springer.com/article/10.1007/s11430-020-9825-x?idp_error=cookies_not_supported&error=cookies_not_supported&code=d00a2df1-dd21-4c70-9125-9588afcda877 |journal=Science China Earth Sciences |volume=64 |issue=12 |pages=2043–2068 |doi=10.1007/s11430-020-9825-x |bibcode=2021ScChD..64.2043Z |s2cid=239891560 |access-date=9 May 2023}}</ref> In particular, some evidence from the Gaoyuzhuang Formation suggests a rise in oxygen around 1.57 Ga,<ref>{{Cite journal |last1=Ye |first1=Yuntao |last2=Wang |first2=Huajian |last3=Wang |first3=Xiaomei |last4=Li |first4=Jie |last5=Wu |first5=Chaodong |last6=Zhang |first6=Shuichang |date=1 May 2023 |title=Regional and global proxies for varying ocean redox conditions at ∼1.57 Ga: A causal connection with volcanism-induced weathering |journal=Geosystems and Geoenvironment |volume=2 |issue=2 |pages=100173 |doi=10.1016/j.geogeo.2022.100173 |bibcode=2023GsGe....200173Y |issn=2772-8838 |doi-access=free }}</ref> while the Velkerri Formation in the Roper Group of the Northern Territory of {{wipe|Australia}},<ref name="MukherjeeLarge2016" /> the Kaltasy Formation ({{lang-ru|Калтасинская свита}}) of Volgo-Uralia, {{wipe|Russia}},<ref name="DoyleEtAl" /> and the Xiamaling Formation in the northern [[Earth:North China Craton|North China Craton]]<ref>{{cite journal |last1=He |first1=Yuting |last2=Zhu |first2=Xiyan |last3=Qiu |first3=Yifan |last4=Pang |first4=Lanyin |last5=Zhao |first5=Taiping |date=December 2022 |title=Extreme climate changes influenced early life evolution at ~ 1.4 Ga: Implications from shales of the Xiamaling Formation, northern North China Craton |url=https://www.sciencedirect.com/science/article/abs/pii/S030192682200345X |journal=Precambrian Research |volume=383 |page=106901 |doi=10.1016/j.precamres.2022.106901 |bibcode=2022PreR..38306901H |s2cid=253787177 |access-date=17 December 2022}}</ref><ref>{{Cite journal |last1=Liu |first1=Anqi |last2=Tang |first2=Dongjie |last3=Shi |first3=Xiaoying |last4=Zhou |first4=Xiqiang |last5=Zhou |first5=Limin |last6=Shang |first6=Mohan |last7=Li |first7=Yang |last8=Fang |first8=Hao |date=1 June 2020 |title=Mesoproterozoic oxygenated deep seawater recorded by early diagenetic carbonate concretions from the Member IV of the Xiamaling Formation, North China |url=https://www.sciencedirect.com/science/article/pii/S0301926819303626 |journal=Precambrian Research |volume=341 |pages=105667 |doi=10.1016/j.precamres.2020.105667 |bibcode=2020PreR..34105667L |s2cid=212948463 |issn=0301-9268 |access-date=11 September 2023}}</ref> indicate noticeable oxygenation around 1.4 Ga, although the degree to which this represents global oxygen levels is unclear.<ref name="MukherjeeLarge2016">{{cite journal |last1=Mukherjee |first1=Indrani |last2=Large |first2=Ross R. |date=August 2016 |title=Pyrite trace element chemistry of the Velkerri Formation, Roper Group, McArthur Basin: Evidence for atmospheric oxygenation during the Boring Billion |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926816301255 |journal=Precambrian Research |volume=281 |pages=13–26 |doi=10.1016/j.precamres.2016.05.003 |bibcode=2016PreR..281...13M |access-date=8 November 2022}}</ref> Oxic conditions would have become dominant at the NOE causing the proliferation of [[Biology:Aerobic organism|aerobic]] activity over [[Biology:Anaerobic organism|anaerobic]],<ref name=Canfield1998/><ref name=":3" /><ref name=Johnston2009/> but widespread suboxic and anoxic conditions likely lasted until about 0.55 Ga corresponding with [[Earth:Ediacaran biota|Ediacaran biota]] and the [[Earth:Cambrian explosion|Cambrian explosion]].<ref>{{cite journal|first1=L. C.|last1=Kah|first2=T. W.|last2=Lyons|first3=T. D.|last3=Frank|year=2004|title=Low marine sulphate and protracted oxygenation of the Proterozoic biosphere|journal=Nature|volume=438|issue=7010|pages=834–838|doi=10.1038/nature02974|pmid=15483609|bibcode=2004Natur.431..834K|s2cid=4404486|url=https://digitalcommons.unl.edu/geosciencefacpub/99}}</ref><ref>{{cite journal|first1=L. M.|last1=Och|first2=G. A.|last2=Shields-Zhou|year=2012|title=The Neoproterozoic oxygenation event: Environmental perturbations and biogeochemical cycling|journal=Earth-Science Reviews|volume=110|issue=1–4|pages=26–57|doi=10.1016/j.earscirev.2011.09.004|bibcode=2012ESRv..110...26O}}</ref>

===Sulfur===
[[File:How oceans become euxinic.png|thumb|upright=2|Diagram of how euxinic conditions form]]
In 1998, geologist Donald Canfield proposed what is now known as the [[Earth:Canfield ocean|Canfield ocean]] hypothesis. Canfield claimed that increasing levels of oxygen in the atmosphere at the Great Oxygenation Event would have reacted with and oxidized continental iron pyrite (FeS<sub>2</sub>) deposits, with [[Chemistry:Sulfate|sulfate]] (SO<sub>4</sub><sup>2−</sup>) as a byproduct, which was transported into the sea. [[Earth:Sulfate-reducing microorganisms|Sulfate-reducing microorganisms]] converted this to [[Chemistry:Hydrogen sulfide|hydrogen sulfide]] (H<sub>2</sub>S), dividing the ocean into a somewhat oxic surface layer, and a sulfidic layer beneath, with [[Biology:Anoxygenic photosynthesis|anoxygenic]] bacteria living at the border, metabolizing the H<sub>2</sub>S and creating sulfur as a waste product. This created widespread euxinic conditions in middle-waters, an anoxic state with a high sulfur concentration, which was maintained by the bacteria.<ref name=":3" /><ref>{{Cite journal| last1 = Lyons| first1 = Timothy W.| last2 = Reinhard| first2 = Christopher T.| year=2009 |df=dmy-all| title = An early productive ocean unfit for aerobics| journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 106| issue = 43
 |pages = 18045–18046| doi = 10.1073/pnas.0910345106| issn = 0027-8424| pmc = 2775325| pmid = 19846788| bibcode = 2009PNAS..10618045L| doi-access = free}}</ref><ref name=Canfield1998>{{Cite journal| last = Canfield| first = D. E.
| year=1998|df=dmy-all| title = A new model for Proterozoic ocean chemistry| journal = Nature| volume = 396| issue = 6710| pages = 450–453| doi = 10.1038/24839| issn = 0028-0836| bibcode = 1998Natur.396..450C| s2cid = 4414140
}}</ref><ref>{{Cite book|title = Biodiversity and Earth History|url = https://books.google.com/books?id=ct29BwAAQBAJ|publisher = Springer|year=2015|isbn = 978-3-662-46394-9|first1 = J.|last1 = Boenigk|first2 = S.|last2 = Wodniok|first3 = E.|last3 = Glücksman|pages=58–59}}</ref><ref name=Johnston2009>{{Cite journal|title = Anoxygenic photosynthesis modulated Proterozoic oxygen and sustained Earth's middle age|last = Johnston|first = D. T. |year=2009 |journal = Proceedings of the National Academy of Sciences of the United States of America|doi = 10.1073/pnas.0909248106 |pmid = 19805080|pmc = 2753640|volume=106|issue = 40|pages=16925–16929|bibcode =2009PNAS..10616925J|doi-access = free}}</ref><ref name=":7">{{cite journal |first1=R. |last1=Large |first2=J. A. |last2=Halpin |first3=L. V. |last3=Danyushevsky |year=2014 |title=Trace element content of sedimentary pyrite as a new proxy for deep-time ocean–atmosphere evolution |journal=[[Earth:Earth and Planetary Science Letters|Earth and Planetary Science Letters]] |volume=389 |pages=209–220 |doi=10.1016/j.epsl.2013.12.020 |bibcode=2014E&PSL.389..209L}}</ref><ref>{{cite journal |last1=Wu |first1=Yaowei |last2=Tian |first2=Hui |last3=Yin |first3=Runsheng |last4=Chen |first4=Di |last5=Grasby |first5=Stephen E. |last6=Shen |first6=Jun |last7=Li |first7=Tengfei |last8=Ji |first8=Sui |last9=Peng |first9=Ping'an |date=15 August 2023 |title=Highly fractionated Hg isotope evidence for dynamic euxinia in shallow waters of the Mesoproterozoic ocean |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X23002248 |journal=[[Earth:Earth and Planetary Science Letters|Earth and Planetary Science Letters]] |volume=616 |page=118211 |doi=10.1016/j.epsl.2023.118211 |bibcode=2023E&PSL.61618211W |s2cid=259004695 |access-date=3 July 2023}}</ref><ref>{{Cite journal |last1=Zheng |first1=Wang |last2=Gilleaudeau |first2=Geoffrey J. |last3=Kah |first3=Linda C. |last4=Anbar |first4=Ariel D. |date=16 October 2018 |title=Mercury isotope signatures record photic zone euxinia in the Mesoproterozoic ocean |journal=Proceedings of the National Academy of Sciences of the United States of America |language=en |volume=115 |issue=42 |pages=10594–10599 |doi=10.1073/pnas.1721733115 |issn=0027-8424 |pmc=6196510 |pmid=30275325 |bibcode=2018PNAS..11510594Z |doi-access=free }}</ref> However, more systematic geochemical study of the Mid-Proterozoic indicates that the oceans were largely ferruginous with a thin surface layer of weakly oxygenated waters, and euxinia may have occurred over relatively small areas, perhaps less than 7% of the seafloor.<ref>{{Cite journal |last1=Gilleaudeau |first1=Geoffrey J. |last2=Romaniello |first2=Stephen J. |last3=Luo |first3=Genming |last4=Kaufman |first4=Alan J. |last5=Zhang |first5=Feifei |last6=Klaebe |first6=Robert M. |last7=Kah |first7=Linda C. |last8=Azmy |first8=Karem |last9=Bartley |first9=Julie K. |last10=Zheng |first10=Wang |last11=Knoll |first11=Andrew H. |last12=Anbar |first12=Ariel D. |date=2019-09-01 |title=Uranium isotope evidence for limited euxinia in mid-Proterozoic oceans |journal=[[Earth:Earth and Planetary Science Letters|Earth and Planetary Science Letters]] |language=en |volume=521 |pages=150–157 |doi=10.1016/j.epsl.2019.06.012 |bibcode=2019E&PSL.521..150G |s2cid=198401867 |issn=0012-821X|doi-access=free }}</ref><ref>{{Cite journal |last1=Planavsky |first1=Noah J. |last2=McGoldrick |first2=Peter |last3=Scott |first3=Clinton T. |last4=Li |first4=Chao |last5=Reinhard |first5=Christopher T. |last6=Kelly |first6=Amy E. |last7=Chu |first7=Xuelei |last8=Bekker |first8=Andrey |last9=Love |first9=Gordon D. |last10=Lyons |first10=Timothy W. |date=September 2011 |title=Widespread iron-rich conditions in the mid-Proterozoic ocean |url=https://www.nature.com/articles/nature10327 |journal=Nature |language=en |volume=477 |issue=7365 |pages=448–451 |doi=10.1038/nature10327 |pmid=21900895 |bibcode=2011Natur.477..448P |s2cid=205225926 |issn=1476-4687}}</ref>

===Iron===
Among rocks dating to the Boring Billion, there is a conspicuous lack of [[Earth:Banded iron formation|banded iron formation]]s, which form from iron in the upper water column (sourced from the deep ocean) reacting with oxygen and precipitating out of the water. They seemingly cease around the world after 1.85 Ga. Canfield argued that oceanic SO<sub>4</sub><sup>2−</sup> [[Chemistry:Redox|reduced]] all the iron in the anoxic deep sea.<ref name=Canfield1998/> Iron could have been metabolized by anoxygenic bacteria.<ref name=Canfield2018/> It has also been proposed that the 1.85 Ga [[Earth:Sudbury Basin|Sudbury meteor impact]] mixed the previously stratified ocean via tsunamis, interaction between vaporized seawater and the oxygenated atmosphere, oceanic [[Physics:Cavitation|cavitation]], and massive runoff of destroyed [[Earth:Continental margin|continental margin]]s into the sea. Resultant suboxic deep waters (due to oxygenated surface water mixing with previously anoxic deep water) would have oxidized deep-water iron, preventing it from being transported and deposited on continental margins.<ref name=Slack2009>{{cite journal|first1=J. F.|last1=Slack|first2=W. F.|last2=Cannon|year=2009|title=Extraterrestrial demise of banded iron formations 1.85 billion years ago|journal=Geology|volume=37|issue=11|pages=1011–1014|doi=10.1130/G30259A.1|bibcode=2009Geo....37.1011S}}</ref>

Nonetheless, iron-rich waters did exist, such as the 1.4 Ga Xiamaling Formation of Northern China, which perhaps was fed by deep water hydrothermal vents. Iron-rich conditions also indicate anoxic bottom water in this area, as oxic conditions would have oxidized all the iron.<ref name=Canfield2018>{{cite journal|first1=D. E.|last1=Canfield|first2=S.|last2=Zhang|first3=H.|last3=Wang|first4=X.|last4=Wang|first5=W.|last5=Zhao|first6=J.|last6=Su|first7=C. J.|last7=Bjerrum|first8=E. R.|last8=Haxen|first9=E. U.|last9=Hammarlund|year=2018|title=A Mesoproterozoic iron formation|journal=Proceedings of the National Academy of Sciences|volume=115|issue=17|pages=3895–3904|doi=10.1073/pnas.1720529115|pmid=29632173|pmc=5924912|bibcode=2018PNAS..115E3895C|doi-access=free}}</ref>

==Lifeforms==
Low nutrient abundance may have facilitated [[Earth:Symbiosis|photosymbiosis]]—where one organism is capable of photosynthesis and the other metabolizes the waste product—among [[Biology:Prokaryote|prokaryote]]s ([[Biology:Bacteria|bacteria]] and [[Biology:Archaea|archaea]]), and the emergence of [[Biology:Eukaryote|eukaryote]]s. Bacteria, Archaea, and Eukaryota are the three domains, the highest taxonomic ranking. Eukaryotes are distinguished from prokaryotes by a [[Biology:Cell nucleus|nucleus]] and membrane-bound organelles, and almost all multicellular organisms are eukaryotes.<ref name=Brasier1998>{{cite journal|first1=M. D.|last1=Brasier|first2=J. F.|last2=Lindsay|year=1998|title=A billion years of environmental stability and the emergence of eukaryotes: new data from northern Australia|journal=Geology|volume=26|issue=6|pages=555–558|doi=10.1130/0091-7613(1998)026<0555:ABYOES>2.3.CO;2|pmid=11541449|bibcode=1998Geo....26..555B}}</ref>

{{also|Volyn biota}} <!-- sorry I dont know how to incorporate its text here-->

===Prokaryotes===
[[File:Stromatolites, Belt Supergroup, Glacier National Park.jpg|thumb|1.44 Ga stromatolite from Glacier National Park, Montana]]
Prokaryotes were the dominant lifeforms throughout the Boring Billion.<ref name=":10" /><ref name=Gueneli/><ref name=Canfield1998/> Microfossils indicate the presence of cyanobacteria, [[Biology:Green sulfur bacteria|green]] and [[Biology:Purple sulfur bacteria|purple]] sulfur bacteria, methane-producing archaea, sulfate-metabolizing bacteria, [[Biology:Methanotroph|methane-metabolizing]] archaea or bacteria, iron-metabolizing bacteria, [[Biology:Denitrifying bacteria|nitrogen-metabolizing]] bacteria, and anoxygenic photosynthetic bacteria.<ref name=Javaux2018/>

Anoxygenic cyanobacteria are thought to have been the dominant photosynthesizers, metabolizing the abundant H<sub>2</sub>S in the oceans. In iron-rich waters, cyanobacteria may have suffered from [[Chemistry:Iron poisoning|iron poisoning]], especially in offshore waters where iron-rich deep water mixed with surface waters, and thus were outcompeted by other bacteria which could metabolize both iron and H<sub>2</sub>S. However, iron poisoning could have been abated by [[Chemistry:Silica|silica]]-rich waters or [[Earth:Biomineralization|biomineralization]] of iron within the cell.<ref name=Javaux2018>{{cite journal|first1=E. J.|last1=Javaux|first2=K.|last2=Lepot|year=2018|title=The Paleoproterozoic fossil record: Implications for the evolution of the biosphere during Earth's middle-age|journal=Earth-Science Reviews|volume=176|pages=68–86|doi=10.1016/j.earscirev.2017.10.001|bibcode=2018ESRv..176...68J|doi-access=free|hdl=20.500.12210/62416|hdl-access=free}}</ref>

Unicellular planktonic lineages of cyanobacteria evolved in freshwater during the middle of the [[Earth:Mesoproterozoic|Mesoproterozoic]], and during the [[Earth:Neoproterozoic|Neoproterozoic]] both benthic marine and some freshwater ancestors gave rise to marine planktonic cyanobacteria (both nitrogen-fixing and non-nitrogen fixing), contributing to the oxygenation of the Pre-Cambrian oceans.<ref>[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4665016/ Origin of marine planktonic cyanobacteria - PMC - NCBI]</ref><ref>[https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/cyanobacterial-evolution-during-the-precambrian/7BD85D3DBE415BED2F4C359632030E74 Cyanobacterial evolution during the Precambrian]</ref>

Research on cyanobacteria in the laboratory has shown that the enzyme nitrogenase, which is used to fix atmospheric nitrogen, stops working when the oxygen levels is higher than 10% of current atmospheric levels. The absence of nitrogen due to an increased amount of oxygen would have created a negative feedback loop where atmospheric oxygen levels stabilised at 2%, which began to change about 600 million years ago when landplants started releasing oxygen. By 408 million years ago, nitrogen fixating cyanobacteria had evolved heterocysts to protect their nitrogenase from oxygen.<ref>[https://www.ucl.ac.uk/news/2019/aug/early-life-earth-limited-enzyme Early life on Earth limited by enzyme | UCL News]</ref><ref>[https://www.cell.com/trends/plant-science/fulltext/S1360-1385(19)30186-4 Nitrogenase Inhibition Limited Oxygenation of Earth's Proterozoic Atmosphere]</ref>

===Eukaryotes===
Eukaryotes may have arisen around the beginning of the Boring Billion,<ref name=Mukherjee2018/> coinciding with the accretion of Columbia, which could have somehow increased oceanic oxygen levels.<ref name=Brooke2014/> Although there have been claimed records of eukaryotes as early as 2.1 billion years ago, these have been considered questionable, with the oldest unambiguous eukaryote remains dating to around 1.8-1.6 billion years ago in China.<ref>{{Cite journal |last1=Fakhraee |first1=Mojtaba |last2=Tarhan |first2=Lidya G. |last3=Reinhard |first3=Christopher T. |last4=Crowe |first4=Sean A. |last5=Lyons |first5=Timothy W. |last6=Planavsky |first6=Noah J. |date=May 2023 |title=Earth's surface oxygenation and the rise of eukaryotic life: Relationships to the Lomagundi positive carbon isotope excursion revisited |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825223000879 |journal=Earth-Science Reviews |language=en |volume=240 |pages=104398 |doi=10.1016/j.earscirev.2023.104398|bibcode=2023ESRv..24004398F |s2cid=257761993 }}</ref> Following this, eukaryotic evolution was rather slow,<ref name=":10" /> possibly due to the euxinic conditions of the Canfield ocean and a lack of key nutrients and metals<ref name=":1" /><ref name=Mukherjee2018/> which prevented large, complex life with high energy requirements from evolving.<ref name=":5">{{Cite journal|title = Low Mid-Proterozoic atmospheric oxygen levels and the delayed rise of animals|journal = Science|date = 2014-10-31 |df=dmy-all |issn = 0036-8075|pmid = 25359975|pages = 635–638|volume = 346|issue = 6209|doi = 10.1126/science.1258410|language = en|first1 = Noah J.|last1 = Planavsky|first2 = Christopher T.|last2 = Reinhard|first3 = Xiangli|last3 = Wang|first4 = Danielle|last4 = Thomson|first5 = Peter|last5 = McGoldrick|first6 = Robert H.|last6 = Rainbird|first7 = Thomas|last7 = Johnson|first8 = Woodward W.|last8 = Fischer|first9 = Timothy W.|last9 = Lyons|bibcode = 2014Sci...346..635P|s2cid = 37395258|url = https://authors.library.caltech.edu/50325/13/Planavsky.SM.pdf}}</ref> Euxinic conditions would have also decreased the solubility of iron<ref name=Canfield1998/> and [[Chemistry:Molybdenum|molybdenum]],<ref>{{Cite journal| last1 = Reinhard| first1 = C. T.| last2 = Planavsky| first2 = N. J.| last3 = Robbins| first3 = L. J.| last4 = Partin| first4 = C. A.| last5 = Gill| first5 = B. C.| last6 = Lalonde| first6 = S. V.| last7 = Bekker| first7 = A.| last8 = Konhauser| first8 = K. O.| last9 = Lyons| first9 = T. W.| year=2013|df=dmy-all | title = Proterozoic ocean redox and biogeochemical stasis| journal = Proceedings of the National Academy of Sciences| volume = 110| issue = 14| pages = 5357–5362| doi = 10.1073/pnas.1208622110| issn = 0027-8424| pmc = 3619314| pmid = 23515332| bibcode = 2013PNAS..110.5357R| doi-access = free}}</ref> essential metals in [[Biology:Nitrogen fixation|nitrogen fixation]]. A lack of dissolved nitrogen would have favored prokaryotes over eukaryotes, as the former can metabolize gaseous nitrogen.<ref name=":8">{{Cite journal| last = Anbar| first = A. D.| year=2002 |df=dmy-all | title = Proterozoic ocean chemistry and evolution: a bioinorganic bridge| journal = Science| volume = 297| issue = 5584| pages = 1137–1142| doi = 10.1126/science.1069651| pmid = 12183619| bibcode = 2002Sci...297.1137A| s2cid = 5578019}}</ref> An alternative hypothesis for the lack of diversification among eukaryotes implicates high temperatures during the Boring Billion rather than low oxygen levels, positing that the fact that oxygenation events prior to the Late Neoproterozoic did not kickstart eukaryotic evolution suggests it was not the main limiting factor inhibiting it.<ref>{{cite journal |last1=Zhang |first1=Fenglian |last2=Wang |first2=Huaijan |last3=Ye |first3=Yuntao |last4=Liu |first4=Yuke |last5=Lyu |first5=Yitong |last6=Deng |first6=Yan |last7=Lyu |first7=Dan |last8=Wang |first8=Xiaomei |last9=Wu |first9=Huaichun |last10=Deng |first10=Shenghui |last11=Zhang |first11=Shuichang |date=15 August 2022 |title=Did high temperature rather than low O2 hinder the evolution of eukaryotes in the Precambrian? |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926822001991 |journal=Precambrian Research |volume=378 |page=106755 |doi=10.1016/j.precamres.2022.106755 |bibcode=2022PreR..37806755Z |s2cid=249584466 |access-date=29 April 2023}}</ref>

[[File:Ramathallus lobatus.png|thumb|left|upright|1.6 Ga ''[[Biology:Ramathallus|Ramathallus]]'' fossil, the earliest known red alga<ref name=Bengtson2017/>]]
Nonetheless, the diversification of [[Biology:Crown group|crown group]] eukaryotic macroorganisms seems to have started about 1.6–1 Ga, seemingly coinciding with an increase in key nutrient concentrations.<ref name=Mukherjee2018/> According to [[Biology:Molecular clock|molecular clock]] analysis, plants diverged from animals and fungi about 1.6 Ga; animals and fungi about 1.5 Ga; [[Biology:Bilateria|Bilateria]]ns and [[Biology:Cnidaria|cnidaria]]ns (animals respectively with and without bilateral symmetry) about 1.3 Ga; [[Biology:Sponge|sponge]]s 1.35 Ga;<ref name=Hedges2004/> and [[Biology:Ascomycota|Ascomycota]] and [[Biology:Basidiomycota|Basidiomycota]] (the two divisions of the fungus subkingdom Dikarya) 0.97 Ga.<ref name=Hedges2004/>  The paper's authors state that their time estimates disagree with the scientific consensus.

Fossils from the late Palaeoproterozoic and early Mesoproterozoic of the Vindhyan sedimentary basin of India, the Ruyang Group of China, and the Kotuikan Formation of the [[Earth:Anabar Shield|Anabar Shield]] of Siberia indicate high rates (by pre-Ediacaran standards) of eukaryotic diversification between 1.7 and 1.4 Ga, although much of this diversity is represented by previously unknown, no longer existing clades of eukaryotes.<ref>{{cite journal|first1=S.|last1=Bengtson|first2=V.|last2=Belivanova|first3=B.|last3=Rasmussen|first4=M.|last4=Whitehouse|year=2009|title=The controversial "Cambrian" fossils of the Vindhyan are real but more than a billion years older|journal=Proceedings of the National Academy of Sciences|volume=106|issue=19|pages=7729–7734|doi=10.1073/pnas.0812460106|pmid=19416859|pmc=2683128|bibcode=2009PNAS..106.7729B|doi-access=free}}</ref><ref>{{cite journal |last1=Agić |first1=Heda |last2=Moczydłowska |first2=Małgorzata |last3=Yin |first3=Leiming |date=August 2017 |title=Diversity of organic-walled microfossils from the early Mesoproterozoic Ruyang Group, North China Craton – A window into the early eukaryote evolution |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926817300384#! |journal=Precambrian Research |volume=297 |pages=101–130 |doi=10.1016/j.precamres.2017.04.042 |bibcode=2017PreR..297..101A |access-date=13 October 2022}}</ref><ref>{{cite journal |last1=Leiming |first1=Yin |last2=Xunlai |first2=Yuan |last3=Fanwei |first3=Meng |last4=Jie |first4=Hu |date=7 November 2005 |title=Protists of the Upper Mesoproterozoic Ruyang Group in Shanxi Province, China |url=https://www.sciencedirect.com/science/article/abs/pii/S030192680500118X |journal=Precambrian Research |volume=141 |issue=1–2 |pages=49–66 |doi=10.1016/j.precamres.2005.08.001 |bibcode=2005PreR..141...49L |access-date=13 October 2022}}</ref><ref>{{cite journal |last1=Leiming |first1=Yin |last2=Bian |first2=Lizeng |last3=Xunlai |first3=Yuan |date=October 2004 |title=Discovery of branched tubular algae and microscopic tubes with annular-helical thickening from the Mesoproterozoic Ruyang Group of Shanxi, North China |url=https://link.springer.com/article/10.1360/02yd0356 |journal=Science China Earth Sciences |volume=47 |issue=10 |pages=880–885 |doi=10.1360/02yd0356 |s2cid=129336775 |access-date=13 October 2022}}</ref><ref>{{cite journal |last1=Pang |first1=Ke |last2=Tang |first2=Qing |last3=Yuan |first3=Xun-Lai |last4=Wan |first4=Bin |last5=Xiao |first5=Shuhai |date=September 2015 |title=A biomechanical analysis of the early eukaryotic fossil Valeria and new occurrence of organic-walled microfossils from the Paleo-Mesoproterozoic Ruyang Group |journal=Palaeoworld |volume=24 |issue=3 |pages=251–262 |doi=10.1016/j.palwor.2015.04.002 |doi-access=free }}</ref><ref>{{cite journal |last1=Vorob’eva |first1=Natalya G. |last2=Sergeev |first2=Vladimir N. |last3=Petrov |first3=Peter Y. |date=January 2015 |title=Kotuikan Formation assemblage: A diverse organic-walled microbiota in the Mesoproterozoic Anabar succession, northern Siberia |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926814003866#! |journal=Precambrian Research |volume=256 |pages=201–222 |doi=10.1016/j.precamres.2014.11.011 |bibcode=2015PreR..256..201V |access-date=15 October 2022}}</ref> The earliest known [[Biology:Red algae|red algae]] mats date to 1.6 Ga.<ref name=Bengtson2017>{{cite journal|first1=S.|last1=Bengtson|first2=T.|last2=Sallstedt|first3=V.|last3=Belivanova|first4=M.|last4=Whitehouse|year=2017|title=Three-dimensional preservation of cellular and subcellular structures suggests 1.6 billion-year-old crown-group red algae|journal=PLOS Biology|volume=15|issue=3|page=e2000735|doi=10.1371/journal.pbio.2000735|pmc=5349422|pmid=28291791 |doi-access=free }}</ref> The earliest known fungus dates to 1.01–0.89 Ga from Northern Canada.<ref name=Loron2019>{{cite journal|first1=C. C.|last1=Loron|first2=C.|last2=François|first3=R. H.|last3=Rainbird|first4=E. C.|last4=Turner|first5=S.|last5=Borensztajn|first6=E. J.|last6=Javaux|year=2019|title=Early fungi from the Proterozoic era in Arctic Canada|journal=Nature|volume=70|pages=232–235|issue=7760|url=https://www.researchgate.net/publication/333301933|doi=10.1038/s41586-019-1217-0|pmid=31118507|bibcode=2019Natur.570..232L|s2cid=162180486}}</ref> Multicellular eukaryotes, thought to be the descendants of colonial unicellular aggregates, had probably evolved about 2–1.4 Ga.<ref>{{cite book|first=G. M.|last=Cooper|year=2000|chapter=The Origin and Evolution of Cells|title=The Cell: A Molecular Approach|edition=2nd|publisher=Sinauer Associates|chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK9841/}}</ref><ref>{{cite journal|last=Niklas|first=K. J.|year=2014|title=The evolutionary-developmental origins of multicellularity|journal=American Journal of Botany |volume=101|issue=1|pages=6–25|doi=10.3732/ajb.1300314|pmid=24363320}}</ref> Likewise, early multicellular eukaryotes likely mainly aggregated into [[Earth:Stromatolite|stromatolite]] mats.<ref name=Brooke2014>{{cite book|first=J. L.|last=Brooke|year=2014|title=Climate Change and the Course of Global History: A Rough Journey|publisher=Cambridge University Press|pages=40–42|isbn=978-0-521-87164-8}}</ref>

The red alga ''[[Biology:Bangiomorpha|Bangiomorpha]]'' is the earliest known sexually reproducing and [[Biology:Meiosis|meiotic]] lifeform,<ref>{{Cite book |chapter-url=https://www.researchgate.net/publication/285932986 |chapter=DNA Repair as the Primary Adaptive Function of Sex in Bacteria and Eukaryotes |pages=1–49 |df=dmy-all |archive-url=https://web.archive.org/web/20131029202307/https://www.novapublishers.com/catalog/product_info.php?products_id=31918 |archive-date=2013-10-29 |url-status=dead|last1=Bernstein|first1=H.|last2=Bernstein|first2=C.|last3=Michod|first3=R. E.|editor1-last=Kimura| editor1-first=S.|editor2-last=Shimizu|editor2-first=S.|publisher=Nova Biomedical|isbn=978-1-62100-756-2|title=DNA Repair: New Research|date=2012}}</ref> and evolved by 1.047 Ga.<ref>{{Cite journal |last1=Gibson |first1=Timothy M. |last2=Shih |first2=Patrick M. |last3=Cumming |first3=Vivien M. |last4=Fischer |first4=Woodward W. |last5=Crockford |first5=Peter W. |last6=Hodgskiss |first6=Malcolm S.W. |last7=Wörndle |first7=Sarah |last8=Creaser |first8=Robert A. |last9=Rainbird |first9=Robert H. |last10=Skulski |first10=Thomas M. |last11=Halverson |first11=Galen P. |date=2017-12-08 |title=Precise age of Bangiomorpha pubescens dates the origin of eukaryotic photosynthesis |url=https://doi.org/10.1130/G39829.1 |journal=Geology |volume=46 |issue=2 |pages=135–138 |doi=10.1130/g39829.1 |issn=0091-7613}}</ref> Based on this, these adaptations evolved between ca. 2–1.4 Ga.<ref name=Mukherjee2018>{{cite journal|first1=I.|last1=Mukherjee|first2=R. R.|last2=Large|first3=R.|last3=Corkrey|first4=L. V.|last4=Danyushevsky|year=2018|title=The Boring Billion, a slingshot for Complex Life on Earth|journal=Scientific Reports|volume=8|issue=4432|pages=4432|doi=10.1038/s41598-018-22695-x|pmid=29535324|pmc=5849639|bibcode=2018NatSR...8.4432M}}</ref> Alternatively, these may have evolved well before the last common ancestor of eukaryotes given that meiosis is performed using the same proteins in all eukaryotes, perhaps stretching to as far back as the hypothesized [[Biology:RNA world|RNA world]].<ref>{{cite journal|first1=R.|last1=Egel|first2=D.|last2=Penny|year=2007|title=On the Origin of Meiosis in Eukaryotic Evolution: Coevolution of Meiosis and Mitosis from Feeble Beginnings|journal=Genome Dynamics and Stability|volume=3|issue=249–288|pages=249–288|doi=10.1007/7050_2007_036|url=https://www.researchgate.net/publication/226518084|isbn=978-3-540-68983-6}}</ref>

Cell [[Biology:Organelle|organelle]]s probably originated from free-living [[Biology:Cyanobacteria|cyanobacteria]] ([[Biology:Symbiogenesis|symbiogenesis]])<ref name=":10" /><ref name=":11" /><ref>{{cite journal |title=Endosymbiotic gene transfer: organelle genomes forge eukaryotic chromosomes|journal=Nature Reviews Genetics|year=2004|pages=123–135|volume=5|issue=2|doi=10.1038/nrg1271|first1=J. N.|last1=Timmis|first2=Michael A.|last2=Ayliffe|first3=C. Y.|last3=Huang|first4=W.|last4=Martin|pmid=14735123|s2cid=2385111}}</ref><ref name=Mukherjee2018/> possibly after the evolution of [[Biology:Phagocytosis|phagocytosis]] (engulfing other cells) with the removal of the rigid [[Biology:Cell wall|cell wall]] which was only necessary for asexual reproduction.<ref name=":10" /> [[Biology:Mitochondria|Mitochondria]] had already evolved in the Great Oxygenation Event, but [[Biology:Plastid|plastid]]s used in [[Biology:Archaeplastida|primoplants]] for [[Earth:Photosynthesis|photosynthesis]] are thought to have appeared about 1.6–1.5 Ga.<ref name=Hedges2004>{{cite journal|first1=S. B.|last1=Hedges|first2=J. E.|last2=Blair|first3=M. L.|last3=Venturi|first4=J. L.|last4=Shoe|year=2004|title=A molecular timescale of eukaryote evolution and the rise of complex multicellular life|journal=BMC Evolutionary Biology|volume=4|issue=2|pages=2|doi=10.1186/1471-2148-4-2|pmc=341452|pmid=15005799 |doi-access=free }}</ref> [[Biology:Histone|Histone]]s likely appeared during the Boring Billion to help organize and package the increasing amount of DNA in eukaryotic cells into [[Biology:Nucleosome|nucleosome]]s.<ref name=":10" /> [[Biology:Hydrogenosome|Hydrogenosome]]s used in anaerobic activity may have originated in this time from an archaeon.<ref name=":2">{{Cite journal|title = Energy metabolism among eukaryotic anaerobes in light of Proterozoic ocean chemistry|journal = Philosophical Transactions of the Royal Society of London B: Biological Sciences|date = 2008-08-27 |df=dmy-all |issn = 0962-8436|pmc = 2606767|pmid = 18468979|pages = 2717–2729|volume = 363|issue = 1504|doi = 10.1098/rstb.2008.0031|language = en|first1 = Marek|last1 = Mentel|first2 = William|last2 = Martin}}</ref><ref name=":11">{{Cite journal| last1 = Martin| first1 = W.| last2 = Müller| first2 = M.| year=1998 |df=dmy-all| title = The hydrogen hypothesis for the first eukaryote| journal = Nature| volume = 392| issue = 6671| pages = 37–41| doi = 10.1038/32096| issn = 0028-0836| pmid=9510246| bibcode = 1998Natur.392...37M| s2cid = 338885}}</ref>

Given the evolutionary landmarks achieved by eukaryotes, this time period could be considered an important precursor to the Cambrian explosion about 0.54 Ga, and the evolution of relatively large, complex life.<ref name=":10" />

===Ecology===
Due to the marginalization of large food particles, such as algae, in favor of cyanobacteria and prokaryotes which do not transmit as much energy to higher [[Earth:Trophic level|trophic level]]s, a complex [[Biology:Food web|food web]] likely did not form, and large lifeforms with high energy demands could not evolve. Such a food web probably only sustained a small number of [[Biology:Protist|protist]]s as, in a sense, [[Biology:Apex predator|apex predator]]s.<ref name=Gueneli>{{cite journal|first1=N.|last1=Gueneli|first2=A. M.|last2=McKenna|first3=N.|last3=Ohkouchi|first4=C. J.|last4=Boreham|first5=J.|last5=Beghin|first6=E. J.|last6=Javaux|first7=J. J.|last7=Brocks|year=2018|title=1.1-billion-year-old porphyrins establish a marine ecosystem dominated by bacterial primary producers|journal=Proceedings of the National Academy of Sciences|volume=115|issue=30|pages=6978–6986|doi=10.1073/pnas.1803866115|pmid=29987033|pmc=6064987|bibcode=2018PNAS..115E6978G|doi-access=free}}</ref>

The presumably oxygenic photosynthetic eukaryotic [[Biology:Acritarch|acritarch]]s, perhaps a type of microalga, inhabited the Mesoproterozoic surface waters.<ref>{{cite journal|first1=M.|last1=Moczydlowska|first2=E.|last2=Landing|first3=W.|last3=Zang|first4=T.|last4=Palacios|year=2011|title=Proterozoic phytoplankton and timing of Chlorophyte algae origins|journal=Palaeontology|volume=54|issue=4|pages=721–733|doi=10.1111/j.1475-4983.2011.01054.x|bibcode=2011Palgy..54..721M |doi-access=free}}</ref> Their population may have been largely limited by nutrient availability rather than predation because species have been reported to have survived for hundreds of millions of years, but after 1 Ga, species duration dropped to about 100 Ma, perhaps due to increased herbivory by early protists. This is consistent with species survival dropping to 10 Ma just after the Cambrian explosion and the expansion of herbivorous animals.<ref>{{cite journal|first=S. M.|last=Stanley|year=2008|title=Predation defeats competition on the seafloor|journal=Paleobiology|volume=31|issue=1|page=12<!--only citing this page-->|doi=10.1666/07026.1|bibcode=2008Pbio...34....1S |s2cid=83713101}}</ref>

The relatively low concentrations of molybdenum in the ocean throughout the Boring Billion have been suggested as a major limiting factor that kept populations of open ocean nitrogen fixing microorganisms, which require molybdenum to produce [[Biology:Nitrogenase|nitrogenase]]s, low, although freshwater and coastal environments close to riverine sources of dissolved molybdenum may have still hosted significant communities of nitrogen fixers. The low rate of nitrogen fixation, which only ended during the Cryogenian with the evolution of planktonic nitrogen fixers, meant that free ammonium was in short supply across this time interval, severely constraining the evolution and diversification of multicellular biota.<ref>{{cite journal |last1=Sánchez-Baracaldo |first1=Patricia |last2=Ridgwell |first2=Andy |last3=Raven |first3=John A. |date=17 March 2014 |title=A Neoproterozoic Transition in the Marine Nitrogen Cycle |journal=Current Biology |volume=24 |issue=6 |pages=652–657 |doi=10.1016/j.cub.2014.01.041 |pmid=24583016 |s2cid=16756351 |doi-access=free }}</ref>

===Life on land===
Some of the earliest evidence of the prokaryotic colonization of land dates to before 3 Ga,<ref>{{cite journal|last=Homann|first=M.|display-authors=et al.|year=2018|title=Microbial life and biogeochemical cycling on land 3,220 million years ago|journal=Nature Geoscience|volume=11|issue=9|pages=665–671|doi=10.1038/s41561-018-0190-9|bibcode=2018NatGe..11..665H|s2cid=134935568|url=https://hal.univ-brest.fr/hal-01901955/file/Homann%20et%20al.%202018%20-%20accepted-1.pdf}}</ref> possibly as early as 3.5 Ga.<ref>{{cite journal|first1=R. J.|last1=Baumgartner|first2=M. J.|last2=van Kranendonk|display-authors=et al.|title=Nano−porous pyrite and organic matter in 3.5-billion-year-old stromatolites record primordial life|journal=Geology|volume=47|issue=11|pages=1039–1043|year=2019|doi=10.1130/G46365.1|bibcode=2019Geo....47.1039B|s2cid=204258554 |url=https://discovery.ucl.ac.uk/id/eprint/10087275/1/Baumgartner%20et%20al%202019%20accepted.pdf}}</ref> During the Boring Billion, land may have been inhabited mainly by cyanobacterial mats.<ref name=":10" /><ref>{{Cite journal |last1=Watanabe |first1=Yumiko|last2=Martini |first2=Jacques E. J. |last3=Ohmoto |first3=Hiroshi |date=2000-11-30 |df=dmy-all |title=Geochemical evidence for terrestrial ecosystems 2.6 billion years ago |journal=Nature|volume=408 |issue=6812 |pages=574–578 |doi=10.1038/35046052 |issn=0028-0836 |pmid=11117742 |bibcode=2000Natur.408..574W|s2cid=4427507}}</ref><ref name=Horodyski1994>{{Cite journal |last1=Horodyski |first1=R. J. |last2=Knauth |first2=L. P. |year=1994 |df=dmy-all |title=Life on land in the precambrian |journal=Science |volume=263 |issue=5146 |pages=494–498 |doi=10.1126/science.263.5146.494 |issn=0036-8075 |pmid=17754880 |bibcode=1994Sci...263..494H|s2cid=37687767 }}</ref><ref>{{Cite journal |last1=Retallack |first1=Gregory J. |last2=Mindszenty |first2=Andrea |date=1994-04-01 |df=dmy-all |title=Well preserved late Precambrian Paleosols from Northwest Scotland |url=http://jsedres.geoscienceworld.org/content/64/2a/264 |journal=Journal of Sedimentary Research |language=en |volume=64 |issue=2a |pages=264–281 |doi=10.1306/D4267D7A-2B26-11D7-8648000102C1865D |issn=1527-1404}}</ref><ref>{{Cite journal| last1 = Horodyski| first1 = R. J.| last2 = Knauth| first2 = L. P.| year=1994 |df=dmy-all| title = Life on land in the precambrian| journal = Science| volume = 263| issue = 5146| pages = 494–498| doi = 10.1126/science.263.5146.494| issn = 0036-8075| pmid = 17754880| bibcode = 1994Sci...263..494H| s2cid = 37687767}}</ref> Dust would have supplied an abundance of nutrients and a means of dispersal for surface-dwelling microbes, though microbial communities could have also formed in caves and freshwater lakes and rivers.<ref name=Campesi2013/><ref>{{Cite journal |url=https://risweb.st-andrews.ac.uk/portal/da/researchoutput/life-on-land-in-the-proterozoic-evidence-from-the-torridonian-rocks-of-northwest-scotland(b8c702c9-ba95-4ac8-b78c-84293f17881d).html |title=Life on land in the Proterozoic: Evidence from the Torridonian rocks of northwest Scotland |volume=30 |issue=9 |pages=811 |journal=Geology |year=2002 |doi=10.1130/0091-7613(2002)030<0811:LOLITP>2.0.CO;2 |first=Anthony Robert |last=Prave |access-date=2016-03-05 |df=dmy-all |bibcode=2002Geo....30..811P}}</ref> By 1.2 Ga, microbial communities may have been abundant enough to have affected weathering, [[Earth:Erosion|erosion]], sedimentation, and various geochemical cycles,<ref name=Horodyski1994/> and expansive microbial mats could indicate [[Biology:Biological soil crust|biological soil crust]] was abundant.<ref name=Campesi2013>{{cite journal|first=H.|last=Beraldi-Campesi|year=2013|title=Early life on land and the first terrestrial ecosystems|journal=Ecological Processes|volume=2|issue=1|pages=1–17|doi=10.1186/2192-1709-2-1|doi-access=free}}</ref>

The earliest terrestrial eukaryotes may have been lichen fungi about 1.3 Ga,<ref name=Heckman2001>{{cite journal|first1=D. S.|last1=Heckman|first2=D. M.|last2=Geiser|first3=B. R.|last3=Eidell|first4=R. L.|last4=Stauffer|first5=N. L.|last5=Kardos|first6=S. B.|last6=Hedges|year=2001|title=Molecular Evidence for the Early Colonization of Land by Fungi and Plants|journal=Science|volume=293|issue=5532|pages=494–498|doi=10.1126/science.263.5146.494|pmid=17754880|bibcode=1994Sci...263..494H |s2cid=37687767}}</ref> which grazed on the microbial mats.<ref name=Campesi2013/> Abundant eukaryotic microfossils from the freshwater Scottish Torridon Group seems to indicate eukaryotic dominance in non-marine habitats by 1 Ga,<ref>{{cite journal|first1=P. K.|last1=Strother|first2=L.|last2=Battison|first3=M. D.|last3=Brasier|first4=C. H.|last4=Wellman|year=2011|title=Earth's earliest non-marine eukaryotes|journal=Nature|volume=473|issue=7348|pages=505–509|doi=10.1038/nature09943|pmid=21490597|bibcode=2011Natur.473..505S|s2cid=4418860|url=https://www.researchgate.net/publication/51048998}}</ref> probably due to increased nutrient availability in areas closer to the continents and continental runoff.<ref name=Parnell2015/> These lichen may have later facilitated plant colonization 0.75 Ga in some manner.<ref name=Heckman2001/> A massive increase in terrestrial photosynthetic biomass seems to have occurred about 0.85 Ga, indicated by a flux in terrestrially-sourced carbon, which may have increased oxygen levels enough to support an expansion of multicellular eukaryotes.<ref>{{cite journal|first=L. P.|last=Knauth|year=2009|title=The late Precambrian greening of the Earth|journal=Nature|volume=460|issue=7256|pages=728–732|doi=10.1038/nature08213|pmid=19587681|bibcode=2009Natur.460..728K|s2cid=4398942}}</ref>

==See also==
* {{annotated link|Earth:Precambrian}}
* {{annotated link|Earth:Ediacaran biota}}
* {{annotated link|Earth:Francevillian biota}}
* {{annotated link|Earth:Snowball Earth}}
* The [[Physics:Natural nuclear fission reactor|natural nuclear fission reactor]]s at what is now [[Engineering:Oklo|Oklo]], Gabon were active in this era

== External links ==
*[https://uk.style.yahoo.com/earth-boring-billion-years-stagnant-113908067.html Earth’s 'boring billion' years of stagnant, stinking oceans might actually have been rather dynamic]

[[Category:Astrobiology]]

== References ==
{{Reflist}}

[[Category:Proterozoic]]
[[Category:Plate tectonics]]
[[Category:Geological periods]]

{{Sourceattribution|Boring Billion}}