Life on Earth likely started 4.1 billion years ago—much earlier than scientists thought
UCLA geochemists have found evidence that life likely existed on Earth at least 4.1 billion years ago—300 million years earlier than previous research suggested. The discovery indicates that life may have begun shortly after the planet formed 4.54 billion years ago.
“Twenty years ago, this would have been heretical; finding evidence of life 3.8 billion years ago was shocking,” said Mark Harrison, co-author of the research and a professor of geochemistry at UCLA.
“The early Earth certainly wasn’t a hellish, dry, boiling planet; we see absolutely no evidence for that,” Harrison said. “The planet was probably much more like it is today than previously thought.”
Analyzing 10,000 zircons,
The scientists identified 656 zircons containing dark specks that could be revealing and closely analyzed 79 of them with Raman spectroscopy, a technique that shows the molecular and chemical structure of ancient microorganisms in three dimensions. More.
Obviously, if this find holds up—given the information load even “simple life forms require—we can rule out a strict Darwinian explanation. After all, if such an explanation were correct, rocks would be evolving into life all around us. To say nothing of Boltzmann brains. 😉
That said, sometimes these finds fall apart. Consider the case of the Australian chert find: World’s oldest “microfossils” [3.46 bya] are not life forms after all. Researchers working in the abyss of time are working with fragments. So stay tuned.
Does nature just “naturally” produce life?
Can we solve the mystery of the origin of life by creating life in the lab? (It may come to that.)
With Enceladus the toast of the solar system, here’s a wrap-up of the origin-of-life problem
Anyway, significance and abstract:
Evidence for carbon cycling or biologic activity can be derived from carbon isotopes, because a high 12C/13C ratio is characteristic of biogenic carbon due to the large isotopic fractionation associated with enzymatic carbon fixation. The earliest materials measured for carbon isotopes at 3.8 Ga are isotopically light, and thus potentially biogenic. Because Earth’s known rock record extends only to ~4 Ga, earlier periods of history are accessible only through mineral grains deposited in later sediments. We report 12C/13C of graphite preserved in 4.1-Ga zircon. Its complete encasement in crack-free, undisturbed zircon demonstrates that it is not contamination from more recent geologic processes. Its 12C-rich isotopic signature may be evidence for the origin of life on Earth by 4.1 Ga.
Abstract: 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 d13CPDB 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. (Public access .pdf) – Elizabeth A. Bella, Patrick Boehnke, T. Mark Harrison, and Wendy L. Mao
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