Remnants of Life Found Half a Mile Below the Seafloor

Similar deep habitats might be found on other worlds.

The Lost City hydrothermal field in the mid-Atlantic.

Evidence for life keeps turning up in deeper and deeper places on our planet. Frieder Klein of the Woods Hole Oceanographic Institution and his colleagues report finding remnants of life in rocks that are 100 million years old, lying 700 meters (2,300 feet) below the ocean floor. The treasure trove of organic molecules recovered from the rocks includes proteins, amino acids, and lipids such as fatty acids. The molecules were fossilized in fractured rocks and became trapped within precipitating minerals.

The findings indicate that even below Earth’s crust, within its water-soaked mantle, a habitat for life can exist. Detailed analysis revealed that the organic markers of life were most similar to those seen in the Lost City field, a hydrothermal vent area in the Mid-Atlantic ridge, which was discovered in 2000.

The vents of the Lost City hydrothermal field are located on the Atlantis Massif, a seafloor mountain where reactions between seawater and Earth’s upper mantle produce lots of methane and hydrogen, compounds that microbes are eager to consume. The mantle rocks analyzed by Klein and his team are similar to Lost City, but different from the more common “black smoker” hydrothermal vents that typically release a lot of carbon dioxide, hydrogen sulfide and metals.

The new study shows not only that microbes have been very active at locations beneath the ocean floor, but also that life can be intrinsically connected to geological processes. The hydrothermal fluids at Lost City discharge into the ocean water due to seafloor spreading. Magma rises up, creates new oceanic crust, and pushes the oceanic plate apart, and the mixing of hydrothermal fluids and seawater in this zone leads to thriving microbial life.  The implication of the study is that the same thing occurred in mantle rocks from below the ocean crust, where hydrothermal water came in contact with seawater about 100 million years ago. That means the geological activity of our planet provides suitable conditions for life to thrive deep within.

We might therefore expect this to happen on other planets and moons, especially in places like Jupiter’s moon Europa, which has a deep subsurface ocean that is tidally kneaded and thought to be in direct contact with its rocky mantle.

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