The oldest debated evidence of life
What happened
In the Dresser Formation of the Pilbara Craton in Western Australia, geologists have documented stromatolites, layered mounds built by microbial mats, dated to about 3.48 billion years old, alongside fossilized hot-spring mineral deposits called geyserite. A study in Nature Communications treats this combination, stromatolites plus fractionated carbon and sulfur isotopes plus the geyserite itself, as some of Earth's earliest convincing evidence of life, and the first sign that early life lived on land in hot springs, not only in the sea. A rival, older claim goes further: in 2016 a team led by Allen Nutman reported what they called microbial structures in 3.7-billion-year-old rock at Isua, Greenland, in Nature. Other geologists pushed back hard. Abigail Allwood's team re-examined the Isua structures and argued they were lined up too neatly, like children's toes in a row, and lacked the internal layering real stromatolites should have, favoring a non-biological origin from rock deformation instead.
Why it matters
Whichever claim holds up, the dispute itself is the lesson: the further back you push the search for life, the harder it becomes to tell a genuine biological signature from a rock formation that merely looks like one. Nutman has said he expects the Isua question to stay unresolved for another five to ten years, which is itself a fair measure of how difficult this evidence is to read.
How we know
The Pilbara case rests on multiple independent signals agreeing: stromatolite shape, isotope ratios consistent with biology, and preserved hot-spring minerals. The Isua case rests on the shape and arrangement of small ridges in metamorphosed rock, which is exactly what critics dispute, arguing the same shapes can form from squeezing and heating rock with no life involved at all.
Sources
- Djokic et al.. Earliest signs of life on land preserved in ca. 3.5 Ga hot spring deposits (2017) · Peer-reviewed (author-declared)pmc.ncbi.nlm.nih.gov · Cited as a "journal" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
- NASA Astrobiology. On the Ground in Greenland · Reputable sourceastrobiology.nasa.gov · The domain "astrobiology.nasa.gov" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- Nutman et al.. Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures (2016) · Peer-reviewed (author-declared)doi.org · Cited as a "journal" source (no stronger domain match).
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