Welcome to Quantum Magazine's podcast.

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

I'm Susan Vallett.

Earth and its sediments deep below where the light doesn't shine hold many mysteries,

but scientists think they've cracked one of them. And it could have

implications for life on other planets. That's next.

Explore other science mysteries in the Quanta book Alice and Bob Meet the Wall of Fire,

published by the MIT Press. Available now at Amazon.com,

Barnes & Noble.com, or your local bookstore. Also, make sure to tell your friends about the

Quantum Magazine Science Podcast and give us a positive review or follow where you listen. It helps

people find this podcast.

Scientists poke and prod at the fringes of habitability in pursuit of life's limits.

To that end, they've tunneled kilometers below Earth's surface, drilling outward from the bottoms of mine shafts and sinking boreholes deep into ocean sediments.

Tori Holer is a chemist and astrobiologist at NASA's Ames Research Center. He says to their surprise,

life was everywhere that they looked, and it was present in staggering quantities. By various estimates,

the inhabited subsurface realm has twice the volume of the oceans, and the number of cells it contains is estimated to be 10 to the 30th power.

That's a million, trillion, trillion. That makes it one of the biggest habitats on the planet, and one of the oldest

and most diverse, too. Researchers are still trying to understand how most of the life down there

survives. Sunlight for photosynthesis can't reach such depths, and the meager amount of organic

carbon food that does is often quickly

exhausted. Communities of organisms that dwell near hydrothermal vents on the sea floor, or

within continental regions warmed by volcanic activity, can rely on high-temperature processes

...