Editing Geology (section)

==Geological time==
{{Main|Geological history of Earth|Geologic time scale}}

The geological time scale encompasses the history of the Earth.<ref>[http://www.stratigraphy.org/ International Commission on Stratigraphy]. {{webarchive|url=https://web.archive.org/web/20050920105136/http://www.stratigraphy.org/|date=September 20, 2005}}. stratigraphy.org.</ref> It is bracketed at the earliest by the dates of the first [[Solar System]] material at 4.567 [[Gigaannum|Ga]]<ref name="4.567">{{Cite journal | doi = 10.1126/science.1073950| title = Lead Isotopic Ages of Chondrules and Calcium-Aluminum-Rich Inclusions| journal = Science| volume = 297| issue = 5587| pages = 1678–1683| year = 2002| last1 = Amelin | first1 = Y.|bibcode = 2002Sci...297.1678A| pmid=12215641| s2cid = 24923770}}</ref> (or 4.567 billion years ago) and the formation of the Earth at
4.54 Ga<ref name="4.54">{{cite journal|author=Patterson, C.|year= 1956|title=Age of Meteorites and the Earth|journal= Geochimica et Cosmochimica Acta |volume=10|issue= 4|pages= 230–237|bibcode = 1956GeCoA..10..230P |doi = 10.1016/0016-7037(56)90036-9 }}</ref><ref name="4.54 book">{{Cite book |author=Dalrymple |first=G. Brent |title=The age of the earth |publisher=Stanford University Press |year=1994 |isbn=978-0-8047-2331-2 |location=Stanford, California}}</ref>
(4.54 billion years), which is the beginning of the [[Hadean eon]]{{snd}}a division of geological time. At the later end of the scale, it is marked by the present day (in the [[Holocene epoch]]).

===Timescale of the Earth===

{{Timeline Geological Timescale}}

===Important milestones on Earth===
[[File:Geologic Clock with events and periods.svg|thumb|upright=1.35|Geological time in a diagram called a [[geological clock]], showing the relative lengths of the [[geologic eon|eon]]s and [[era (geology)|era]]s of the Earth's history]]
* 4.567 [[Ga (unit)|Ga]] (gigaannum: billion years ago): [[Solar system formation]]<ref name="4.567" />
* 4.54 Ga: [[Accretion (astrophysics)|Accretion, or formation]], of Earth<ref name="4.54" /><ref name="4.54 book" />
* c. 4 Ga: End of [[Late Heavy Bombardment]], the first life
* c. 3.5 Ga: Start of [[photosynthesis]]
* c. 2.3 Ga: Oxygenated [[atmosphere]], first [[snowball Earth]]
* 730–635 [[Ma (unit)|Ma]] (megaannum: million years ago): second snowball Earth
* 541 ± 0.3 Ma: [[Cambrian explosion]] – vast multiplication of hard-bodied life; first abundant [[fossil]]s; start of the [[Paleozoic]]
* c. 380 Ma: First [[vertebrate]] land animals
* 250 Ma: [[Permian-Triassic extinction]] – 90% of all land animals die; end of Paleozoic and beginning of [[Mesozoic]]
* 66 Ma: [[Cretaceous–Paleogene extinction]] – [[Dinosaur]]s die; end of Mesozoic and beginning of [[Cenozoic]]
* c. 7 Ma: First [[hominin]]s appear
* 3.9 Ma: First [[Australopithecus]], direct ancestor to modern [[Homo sapiens]], appear
* 200 [[Ma (unit)|ka]] (kiloannum: thousand years ago): First modern Homo sapiens appear in East Africa

===Timescale of the Moon===
{{main|Lunar geologic timescale}}
{{Timeline Lunar Geological Timescale}}

===Timescale of Mars===
{{main|Geological history of Mars}}
{{Mars timescale}}