Definition of Archean in US English:


(British Archaean)


  • 1Relating to or denoting the eon that constitutes the earlier (or middle) part of the Precambrian, in which there was no life on earth. It precedes the Proterozoic eon.

    The Archean extended from the origin of the earth (see Precambrian) to about 2,500 million years ago. In models that include the Priscoan eon, the Archean began about 4,000 million years ago

    Also called "the Azoic"
    • ‘The geological history of Archaean greenstone belts is controversial and, to date, no tectonic model for their evolution has been agreed upon.’
    • ‘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.’
    • ‘Comparison of the ‘bar code’ from the approximately 35 different Archean continental fragments (at least eight of which are in Canada) represents a key tool for proposing reconstructions between these fragments.’
    • ‘The contacts between the complex and the Archaean metamorphic rocks are intrusive.’
    • ‘However, most Archean volcanic rocks occur as deformed and fault-fragmented packages termed greenstone belts.’
    1. 1.1as noun the Archean The Archean eon or the system of rocks deposited during it.


Late 19th century: from Greek arkhaios ‘ancient’ + -an.