Isegoria

In May of 2023, scientists drilled the deepest core yet and recovered serpentinized peridotite that forms when saltwater interacts with mantle rock:

Separating the planet’s rocky crust and the molten outer core, the mantle makes up 70 percent of the Earth’s mass and 84 percent of its volume. But despite its outsized influence on the planet’s geologic processes, scientists have never directly sampled rocks from this immensely important geologic layer.

And that’s understandable, especially when you consider that the crust is roughly 9 to 12 miles thick on average. Luckily, that average contains outliers—areas of the world where the crust is actually incredibly thin and faulting exposes the mantle through cracks. One such area is the Mid-Atlantic Ridge, specifically near an underwater mountain called the Atlantis Massif.

On the south side of this massif is an area known as the Lost City — a hydrothermal field whose vent fluids are highly alkaline and rich in hydrogen, methane, and other carbon compounds. This makes the area a particularly compelling candidate for explaining how early life evolved on Earth. Additionally, it contains mantle rock that interacts with seawater in a process known as “serpentinization,” which alters the rock’s structure and gives it a green, marble-like appearance.

It was here, 800 meters south of this field, in May of 2023 that members of the International Ocean Discovery Program (IODP) — aboard the JOIDES Resolution, a 470-foot-long research vessel rented by the U.S. National Science Foundation — extracted a 1,268-meter core containing abyssal peridotites, which are the primary rocks that make up the Earth’s upper mantle.

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“We had only planned to drill for 200 meters, because that was the deepest people had ever managed to drill in mantle rock,” Johan Lissenberg, a petrologist at Cardiff University and co-author of the study, told Nature. He said that the drilling was so easy that they progressed three times faster than usual. The team eventually drilled a staggering 1,268 meters, and only stopped due to the mission’s limited operations window.

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