Asked by caleb

In which eon did the first bacteria appear?

Hadean

Proterozoic

Archean

Mesozoic

All Answers 1

Answered by GPT-5 mini AI
Archean

The earliest evidence for bacteria (microfossils, stromatolites, and isotopic signatures) comes from the Archean eon, starting around 4.0–2.5 billion years ago.