Building enough oxygen in our Earth's atmosphere and oceans to become a life-sustaining planet was no quick and easy feat. But it started much earlier than previously thought, and popped up by turns over about 100 million years, as researchers recently found in a paper published in the journal Nature Communications.
The study was done by scientists from the University of Washington and others led by University College London. They surmise that this changes what was earlier thought--that animals appeared in a random event of evolution -- and means instead that early animal evolution began as a direct result of oxygen, according to a release.
"Oxygen was like a slow fuse to the explosion of animal life," the paper's co-author David Catling of the University of Washington, said in the release. "Around 635 million years ago, enough oxygen probably existed to support tiny sponges. Then, after 580 million years ago, strange creatures as thin as crêpes lived on a lightly oxygenated seafloor. Fifty million years later, [our] vertebrate ancestors were gliding through oxygen-rich seawater."
The study used new chemical tracers placed in rocks on three continents-in China, Australia, the U.S. And Canada. Sample sites in North America included the Uinta Mountains east of Salt Lake City, the Grand Canyon, and Canada's Northwest Territories' MacKenzie Mountains. They measured selenium isotopes in the rocks, learning about oxygen levels from 770 million years ago and going to 520 million years ago, a statement confirmed.
All in all, going from a level of 1 percent to over 10 percent of current oxygen levels took about 100 million years, the researchers said in their paper.
"We were surprised to see how long it took Earth to produce oxygen," lead author Philip Pogge von Strandmann of University College London said in the release. "Our findings dispel theories that it was a quick process caused by a change in animal behavior."
"Ultimately, a grasp of geologic controls on oxygen levels can help us understand whether animal-like life might exist, or not, on Earth-like planets elsewhere," Catling said in the release.
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