archean
/ɑːrˈkiːən/
adjective
- Relating to the earliest geological eon, from about 4 billion to 2.5 billion years ago, when the Earth's crust formed and the first life appeared.
- Scientists study Archean fossils to understand early life.
- Archean rocks are among the oldest found on Earth.
- The Archean eon lasted for nearly 1.5 billion years.