~3.7 billion years agoPeer-reviewedDebated
Earliest life on Earth
On the timeline · around ~3.7 billion years ago · Geologic
What happened
Microbial life — or its chemical and structural traces — appears; among the oldest evidence are stromatolite-like structures in Greenland's Isua rocks.
Why it matters
The beginning of life, the root of the entire tree of living things.
How we know
Putative stromatolites and carbon-isotope signatures in ~3.7-billion-year-old rocks; the exact timing remains debated.
The earliest biosignatures are contested among researchers.