An international team of scientists has uncovered a vast and unexpected diversity of microbes thriving deep beneath the Earth’s surface. The groundbreaking study, spanning eight years, found life forms living deeper than ever recorded.
Microbial ecologist Emil Ruff from the Woods Hole Oceanographic Institution in the US and bioinformatician Isabella Hrabe de Angelis from the Max Planck Institute for Chemistry in Germany led the study. They revealed microbes as deep as 491 meters (1,610 feet) below the ocean floor and up to 4,375 meters (2.7 miles) underground on land.
MAPPING THE DEPTHS OF LIFE
Researchers collected samples from over 50 locations worldwide. They studied soils, sediments, water columns, deep-sea hydrothermal vents, caves, boreholes, aquifers, and even fracking fluid. This extensive survey provided a rare glimpse into the unseen biosphere beneath Earth’s crust.
Surface samples came from traditional environments like soil and water. Subsurface samples, nevertheless, required deep drilling into boreholes and mines, revealing life that had adapted to extreme conditions.
LIFE DEFIES EXPECTATIONS BELOW GROUND
Conventional wisdom suggests that life should diminish with depth due to decreasing energy availability. But, the study defied this assumption.
“The deeper we explored, the more we found,” said Ruff. “In some environments, microbial diversity rivaled, if not exceeded, that of the surface.”
Marine environments, in particular, harbored an astonishing variety of bacteria and archaea. The latter became more genetically diverse the deeper the team ventured.
HOW MICROBES SURVIVE IN THE DEEP BIOSPHERE
Sunlight never reaches these underground worlds, forcing microbes to rely on alternative energy sources. They extract energy from hydrogen, methane, sulfur, serpentinization, decaying organic material, and even radioactivity.
This adaptation results in an incredibly slow-moving ecosystem. Scientists estimate that some of these deep-dwelling microbes divide only once every thousand years.
“Their metabolism is fine-tuned for efficiency,” Ruff explained. “These microbes have evolved to survive with minimal energy, making them uniquely suited for life in extreme conditions.”
A CONTINUUM OF LIFE FROM SURFACE TO DEPTHS
Analysis of 478 archaea, 964 bacteria, and 147 metagenomes showed that surface and subsurface life exist on a continuum. These forms of life are not separate ecosystems.
Yet, stark differences emerged between marine and terrestrial life forms. Each environment imposes unique pressures that shape microbial evolution.
“Land and sea select for different organisms,” said Ruff. “These microbes struggle to survive outside their respective domains.”
DATA GAPS AND FUTURE RESEARCH
While the study provided an unprecedented look into deep microbial life, some environments remain underexplored. Marine surface samples yielded an abundance of data, whereas information from caves and deep soils remains scarce.
Filling these gaps will be essential for understanding life’s full diversity beneath Earth’s surface.
IMPLICATIONS FOR LIFE BEYOND EARTH
The study’s findings extend beyond Earth’s boundaries. If microbes can survive miles underground here, they might also exist on other planets.
“Understanding deep Earth life gives us a model for detecting life on Mars,” Ruff suggested. “Liquid water could support subsurface microbial ecosystems just meters below the surface of other planets.”
If extraterrestrial life exists, we might need to dig deep to find it.