Scientists Extract Rocks From Earth’s Mantle

They drilled into a mountain at the bottom of the North Atlantic Ocean

A large ship sits at a dock
A picture taken in 2014 of the JOIDES Resolution, the ship used for the recent drilling expedition.  David Wong / South China Morning Post via Getty Images

Scientists have drilled a hole thousands of feet beneath the floor of the North Atlantic Ocean and extracted rocks from Earth’s mantle. It’s the deepest hole ever dug to collect mantle rock, according to a blog post from the expedition.

Below Earth’s crust lies the mantle—a layer of mostly solid rock around 1,800 miles thick that makes up 84 percent of the planet’s total volume. It’s mostly composed of silicates, compounds of silicon and oxygen. The mantle contributes to the evolution of the crust and plays a role in plate tectonics.

Scientists struggle to study the mantle. It lies around 20 to 25 miles below the Earth’s surface on land, making it impossible to drill to, according to the scientific prospectus for the current expedition. But deep at sea, the crust is only three to four miles deep.

The researchers aboard the JOIDES Resolution, the ship conducting the exploration, hope the extracted cores can help them better understand the composition and structure of the mantle, as well as processes that occur inside the mantle, according to the post.

It can also help scientists learn about the role magma plays in volcanism, Johan Lissenberg, a geologist at Cardiff University in Wales on the ship, tells Science’s Paul Voosen. “This could be a whole step forward for understanding magmatism—and the global composition of the bulk Earth,” Lissenberg tells the publication.

The researchers also hope the rocks can provide insight into how chemical reactions between mantle rocks and water may have created the first life on Earth, writes the Washington Post’s Carolyn Y. Johnson.

“These are the types of rock we’ve been hoping to recover for a long time,” Susan Lang, a biogeochemist at the Woods Hole Oceanographic Institution and a co-leader of the expedition, tells Science.

For the new mission, scientists drilled into the Atlantis Massif, a mountain at the bottom of the seafloor. The researchers were able to extract samples from over 4,100 feet below the seafloor after a month of drilling. The cores are largely made of peridotite, an igneous rock made of the minerals pyroxene and olivine, that is the most common type of rock in the upper mantle, per the Washington Post.

The deeper they drilled, the less the rocks had been altered by sea water. Rocks influenced by seawater could be considered to be from the deep crust instead of the mantle, Donna Blackman, a geophysicist at the University of California, Santa Cruz, tells Science.

“The deeper we get in there, the closer we’re getting to what we those rocks look like, closer to what the mantle looks like,” Jessica Warren, a geochemist at the University of Delaware who has been following the mission from land, tells the Washington Post.

Scientists theorize that the hydrogen created by reactions between olivine and seawater could have helped form organic molecules. “These are the building blocks of life,” Lang told the Wall Street Journal’s Dominique Mosbergen in February.

Preliminary investigations suggest that carbonate in the samples could show where more fluid flowed in the rock, and these sections could have been more favorable to life. The cores could also help with the study of earthquakes and how much heat the mantle produces, James Day, a geochemist at the Scripps Institution of Oceanography, tells Science.

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