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Apr 29, 2023

After 60 Years of Trying, Geologists Finally Pried Rocks From Earth's Upper Mantle

For 60 years, scientists have tried to get rock samples of the Earth’s mantle.

For 60 years, scientists have tried to get rock samples of the Earth's mantle. But the geologic layer below the planet's crust is incredibly difficult to reach.

Scientists believe they’ve successfully exhumed a 1,000-kilometer core sample that reaches into the very edge of the mantle.

Examining this rock could help scientists understand magma flows, earthquakes, and other geologic mysteries.

To understand the geologic processes roiling beneath the Earth's crust, it helps to have samples of what exactly is going on down there.

For more than 60 years, scientists have been trying to retrieve a rock from the upper mantle, but have failed to extract a large core sample. That, however, changed earlier this month when researchers onboard the JOIDES Resolution—the flagship vessel of the International Ocean Discovery Program (IODP) that's been scientifically scouring the ocean floor for decades—announced that they’d successfully retrieved a 1,000-kilometer-long core of rock from the Earth's upper mantle, consisting mainly of the rock peridotite.

"These are the types of rock we’ve been hoping to recover for a long time," project co-lead Susan Lang, a biogeochemist at the Woods Hole Oceanographic Institution, told Science.

Before this record-breaking sample, the largest hole drilled into serpentine peridotite was only 200 meters, which was retrieved back in 1993. Getting at mantle rock is an incredibly tricky process, seeing as the geologic layer is about 30 kilometers below the Earth's surface on average. But the Atlantis Massif—just east of the Mid-Atlantic Ridge—bucks that average and brings the mantle much closer to the Earth's surface through a process known as "ultra-slow seafloor spreading," which occurs where two tectonic plates move away from each other.

"This enables the JOIDES Resolution the unique opportunity to drill and bring up this mantle rock which has not been altered by weathering on the surface, allowing scientists to provide us with new insights into the composition and structure of the mantle, as well as processes that take place within it," the statement says.

The first attempt at gathering a core sample like this dates back to 1957 with Project Mohole—a reference to the Mohorovičić discontinuity, or Moho, which is a boundary between the Earth's crust and mantle. The project's goal was to reach the Moho via undersea drilling, as such samples would provide better evidence of geological activity due to reduced exposure to atmospheric and surface action. Sadly, Congress defunded the project in 1966 before Project Mohole could complete its mission.

Although some scientists question if this 1,000-kilometer core is a true example of mantle rock (influences of seawater seen in the rock, for example, have caused some to be suspicious), the sample is clearly a never-before-seen glimpse into Earth's geology. Scientists expect that this core sample could answer lingering questions about magma flows, earthquakes, mantle heat, and a variety of other topics.

"The magnitude of the history occurring has most certainly not been lost on our science party, many of whom are seasoned field researchers and believe this will be incredibly important data for many generations of scientists to come," the statement says.

Despite this incredible discovery, the National Science Foundation—which operates the JOIDES Resolution–says it’ll end its contract in 2024. It's also unlikely that Congress will approve a funding extension, despite arguments from participating researchers. But that doesn't mean the ship is ready for retirement—Japan and Europe are already planning a new drilling expedition set for 2025.

The geologic journey continues.

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