Editing Geology (section)

===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