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Microbes Living in Deep Sea Rocks Spawn More Hope for Life on Mars

Starved of resources, these hardy bacteria still eke out a living, suggesting life forms could survive in the harsh habitats on other planets

A rock samples collected during a 2010 drilling expedition in the South Pacific that found microbes in the sea floor. (Caitlin Devor, The University of Tokyo, CC BY 4.0)
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Despite their microscopic size and simplistic cells, bacteria are some of the hardiest life forms around. In recent years, scientists have uncovered these stalwart microbes in environments as extreme as the searing hot springs in Yellowstone National Park and the acidic, metal-rich waters that drain out of mines.

Now, microbiologists plumbing the depths of the ocean can add another hostile habitat to the list of unexpected bacterial abodes: in tiny, ancient fractures of Earth’s crust beneath the South Pacific Ocean—some as old as 104 million years in age, reports Robin George Andrews for National Geographic.

Starved of warmth, nutrients and other crucial resources, these mysterious microbes have managed to eke out a living, and researchers still aren’t entirely sure how, they write in a study published last week in the journal Communications Biology. But solving that riddle could bolster the search for extraterrestrial life—past or present—on Mars, where similar rock-based ecosystems are thought to exist.

“I am now almost over-expecting that I can find life on Mars,” study author Yohey Suzuki, a researcher at the University of Tokyo, says in a statement.

Microbes have been found deep beneath Earth’s ocean floors before. Recent drilling experiments have revealed a surprising wealth of diversity in these rocky underwater environments, where bacteria are thought to leach nutrients from seawater.

At these depths, the most nourishing environments are those near mid-ocean ridges, networks of volcanoes that still actively belch up hot, young, metal-rich rock that quickly mixes with the cold, salty ocean water. Bacteria can take advantage of these chemical reactions to make their own energy.

Further out from these ridges, the scarcer these reactions—and the nutrients they generate—get. Scientists long assumed that the chances of finding microbial life would dwindle, or perhaps even disappear, in these regions as well. But a few years ago, a team led by Suzuki was surprised to find that ancient hunks of crust that had formed many millions of years ago still housed a population of microbial tenants, teeming in the tiny cracks that appeared in the rocks as they cooled.

Unlike other crust-living microbes, these bacteria can’t take advantage of the chemical reactions in seawater to survive. Instead, the researchers found, they seem to capitalize on the mineral-rich clay accumulating in the cracks they live in, reports Nick Carne for Cosmos.

In the statement, Suzuki describes the clay as “magic material” that can concentrate nutrients in small spaces, supporting life in even the unlikeliest of places. Though the researchers aren’t completely sure where the clay comes from, two likely sources exist: decomposing remains of marine life forms that live closer to the ocean surface, or the Earth’s crust itself, which is thought to break down over time.

The team also uncovered methane-munching microbes in the rocks, though the source of their food is less clear, according to National Geographic.

That these plucky little organisms exist at all is encouraging for researchers hunting for signs of life elsewhere in the solar system. Both volcanic rocks and methane abound on the Red Planet, providing potential fodder for enterprising Martian microbes. Encouragingly, the chemical composition of the rocks on the two planets are fairly similar, Arya Udry, a planetary scientist at the University of Nevada, Las Vegas who wasn’t involved in the study, tells National Geographic.

Mars may even have traces of a long-gone ocean beneath its surface, stockpiling nutrients in its cracked crust a bit like Earth’s seawater has done. Perhaps life once existed in those waters. Perhaps it never left. As Mark Lever, an ecologist at Aarhus University who wasn’t involved in the study, tells National Geographic, “If life existed on Mars in the past, it seems like it would also be very likely to exist today in these deep subsurface environments.”

About Katherine J. Wu
Katherine J. Wu

Katherine J. Wu is a Boston-based science journalist and Story Collider senior producer whose work has appeared in National Geographic, Undark magazine, Popular Science and more. She holds a Ph.D. in Microbiology and Immunobiology from Harvard University, and was Smithsonian magazine's 2018 AAAS Mass Media Fellow.

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