There’s Something Living In the Rocky Crust Beneath the Ocean Floor

Deep-ocean microbes could help us look for life on other planets.

In just about every nook, cranny, and crevice of our planet, some sort of life manages to thrive—whether it's under an Antarctic ice sheet, in super-salty Arctic water, or in Chile's Atacama desert, one of the driest and harshest environments in the world.

A US scientist has found something living in another surprising place: in the rocky sediment deep under the Atlantic Ocean, 50 to 250 meters beneath the seafloor, which is itself under 4.5 km—that's more than 2.7 miles—of ocean water. With no sunlight and few nutrients, not to mention extreme pressure, you won't find fish or many other creatures that deep.

These tiny microbes can eke out a living in deep ocean sediment and rock. Learning about them could help us find life in bizarre environments on other planets, too.

In the new paper, Julie Huber, associate scientist at the Marine Biological Laboratory in Woods Hole, Mass., describes the microbial community she and her team found way out at the bottom of the Atlantic. "It's the middle of the ocean," she told Motherboard. "Water, as far as the eye can see."

At North Pond in the mid-Atlantic, the ocean crust is young, and its circulating fluids are cold. Photo: Marine Biological Laboratory

Deep down underneath all that water is a sediment pocket called North Pond, on the western edge of the Mid-Atlantic Ridge. That's where new ocean crust is being formed as plates push apart. That crust isn't static, she continued. "Fluids are still moving through it," as seawater rushes through its crevices.

Samples were collected with the Integrated Ocean Drilling Program, an international project that drills deep into the seafloor for science—not the same as offshore oil drilling, although technologies have been swapped between the two.

For all the strangeness of the environment they live in, these microbes aren't necessarily "extremophiles," Huber said. "They appear to be closely related to [others found] in seawater. But we're finding genetic signatures suggesting they are slightly different," in ways that aren't yet understood. She and others are trying to piece that together now, studying their DNA.

Huber wasn't surprised to learn that something could live in a "cold crustal aquifer," as she calls this deep-ocean environment. (Most of her other work focuses on high-temperature hydrothermal vents and underwater volcanoes.) "It's pretty rare not to find microbes," she said. "They seem to find a way."

Given that life takes hold basically everywhere on our planet, could we find it on another one? Scientists are excited by the idea that they could one day find something living on Enceladus, an icy moon of Saturn. "Based on modelling, it looks like pretty much the only energy available there is methane and carbon dioxide," maybe a bit of hydrogen, said Huber, who's received NASA funding for some of her research. "Only a handful of microbes can use those on our planet, and they're pretty specialized."

By studying life in lower-energy environments—like the rock and sediment at the bottom of the ocean—we'll learn more about what tricks microbes use to eke out a living. Hopefully, it's preparation for one day getting to Enceladus.