Geologists have gone down to the floor of the North Atlantic Ocean and drilled 1,268 meters below the seafloor, making this the deepest penetration into Earth’s mantle. It is through research vessel JOIDES Resolution that such an unprecedented feat has been accomplished, offering a unique glimpse into the outer layers of the planet, which may even explain the very origins of life.
It has numerous dissimilar layers: a solid outer crust, an upper and a lower mantle, and a core. The upper mantle lies directly under the crust and is largely composed of a magnesium-rich rock called peridotite. This layer plays a very important role in forcing major planetary events like earthquakes, water cycling, and the formation of volcanoes and mountains.
“Up until now, we’ve only seen crumbs of the mantle,” says Johan Lissenberg of Cardiff University. But some bits, such as the submarine mountain Atlantis Massif under the middle of the Atlantic Ocean, have bits of the mantle poking up through the sea floor—a volcanically active area, with hydrothermal vents spewing chemical compounds, including methane, that support microbial life.
Eisenberg and his colleagues had aimed to drill 200 meters into the mantle and ended up reaching 1,268 meters. “We recovered rong sections of continuous rocks and decided to stick with it and go as deep as we could,” said Andrew McCaig from the University of Leeds.
Analyses of the rock core revealed lower levels of a mineral called pyroxene, indicating extensive melting events at some time in the past within this mantle section. Eisenberg hopes to reconstruct this melting process to understand better how mantle melts and how molten rock migrates upward to vent onto the surface, thus fueling oceanic volcanoes.
Some scientists theorize life on Earth originated near hydrothermal vents in the depths of the ocean. Microbiologists are studying the chemicals along the rock core to see what conditions could have produced life and how far below the ocean floor those conditions existed. “It’s a very important drill hole because it’s going to be a reference section for scientists from many branches of science,” McCaig noted.
The expedition was led by Dutch geologist Johan Lissenberg, who had been part of the International Ocean Drilling Project Expedition involving 21 countries. A process where olivine becomes serpentine rocks, releasing hydrogen and methane called serpentinization, according to their findings in the journal Science, can create conditions suitable for microbial life.
Rémi Coltat, a French geologist on the expedition, called it “a window into the development of life on Earth.” Indeed, the JOIDES Resolution is only 143 meters long, and the research vessel is working day and night with scientists working 12-hour shifts to make the most out of the drilling effort.
The previous record for drilling into mantle rocks was a 200-meter borehole achieved three decades ago. “It was incredible when we saw that we could drill so well,” he recounted.
According to geologist Juan Manuel García Ruiz, the new study is important to understand the methane origin in such environments, either from bacteria or serpentinization reactions. German researcher Manuel Dominik Menzel commented that the upper mantle is a key to understanding magmatism and forming a continental crust.
This historic Atlantis Massif drill core advanced not only knowledge of Earth’s mantle but also is an emerging avenue toward investigating life’s origins and hence a milestone in geologic research.