Rocks on the floor of the Atlantic Ocean hold many secrets that could help scientists understand our planet and the origins of life on it. That’s why a group of researchers has undertaken a difficult task: They dug a hole more than three-quarters of a mile deep and extracted a record core of rock from the Earth’s mantle.
Scientists regularly take core samples – cylindrical samples of material from deep within the Earth’s surface – to study the composition of different layers. This data can act as a window into the planet’s past, providing information about climate and environmental changes or the formation of the Earth itself. Drilling in the deep sea presents special challenges, so researchers have often been forced to dredge rocks from the sea floor. Analyzing the composition of these rocks can provide valuable information, but these rocks can be altered by the pressure of the sea and by exposure to salt water.
The expedition took place between April and June 2023 in an area of the North Atlantic known as the Atlantis Massif, an underwater mountain that rises 4,267 meters above the sea floor. The site was chosen because tectonic activity in the area pushes rock that is normally deep in the Earth’s mantle much closer to the sea floor, making it easier to recover. Even so, some deep drilling was required to obtain a 1,268-meter-long, nearly continuous core of peridotite, a type of igneous rock.
This extreme depth is far greater than any previous attempt to drill into oceanic mantle rocks. According to the study, which also included C. Johan Lissenberg of Cardiff University, scientists managed to recover 71% of the drilled material, with long sections of partially serpentinized harzburgite (that is, rock partially altered by water) almost completely recovered.
As mentioned in the article published in the journal, ScienceThe researchers analyzed the composition of minerals in the rock and found evidence for a theory about how rocks formed deep in the Earth’s mantle reach the surface. According to this theory, pressure melts rock, which is then pushed upward and mixes with magma in the Earth’s crust before erupting on the seafloor.
The researchers also discovered intrusions of a crystalline rock called gabbro, which is formed by the slow cooling of magma. They believe gabbro plays an important role in regulating the minerals and gases found in deep-sea vents, which some scientists believe provide an ideal environment for primitive life to emerge. Learning more about these vents could lead to new theories about how life began on Earth and how it could theoretically arise on other planets.
In the study, the researchers acknowledged that the rocks they drilled still need to be analyzed in much greater detail. “The comprehensive rock record obtained during Expedition 399 offers a wealth of opportunities to fundamentally improve our understanding of the Earth’s upper oceanic mantle,” they said.
In an accompanying article, Eric Hellebrand, a professor at Utrecht University, said the “depth far exceeds those found in previous drilling and offers the opportunity to identify structural and mineralogical features of the Earth’s mantle and its interaction with the hydrosphere and biosphere.”
He also expressed the hope that the drilling expedition could set new standards for research into the formation of the Earth.
“Decades of seafloor dredging sampling have painted a rough mineralogical picture of the Earth’s mantle,” he wrote. “But each new drilling mission reveals surprising insights into the mantle and the formation of the oceanic crust. More sophisticated drilling projects will provide important insights into understanding the biogeochemical impacts of the oceanic mantle.”
