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Sciences : Life existed on Earth 300 millions years earlier than previously thought

Lithified stromatolites on the shores of Lake Thetis, Western Australia. Archean stromatolites are the first direct fossil traces of life on Earth

Scientists believe that life may have existed 300 million years earlier on Earth than previously thought. They analyzed data from tiny pieces of a mineral in Australia and managed to date them back to when the planet was just 400 million years old.

A 580 million year old fossil of Spriggina floundensi, an animal from the Ediacaran period. Such life forms could have been ancestors to the many new forms that originated in the Cambrian Explosion

The researchers were looking at pieces of the mineral zircon, in Western Australia. After taking the samples back to the lab, they found a "chemo-fossil" or a certain mix of carbon isotopes, a study in the journal Proceedings of the National Academy of Sciences stated. Think of it as "the gooey remains of biotic life or anything more complicated", said study co-author Mark Harrison, a UCLA geochemistry professor, as cited by AP. They were able to determine this because carbon has different weights. The carbon residue in the pieces of zircon had a greater percentage of lighter carbon, which scientists usually manage to find in remnants of life, just as if your finger decayed, Harrison said.

Mark Harrison

It is widely accepted that Earth formed around 4.5 billion years ago. However for the first few hundred million years, its surface was believed to be too hot due to molten lava, while there was a lack of water, which would have made it impossible for life to take hold. Life was thought to have appeared around 700 million years after the formation. However Harrison disputes this, saying that there is no physical evidence for the theory. What the zircon shows is "the Earth by 4.1, 4.2 billion years ago was basically behaving like it is today". "This is what transformative science is all about", said Stephen Mojzsis, a University of Colorado scientist, according to AP. "If life is responsible for these signatures, it arrives fast and early". Harrison’s findings were supported by S. Blair Hedges from Temple University, who said they “make sense”. "If life arose relatively quickly on Earth, then it could be common in the universe", he said.

Stephen Blair Hedges

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éditeur : Frank Brunner | ouverture : 11 novembre 2000 | reproduction autorisée en citant la source