Evidence of life on Earth 4.1 billion years ago has been discovered in Western Australia, pushing back estimates of when living organisms first emerged back 300 million years. They said it is “consistent with a biogenic origin” and that this could be “evidence that a terrestrial biosphere had emerged” 4.1 billion years ago – or around 300 million years earlier than previously suggested.
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S. Blair Hedges of Temple University, who also wasn’t part of the study, said Harrison’s findings makes sense and the accelerated timeline of life fits with his genetic tracking work.
For their study the research team, led by doctoral researcher Elizabeth Bell, looked at about 10,000 zircon crystals that formed out of molten magma being deposited in Australia.
“The early Earth certainly wasn’t a hellish, dry, boiling planet; we see absolutely no evidence for that”, Harrison said.
The results, which have been published in the Proceedings of the National Academy of Sciences, will need to be verified.
The carbon isotopes in the zircon studied suggest “the Earth by 4.1, 4.2 billion years ago was basically behaving like it is today”, Harrison emphasized.
The research was based on a study of thousands of zircons – heavy, durable minerals that scientists said can act as miniature time capsules by capturing and preserving their immediate environment.
“If all life on Earth died during this bombardment, which a few scientists have argued, then life must have restarted quickly”, says study co-author and graduate student Patrick Boehnke, working in Harrison’s lab. It was “much more like it is today than previously thought”, the scientists said.
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. The rock itself and the carbon in the rock were dated to an age of 4.1 billion years using uranium-lead dating methods.
But Harrison says there is little evidence to support that view.
“There is no better case of a primary inclusion in a mineral ever documented, and nobody has offered a plausible alternative explanation for graphite of non-biological origin into a zircon”, he said. The carbon detected in the zircon indicates the presence of photosynthetic life, researchers said.
The carbon signature in the zircon-a specific ratio of the isotopes carbon-12 to carbon-13-is characteristic of life capable of photosynthesis.
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The discovery throws our understanding of the earth’s early years into confusion – it was thought that the planet was so dry and desolate during that time that life would have been impossible.
