Welcome to Quantum Magazine's podcast.

Each episode, we bring you stories about developments in science and mathematics.

I'm Susan Vallett.

Scientists have come to realize that in the soil and rocks beneath our feet, there lies a vast biosphere

with a global volume nearly twice that of all the world's oceans.

We don't know much about these underground organisms, but they represent most of the planet's

microbial mass, and their diversity may exceed that of surface-dwelling life forms.

But they come with a puzzle.

That's next.

Quantum Magazine is an editorially independent online publication supported by the Simons Foundation

to enhance public understanding of science.

The existence of Earth's microbes comes with a great puzzle.

Researchers have often assumed that many subterranean realms are oxygen-deficient dead zones

inhabited only by primitive microbes that keep their

metabolisms at a crawl and scrape by on traces of nutrients. It was thought as those resources

get depleted, the underground environment must become lifeless with greater depth.

In new research published this summer in Nature Communications, researchers

presented evidence that challenges those assumptions. In groundwater reservoirs 200 meters below

the fossil fuel fields of Alberta, Canada, they discovered abundant microbes that produce

unexpectedly large amounts of oxygen, even in the absence of light.

Researchers call it dark oxygen.

Karen Lloyd is a subsurface microbiologist at the University of Tennessee, who wasn't part of the study.

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