Earth Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.Anti-spam check. Do not fill this in! === Origin of life and evolution === {{Main|Abiogenesis{{!}}Origin of life|Earliest known life forms|History of life}} [[Chemical reaction]]s led to the first self-replicating molecules about four billion years ago. A half billion years later, the [[last universal common ancestor|last common ancestor of all current life]] arose.<ref name="sa282_6_90" /> The evolution of [[photosynthesis]] allowed the Sun's energy to be harvested directly by life forms. The resultant [[molecular oxygen]] ({{chem2|O2}}) accumulated in the atmosphere and due to interaction with ultraviolet solar radiation, formed a protective [[ozone layer]] ({{chem2|O3}}) in the upper atmosphere.<ref name="NYT-20131003">{{cite news |last=Zimmer |first=Carl |author-link=Carl Zimmer |title=Earth's Oxygen: A Mystery Easy to Take for Granted |url=https://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html |archive-url=https://web.archive.org/web/20131003121909/http://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html |archive-date=3 October 2013 |url-access=limited |date=3 October 2013 |work=[[The New York Times]] |access-date=3 October 2013}}</ref> The incorporation of smaller cells within larger ones resulted in the [[endosymbiotic theory|development of complex cells]] called [[eukaryote]]s.<ref name="jas22_3_225" /> True multicellular organisms formed as cells within [[Colony (biology)|colonies]] became increasingly specialized. Aided by the absorption of harmful [[ultraviolet radiation]] by the ozone layer, life colonized Earth's surface.<ref name="burton20021129" /> Among the earliest [[fossil]] evidence for life is [[microbial mat]] fossils found in 3.48 billion-year-old [[sandstone]] in [[Western Australia]],<ref>{{cite journal |last1=Noffke |first1=Nora |author-link=Nora Noffke |last2=Christian |first2=Daniel |last3=Wacey |first3=David |last4=Hazen |first4=Robert M. |author4-link=Robert Hazen |title=Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia |date=8 November 2013 |journal=[[Astrobiology (journal)|Astrobiology]] |doi=10.1089/ast.2013.1030 |bibcode=2013AsBio..13.1103N |pmid=24205812 |pmc=3870916 |volume=13 |issue=12 |pages=1103–1124}}</ref> [[Biogenic substance|biogenic]] [[graphite]] found in 3.7 billion-year-old [[metasediment]]ary rocks in [[Western Greenland]],<ref>{{cite journal |last1=Ohtomo |first1=Yoko |last2=Kakegawa |first2=Takeshi |last3=Ishida |first3=Akizumi |last4=Nagase |first4=Toshiro |last5=Rosing |first5=Minik T. |s2cid=54767854 |display-authors=3 |date=January 2014 |title=Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks |journal=[[Nature Geoscience]] |volume=7 |issue=1 |pages=25–28 |bibcode=2014NatGe...7...25O |doi=10.1038/ngeo2025 |issn=1752-0894}}</ref> and remains of [[biotic material]] found in 4.1 billion-year-old rocks in Western Australia.<ref>{{cite news |last=Borenstein |first=Seth |title=Hints of life on what was thought to be desolate early Earth |url=http://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html |date=19 October 2015 |work=[[Excite (web portal)|Excite]] |location=Yonkers, NY |publisher=[[Mindspark Interactive Network]] |agency=[[Associated Press]] |access-date=20 October 2015 |archive-url=https://web.archive.org/web/20160818063111/https://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html |archive-date=18 August 2016}}</ref><ref>{{cite journal |last1=Bell |first1=Elizabeth A. |last2=Boehnike |first2=Patrick |last3=Harrison |first3=T. Mark |author-link3=T. Mark Harrison |last4=Mao |first4=Wendy L. |author4-link=Wendy Mao |date=19 October 2015 |title=Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon |journal=Proc. Natl. Acad. Sci. U.S.A. |doi=10.1073/pnas.1517557112 |issn=1091-6490 |pmid=26483481 |pmc=4664351 |volume=112 |issue=47 |pages=14518–4521 |bibcode=2015PNAS..11214518B |doi-access=free}} Early edition, published online before print.</ref> The [[Earliest known life forms|earliest direct evidence of life]] on Earth is contained in 3.45 billion-year-old [[Australia (continent)|Australian]] rocks showing fossils of [[microorganism]]s.<ref>{{cite web |last=Tyrell |first=Kelly April |title=Oldest fossils ever found show life on Earth began before 3.5 billion years ago |url=https://news.wisc.edu/oldest-fossils-ever-found-show-life-on-earth-began-before-3-5-billion-years-ago/ |date=18 December 2017 |publisher=[[University of Wisconsin–Madison]] |access-date=18 December 2017}}</ref><ref>{{cite journal |last1=Schopf |first1=J. William |last2=Kitajima |first2=Kouki |last3=Spicuzza |first3=Michael J. |last4=Kudryavtsev |first4=Anatolly B. |last5=Valley |first5=John W. |title=SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions |year=2017 |journal=[[Proceedings of the National Academy of Sciences of the United States of America|PNAS]] |volume=115 |issue=1 |pages=53–58 |doi=10.1073/pnas.1718063115 |pmid=29255053 |pmc=5776830 |bibcode=2018PNAS..115...53S |doi-access=free}}</ref>[[File:Archean.png|thumb|An artist's impression of the [[Archean]], the [[Geologic time scale#Divisions of geologic time|eon]] after Earth's formation, featuring round [[stromatolite]]s, which are early oxygen-producing forms of life from billions of years ago. After the [[Late Heavy Bombardment]], [[Earth's crust]] had cooled, its water-rich barren [[planetary surface|surface]] is marked by [[continent]]s and [[volcano]]es, with the Moon still orbiting Earth half as far as it is today, appearing 2.8 times larger and producing strong [[tide]]s.<ref name="Lunar and Planetary Institute">{{cite web |title=Earth-Moon Dynamics |url=https://www.lpi.usra.edu/exploration/training/illustrations/earthMoon/ |access-date=2 September 2022 |website=Lunar and Planetary Institute}}</ref>|center|500x500px]]During the [[Neoproterozoic]], {{val|1000|to|539|u=Ma}}, much of Earth might have been covered in ice. This hypothesis has been termed "[[Snowball Earth]]", and it is of particular interest because it preceded the [[Cambrian explosion]], when multicellular life forms significantly increased in complexity.<ref>{{cite book|page=42|title=Climate Change and the Course of Global History|last1=Brooke|first1=John L.|year= 2014|publisher=Cambridge University Press|isbn=978-0-521-87164-8}}</ref><ref>{{cite book|page=56|title=Epigenetic Mechanisms of the Cambrian Explosion|last1=Cabej|first1=Nelson R.|year=2019|publisher=Elsevier Science|isbn=978-0-12-814312-4}}</ref> Following the Cambrian explosion, {{val|535|u=Ma}}, there have been at least five major [[Extinction event|mass extinctions]] and many minor ones.<ref name="Stanley_2016" /> Apart from the proposed current [[Holocene extinction]] event, the [[Cretaceous–Paleogene extinction event|most recent]] was {{val|66|u=Ma}}, when [[Chicxulub impactor|an asteroid impact]] triggered the extinction of non-avian dinosaurs and other large reptiles, but largely spared small animals such as insects, [[mammal]]s, lizards and birds. Mammalian life has diversified over the past {{val|66|u=Mys}}, and several million years ago, an African [[ape]] species gained the ability to stand upright.<ref name="gould1994" /><ref>{{Cite journal |last=Daver |first=G. |last2=Guy |first2=F. |last3=Mackaye |first3=H. T. |last4=Likius |first4=A. |last5=Boisserie |first5=J.-R. |last6=Moussa |first6=A. |last7=Pallas |first7=L. |last8=Vignaud |first8=P. |last9=Clarisse |first9=N. D. |date=2022 |title=Postcranial evidence of late Miocene hominin bipedalism in Chad |url=https://www.nature.com/articles/s41586-022-04901-z |journal=Nature |language=en |volume=609 |issue=7925 |pages=94–100 |doi=10.1038/s41586-022-04901-z |issn=1476-4687}}</ref> This facilitated tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, which led to the [[Human evolution|evolution of humans]]. The [[History of agriculture|development of agriculture]], and then [[List of ancient civilizations|civilization]], led to humans having an [[Human impact on the environment|influence on Earth]] and the nature and quantity of other life forms that continues to this day.<ref name="bgsa119_1_140" /> Summary: Please note that all contributions to Christianpedia may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here. You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see Christianpedia:Copyrights for details). Do not submit copyrighted work without permission! Cancel Editing help (opens in new window) Discuss this page