Archaean

Part of speech: noun, adjective

Definitions

1. Relating to the earliest geological eon of Earth's history, spanning roughly four to two and a half billion years ago before oxygen built up in the atmosphere
2. Describing the oldest period of the planet's rock record, the eon that preceded the Proterozoic and came before complex life appeared
3. Of or belonging to the geological eon that lasted from about four billion to two and a half billion years ago, when the earliest rocks formed

Etymology: The word "Archaean" is the spelling used for the earliest eon of Earth's history, and it is built from the Greek "archaios", meaning "ancient" or "primeval", with the adjective-forming "-an" added on. The Greek root "archē" lies behind it too, meaning "beginning" or "origin", which is why the same element turns up in words such as "archive" and "archetype". The eon takes its name from the Greek rather than from any place or person. Geologists chose it to mark rocks older than the fossil-bearing strata that the earlier naming of Earth's history had already recognised, so the name simply describes the oldest part of the record. The spelling "Archaean" with the "ae" follows the Greek and is the usual form in British English, while American writers often use "Archean". Both are accepted variants of the same term.

Synonyms: Precambrian

Antonyms: Phanerozoic