LIFE

The Oldest Traces of Life

~3.7 billion years ago (claims 3.95–3.5 Ga)

Archean · Eoarchean

At this depth of time, life leaves only two kinds of trace: structures built by mats of microbes, and carbon that has been through a living cell and come out measurably lighter than carbon that never went in. Both traces are claimed in rocks from Greenland and Labrador more than 3.7 billion years old. The earliest case most researchers accept is younger: Australian rocks, 3.5 billion years old, where microbial structures lie alongside organic matter sealed inside pyrite.

Why it matters

Life appears within the planet's first billion years, almost as soon as the oceans had settled. If that early date holds, simple life may be no accident but the ordinary outcome on a wet, rocky world.

Dating & uncertaintyDisputed

The oldest claims are contested because both kinds of evidence can be produced without life: circulating hot water alone can stack minerals into layers, and some inorganic reactions sort carbon isotopes exactly as cells do. The doubt narrows as the rocks get younger, and by 3.5 billion years most specialists are persuaded.

Sources

1. Nutman et al. (2016), Nature · Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures
2. Tashiro et al. (2017), Nature · Early trace of life from 3.95 Ga sedimentary rocks in Labrador, Canada
3. Baumgartner et al. (2019), Geology · Nano-porous pyrite and organic matter in 3.5-billion-year-old stromatolites record primordial life
4. Pearce et al. (2018), Astrobiology · Constraining the time interval for the origin of life on Earth

Earth history as one day

04:26:2519 h 34 min before midnight

if Earth’s 4.54 billion years were compressed into a single day