Exploring Earth's 'Deep Biosphere' May Be Key to Understanding Extraterrestrial Life

Wednesday, 12 December 2018 - 12:29PM
Earth
Astrobiology
Wednesday, 12 December 2018 - 12:29PM
Exploring Earth's 'Deep Biosphere' May Be Key to Understanding Extraterrestrial Life
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U.S. Department of Agriculture – CC BY 2.0
Everyone is holding out hope that we'll eventually find intelligent life (even if it's a tiny, super-intelligent entity, like Silvano Colombano imagines), but a better bet is that we'll find alien bacteria long before we find a Kardashev III civilization. Sci-fi writers love to imagine exotic new forms of life, but in truth, those extraterrestrial microorganisms might bear a strong resemblance to life in Earth's 'deep biosphere,' where vast numbers of never-before-studied organisms have lived and evolved for billions of years.

The 'deep biosphere' consists of the subterranean sediment and rock that exists below the depth of the seafloor but above the Earth's core. As you can imagine, this constitutes a lot of space—about 500 million cubic miles. In fact, this vast, underground terra incognita dwarfs the oceans in sheer scale, and is estimated to hold between 17 and 25 billion tons of carbon-based biomass, roughly 300 to 400 times the biomass of all humans on Earth. So, what's down there?

Scientists don't know yet.

What they do know is that there is a lot of undiscovered life lurking in the deep parts of the Earth, and that it's managed to survive in incredibly hostile conditions. According to Fumio Inagaki, a geomicrobiologist at the Japan Agency for Marine-Earth Science: "Even in dark and energetically challenging conditions, intraterrestrial ecosystems have uniquely evolved and persisted over millions of years. Expanding our knowledge of deep life will inspire new insights into planetary habitability, leading us to understand why life emerged on our planet and whether life persists in the Martian subsurface and other celestial bodies."

So far, cyanobacteria have provided one of the most promising templates for what alien bacteria could look like, especially since the discovery that some types can photosynthesize without sunlight. There's been growing speculation that there might be life beneath the surface of Mars, but the recent InSight lander and the upcoming Mars 2020 mission won't be equipped to search for it.

Cover image: U.S. Department of Agriculture – CC BY 2.0
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