We may finally know what life on Earth breathed before there was oxygen

Billions of years ago, long before oxygen was readily available, the notorious poison arsenic could have been the compound that breathed new life into our planet.



a close up of a beach: La Brava microbial mats.


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La Brava microbial mats.

In Chile’s Atacama Desert, in a place called Laguna La Brava, scientists have been studying a purple ribbon of photosynthetic microbes living in a hypersaline lake that’s permanently free of oxygen.

“I have been working with microbial mats for about 35 years or so,” says geoscientist Pieter Visscher from the University of Connecticut.

“This is the only system on Earth where I could find a microbial mat that worked absolutely in the absence of oxygen.”

Microbial mats, which fossilize into stromatolites, have been abundant on Earth for at least 3.5 billion years, and yet for the first billion years of their existence, there was no oxygen for photosynthesis.

How these life forms survived in such

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