Editing Archean (section)

==Etymology and changes in classification==
The word ''Archean'' is derived from the Greek word {{lang|grc-Latn|arkhē}} ({{wikt-lang|grc|ἀρχή}}), meaning 'beginning, origin'.<ref>{{OEtymD|Archaean}}</ref> The [[Pre-Cambrian]] had been believed to be without life (azoic); however, fossils were found in deposits that were judged to belong to the [[Azoic age]]. Before the Hadean Eon was recognized, the Archean spanned Earth's early history from its formation about 4,540&nbsp;million years ago until 2,500&nbsp;million years ago.

Instead of being based on [[stratigraphy]], the beginning and end of the Archean Eon are defined [[Chronometric dating|chronometrically]]. The eon's lower boundary or starting point of 4,031±3&nbsp;million years ago is officially recognized by the [[International Commission on Stratigraphy]],<ref name="GSSP Web" /> which is the age of the oldest known intact rock formations on Earth. Evidence of rocks from the preceding Hadean Eon are therefore restricted by definition to non-rock and non-terrestrial sources such as individual mineral grains and lunar samples.