Published in the journal Science Advances, the research emphasizes the importance of exploring subsurface life forms to better understand the potential for extraterrestrial life.

The discovery of vast reservoirs of microbes located kilometers beneath the Earth's surface in the mid-1990s significantly altered our understanding of life on Earth.

Researchers at the Marine Biological Laboratory in Woods Hole have developed a global atlas of microbial diversity, analyzing over 1,000 genetic samples from 50 ecosystems worldwide.

After eight years of extensive study, the research identified an astonishing 31,000 unique types of archaea and over 377,000 unique types of bacteria, referred to as amplicon sequence variants (ASVs).

The findings reveal that subsurface microorganisms are surprisingly diverse, challenging the long-held belief that deeper environments support less life due to lower energy availability.

Lead author Emil Ruff noted that in some subsurface environments, microbial diversity can rival or even exceed that found on the surface, particularly in marine ecosystems.

The study highlights a clear ecological divide between marine and terrestrial microbes, which are influenced by different selective pressures in their respective environments.

Subterranean organisms derive energy through various methods, including organic matter scavenging, radioactive decay of rocks, and chemosynthesis, as they lack sunlight.

Interestingly, deep-Earth microorganisms operate on much slower timescales, with some cells dividing only once every 1,000 years, suggesting unique biological aging processes.

It is estimated that 50-80 percent of Earth's microbial cells are found in the subsurface, underscoring the hidden diversity of these life forms.

The study's findings imply that similar microbial life could exist in extreme environments elsewhere in the Solar System, such as beneath the surfaces of Mars, Europa, or Enceladus.