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Scientists have discovered an amazing microbial diversity deep below Earth’s surface that could have implications for the search for life on Mars.

The study, published in Science Advances, examined microbes from up to 3 miles underground and 1,600 feet below the sea floor.

These organisms thrive in extreme, low-energy environments—conditions that could mirror those on Mars or other planets with subsurface ecosystems.

The research, led by Emil Ruff, is the first large-scale comparison of marine and terrestrial subsurface microbiomes, offering insight into possible adaptations of extraterrestrial life.

“Three kilometers below the surface of Earth and Mars look very similar, so we understand the subsurface life of the Earth[…]will provide clues as to what to look for in other celestial bodies.”

Why it matters

The findings have important implications for the search for extraterrestrial life.

If Mars or other rocky planets ever had liquid water beneath the surface, the ecosystems there could resemble Earth’s deep biosphere.

The study also highlights that life can persist with minimal energy, with microbial cells sinking much more slowly than at the surface.

Understanding these adaptations could improve future astrobiological missions in the search for signs of life.

“It’s fascinating that in these low-energy environments, life seems to be slowed to an absolute minimum,” Ruff said in a statement. “Some subsurface cells only divide once every 1,000 years. So these microbes have completely different life time scales.”

What to know

Microbes in the Earth’s subsurface have evolved to survive on almost no energy. Their metabolism is tuned to be incredibly efficient.

Research has revealed that microbial diversity underground can rival or even exceed surface ecosystems such as coral reefs.

Scientists estimate that 50 to 80 percent of Earth’s microbial cells may live in these underground ecosystems.

“We can now also appreciate that perhaps half of the microbial diversity on Earth is in the subsurface,” Ruff said.

These environments are inhospitable places to live, with little energy or heat to sustain biological processes.

“It makes sense to be evolutionarily adapted to absolutely minimize your energy and energy requirements and optimize every single part of your metabolism to be as energy efficient as possible,” Ruff said.

“And we can also learn from it: How to be extremely efficient when working with next to nothing.”

Mars itself was once covered in water, and the rocky ecosystems assessed in this study likely reflect those miles below the red planet’s surface.

Ruff added: “The energy would be very low; the generation time for organisms would be very long. Understanding deep life on Earth could be a model for finding out if there was life on Mars and if it survived.”

Subsurface marine environments have been found to be particularly teeming with microbial life. Archaea—microorganisms similar to, but evolutionarily distinct from, bacteria—thrive in these realms.

Archaea are ancient life forms known to survive in some of the most extreme environments on the planet, such as the boiling thermal pools of Yellowstone National Park.

“However, the surprising thing is that subsurface life is very similar to surface life. We have not found any true aliens — major lineages that have no representatives in any of the surface environments,” Ruff said.

“Subsurface microbes are similar to those on the surface, so there has to be either a trade-off, or the evolution of microbes in the subsurface is too—much like everything else—in the slow lane.”

Link

S. Emil Ruff et al. (2024) Global comparison of surface and subsurface microbiomes reveals large-scale biodiversity gradients and the marine-terrestrial divide. Science Advances, DOI: 10.1126/sciadv.adq0645

Fix 12/19/24 4:33AM ET: The image of the people in the mine was given the correct caption and authority.

Update 12/19/24 4:40 AM ET: The article has been updated with comments from Emil Ruff.