Life › Origin of life › Origin of life
Earliest claimed traces of life
3.7–4.1 billion years old (Greenland, Canada, Australia; all debated)· Fossil or site· Microbes & cells
DebatedScientists disagree about when, how or why.
Disputed chemical and physical traces in rocks 3.7–4.1 billion years old that may be the earliest signs of life.
See it on the Life map →What happened
The candidates: carbon specks inside a 4.1-billion-year-old zircon from Jack Hills, Australia (2015); carbon-rich graphite and cone shapes in 3.7-billion-year-old rocks at Isua, Greenland (1996–2016); and tiny iron-rich tubes from Nuvvuagittuq, Quebec, dated anywhere from 3.77 to 4.28 billion years (2017). Several rely on carbon isotopes, since life prefers lighter carbon-12. But non-living chemistry can mimic these signals, and all these rocks have been heated and squeezed.
Why it matters
If any is real, life began very soon after Earth had oceans, hinting that it starts easily; if none is, the firm record begins about 3.5 billion years ago.
The evidence (fossils, genes, rocks)
Carbon isotope ratios, microscope and 3-D imaging of the structures, and radioactive dating of the host rocks; every claim has drawn published rebuttals.
Still debated
Whether any claim is truly biological, and, for Nuvvuagittuq, how old the rocks really are.
Connections (2)
▸Earliest claimed traces of life would push back the date of Origin of lifeDebated
The connection
If carbon traces in 4.1-billion-year-old crystals or 3.7-billion-year-old Greenland rocks were made by life, life began within a few hundred million years of Earth having oceans. That would suggest life starts readily when conditions allow. If the claims fail, the firm record starts about 3.5 billion years ago.
When and how
Isua, Greenland, claims from 1996 to 2016; Jack Hills zircon carbon, Western Australia, reported by Elizabeth Bell and colleagues at UCLA in 2015; Nuvvuagittuq, Quebec, 2017.
How sure are we?
Each claim rests on light carbon (life prefers carbon-12) or on shapes; both can form without life, so none is fully accepted.
Debates and open questions
Whether such heated, squeezed rocks can ever settle the date; molecular-clock estimates placing LUCA near 4.2 billion years ago suggest life is older than any firm trace.
▸Earliest claimed traces of life would predate StromatolitesDebated
The connection
The oldest widely accepted stromatolites are 3.48 billion years old, in Australia. In 2016 a team reported 3.7-billion-year-old cone-shaped stromatolites at Isua, Greenland, which would beat them by about 220 million years. A 2018 re-examination argued the cones are squeezed rock, not microbial structures.
When and how
Allen Nutman and colleagues announced the Isua find in 2016; Abigail Allwood and colleagues challenged it in 2018.
How sure are we?
The challenge used 3-D views and chemistry showing the shapes formed by deformation. Most geologists now doubt the Isua stromatolites.
Debates and open questions
Whether any true stromatolites survive in Earth's few rocks of that age, almost all of which have been heated and squashed.