1Relating to or denoting the aeon that constitutes the earlier (or middle) part of the Precambrian, in which there was no life on the earth. It precedes the Proterozoic aeon and (in some schemes) is preceded by the Priscoan aeon. Also called the Azoic.
- The answers to questions about early life on Earth are preserved in the oldest rocks, and Canadian earth scientists include some of the world's best Archean geologists and laboratories equipped to study Archean rocks.
- The geological history of Archaean greenstone belts is controversial and, to date, no tectonic model for their evolution has been agreed upon.
- The contacts between the complex and the Archaean metamorphic rocks are intrusive.
Late 19th century: from Greek arkhaios 'ancient' + -an.
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