Privileged Planet: earliest land (Introduction)

by David Turell , Monday, April 26, 2021, 19:38 (1308 days ago) @ David Turell

Probably before we had thought:

https://www.newscientist.com/article/2275696-earths-land-may-have-formed-500-million-ye...

"Earth’s continental crust may have emerged 500 million years earlier than scientists had previously estimated. Pinning down when our planet’s land emerged could help us understand the conditions in which primitive life began.

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"The big question is: when did continental crusts start forming?

"To try to answer that, Desiree Roerdink at the University of Bergen in Norway and her colleagues analysed 30 ancient rock samples from six sites in Australia, South Africa and India. These contained barite, which can form in hydrothermal vents – fissures in the ocean floor where warm, mineral-rich waters react with seawater.

“'Barites don’t really change, their chemistry contains a fingerprint of the environment in which they formed,” says Roerdink, who presented this work at a meeting of the European Geosciences Union on 26 April.

"She and her team used the ratios of strontium isotopes in the deposits to infer when weathered continental rock began entering the oceans. They found that the weathering began about 3.7 billion years ago.

"When Earth formed 4.5 billion years ago, it was a hellish landscape of molten rock. Eventually, the planet’s outer layer cooled enough to start forming a solid crust covered by a global ocean.

"That kicked off a new geological aeon around 4 billion years ago, known as the Archaean, which is when scientists believe life first emerged. There is strong evidence for microbial activity at least 3.5 billion years ago, but precisely when and how life began is far from clear."

Comment: That puts real land at 3.7 billion years ago with life shortly after. Not much time for chance appearance of something so complex.