Main definitions of archaean in English

: archaean1Archaean2


(also archaeal)

adjective & noun

  • See archaea

    • ‘The conditions at Champagne Pool are ideal for thermophilic, mildly acidophilic archaeans such as the Sulfobales and Thermoproteales.’
    • ‘Each pool has slightly different mineral content, temperature, salinity, etc., so different pools may contain different communities of archaeans and other microbes.’
    • ‘Like bacteria, archaeans have no internal membranes and their DNA exists as a single loop called a plasmid.’
    • ‘In fact, there are fossil microbes known from throughout the Precambrian, but here a second problem surfaces - how do you distinguish fossil archaeans from fossil bacteria?’
    • ‘These pictures show an immense bloom of a halophilic (‘salt-loving’) archaean species, in a saline pond at a salt works near San Quintin, Mexico.’

Main definitions of archaean in English

: archaean1Archaean2


(US Archean)


  • 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 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.’
    • ‘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 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.’
    1. 1.1as noun the Archaean The Archaean aeon or the system of rocks deposited during it.

The Archaean extended from the origin of the earth (see Precambrian) to about 2,500 million years ago. In schemes which include the Priscoan aeon, the Archaean began about 4,000 million years ago


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