Signs of life found in Earth's mantle

Scientists have collected an unprecedented sequence of rock samples from the shallow mantle of the Atlantic Ocean that bear signs of life, unique carbon cycling, and ocean crust movement.

During a 47-day expedition to collect rock cores from the Atlantis Massif, a 4,000 metre tall underwater mountain along the Mid-Atlantic Ridge, researchers collected rock samples using seabed rock drills from Germany and the UK - the first time the technology has been utilised in ocean drilling.

The aim of the expedition was to determine how mantle rocks are brought to the seafloor and react with seawater - such reactions may fuel life in the absence of sunlight, which may be how life developed early in Earth's history, or on other planets.

The team also hopes to learn more about what happens to carbon during the reactions between the rocks and the seawater - processes that could impact climate by sequestering carbon.

"The rocks collected on the expedition provide unique records of deep processes that formed the Atlantis Massif," said Co-Chief Scientist Gretchen Fruh-Green from ETH Zurich in Switzerland.

"We will also gain valuable insight into how these rocks react with circulating seawater at the seafloor during a process we call serpentinisation and its consequences for chemical cycles and life," Fruh-Green said.

"During drilling, we found evidence for hydrogen and methane in our samples, which microbes can 'eat' to grow and form new cells," said Co-Chief Scientist Beth Orcutt from Bigelow Laboratory for Ocean Sciences in US.

"Similar rocks and gases are found on other planets, so by studying how life exists in such harsh conditions deep below the seafloor, we inform the search for life elsewhere in the universe," Orcutt said.