Editing Hadean (section)

==Atmosphere==
A sizable quantity of water would have been in the material that formed Earth.<ref name=Drake>{{cite journal |last=Drake |first=Michael J. |date=April 2005 |title=Origin of water in the terrestrial planets |journal=Meteoritics & Planetary Science |bibcode=2005M&PS...40..515J |doi=10.1111/j.1945-5100.2005.tb00960.x |doi-access=free |volume=40 |number=4 |pages=519–527}}</ref> Water molecules would have escaped Earth's gravity more easily when the planet was less massive during its formation. [[Photodissociation]] by short-wave [[ultraviolet]] in [[sunlight]] could [[water splitting|split]] [[surface water]] molecules into [[oxygen]] and [[hydrogen]], the former of which would readily react to form compounds in the then-[[reducing atmosphere]], while the latter (along with the similarly light [[helium]]) would be expected to continually leave the atmosphere (as it does to the present day) due to [[atmospheric escape]].

Part of the ancient planet is theorized to have been disrupted by the [[giant impact hypothesis|impact that created the Moon]], which should have caused the melting of one or two large regions of Earth. Earth's present composition suggests that there was not complete remelting as it is difficult to completely melt and mix huge rock masses.<ref>{{cite web |last=Taylor |first=G. Jeffrey |title=Origin of the Earth and Moon |website=Solar System Exploration |publisher=NASA |url=http://solarsystem.nasa.gov/scitech/display.cfm?ST_ID=446 |url-status=dead |archive-url=https://web.archive.org/web/20150308165917/http://solarsystem.nasa.gov/scitech/display.cfm?ST_ID=446 |archive-date=March 8, 2015}}</ref> However, a fair fraction of material should have been vaporized by this impact. The material would have condensed within 2,000 years.<ref name=Sleep2001>{{cite journal |last1=Sleep |first1=NH |last2=Zahnle |first2=K |last3=Neuhoff |first3=PS |year=2001 |title=Initiation of clement surface conditions on the earliest Earth |journal=[[Proceedings of the National Academy of Sciences|PNAS]] |doi=10.1073/pnas.071045698 |doi-access=free |pmid=11259665 |pmc=31109 |bibcode=2001PNAS...98.3666S |volume=98 |issue=7 |pages=3666–3672}}</ref> The initial [[magma ocean]] solidified within 5 million years,<ref>{{cite journal|first=LT|last=Elkins-Tanton|title=Linked magma ocean solidification and atmospheric growth for Earth and Mars|journal=Earth and Planetary Science Letters|volume=271|issue=1–4|year=2008|pages=181–191|doi=10.1016/j.epsl.2008.03.062|bibcode=2008E&PSL.271..181E }}</ref> leaving behind hot volatiles which probably resulted in a heavy {{chem|link=carbon dioxide|CO|2}} atmosphere with [[hydrogen]] and [[water vapor]]. The initial heavy atmosphere had a surface temperature of {{cvt|230|C|F}} and an [[atmospheric pressure]] of above 27 [[standard atmosphere (unit)|standard atmosphere]]s.<ref name=Sleep2001/>