The other day, I posted some thoughts regarding a 2017 article proposing evidence of terrestrial life between 3.77 and 4.28 billion years ago:
“An amazing thought: “New find could be oldest evidence of life ever discovered””
I thought this astoundingly early, given the fact that the Earth itself isn’t much older than that.
Here’s another article suggesting that life may have commenced on our planet at a remarkably early time:
“Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon”
“To our knowledge,” say the four authors of the article (three from the Department of Earth, Planetary, and Space Sciences at the University of California at Los Angeles, and one from Stanford University’s School of Earth, Energy, and Environmental Sciences), “we report here the first unambiguous carbon isotopic measurements of terrestrial Hadean material.” What they have identified, they think, “may be evidence for the origin of life on Earth by 4.1 Ga.”
[In the article and its abstract, the abbreviations Ga and My refer, respectively, to a “giga-annum” (or a billion years) and to “a million years.”]
The abstract of the article reads as follows:
Evidence of life on Earth is manifestly preserved in the rock record. However, the microfossil record only extends to ∼3.5 billion years (Ga), the chemofossil record arguably to ∼3.8 Ga, and the rock record to 4.0 Ga. Detrital zircons from Jack Hills, Western Australia range in age up to nearly 4.4 Ga. From a population of over 10,000 Jack Hills zircons, we identified one >3.8-Ga zircon that contains primary graphite inclusions. Here, we report carbon isotopic measurements on these inclusions in a concordant, 4.10 ± 0.01-Ga zircon. We interpret these inclusions as primary due to their enclosure in a crack-free host as shown by transmission X-ray microscopy and their crystal habit. Their δ13CPDB of −24 ± 5‰ is consistent with a biogenic origin and may be evidence that a terrestrial biosphere had emerged by 4.1 Ga, or ∼300 My earlier than has been previously proposed.
And here is their concluding paragraph:
This study extends the terrestrial carbon isotope record ∼300 My beyond the previously oldest-measured samples from southwest Greenland. Our interpretation that the light C isotope signature in primary graphitic inclusions could reflect biologic processes is consistent with an estimate from molecular divergence in prokaryote phylogenetic relationships that a terrestrial biosphere had emerged by 4.1 Ga. Confirming such a connection would represent a potentially transformational scientific advance. However, given the low occurrence of carbon-bearing Hadean zircons, establishing a Hadean carbon cycle and its possible bearing on the origin of life will require enormous and sustained efforts.
Once again, it seems that life may have appeared on the Earth at the earliest time that it possibly could. That’s an arresting fact.
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