In a geological triumph, scientists are drilling a window into the Earth’s mantle

The new campaign, by an ocean drilling ship called JOIDES DECISIONIt wasn’t technically drilled into the mantle, and the hole wasn’t the deepest ever drilled beneath the ocean floor. Instead, the researchers dug into a special “tectonic window” in the North Atlantic where the drill doesn’t have to tunnel so much as hit dirt. Here, mantle rock has been pushed closer to the surface as the ocean floor is slowly disintegrating at the nearby Mid-Atlantic Ridges.

On May 1, they began digging the hole, known as the U1601C. Andrew McKeag, the mission’s chief scientist, expected to make a shallow “hole” because the record for drilling in mantle rock, set in the 1990s, was just a tenth of a mile. The researchers hoped to recover enough samples to help explain how chemical reactions between mantle rocks and water could give rise to life on our planet. But ocean drilling can be an uncertain venture—drills get stuck, or the long rock samples recovered may be only partial samples.

This time, though, the drill yielded tube after tube of dark rock, many of which were surprisingly complete.

It just kept going deeper and deeper and deeper. Then everyone at the science party said, “Hey, this is what we wanted all along. Since 1960, we’ve wanted to get a deep hole in the mantle rock. When the team stopped drilling on June 2, the team took rock samples from 4,157 feet below the sea floor.

“We’ve fulfilled an ambition that has fueled the scientific community for many decades,” said McKeag.

Scientists on Earth have been eagerly watching the mission, anticipating the jackpot from data that will open a new window into Earth’s depths and fuel years of research.

said Andrew Fisher, a hydrogeologist at the University of California, Santa Cruz, who advises a graduate student who was on the ship and has been spotted. remote progression.

In 1909, Croatian seismologist Andrija Muhorovicic discovered a boundary within the Earth.

The Mohorovii monitored how seismic waves generated by an earthquake travel through the Earth, similar to using X-rays to probe the inside of a human body. Near the surface, the seismic waves were traveling at a single speed, but after a certain area around the world, they were moving faster, indicating that the waves were traveling through two distinct layers of rock.

This discontinuity, called moho, is now recognized as The line separating the Earth’s crust from its mantle. Its depth varies, but the mantle generally starts about five miles below the ocean floor and about 20 miles below the continents.

said Jessica Warren, a professor of geosciences at the University of Delaware who was also monitoring the Progress Telemetry Project. “If we want to understand the Earth as a whole, there is a huge, huge amount of rock underneath.”

The Earth’s inner core appears to be slowing its rotation

Mantle is not completely unknown. Occasionally, volcanic eruptions spew out bits of it—chunks of greenish peridot, the type of rock that dominates the upper mantle, embedded in basaltic rocks. But these samples, called mantle xenolithsHowever, it has its limitations, as it is often chewed and hollowed out from its journey to the surface. There are also ophiolites, which are sheets of oceanic crust tinged with some of the upper mantle that have been lifted and glued to the Earth. But the journey has changed, too.

What scientists have long yearned for is a fossilized sample of mantle rock. Mohole projecta famous ocean expedition, set out to drill through the thin crust on the ocean floor to reach the mantle in 1961 but failed.

Parts of the ocean floor where the mantle is closest to the surface seemed like an opportunity to take a sample without the technical difficulties of drilling through miles of crust. This is where the scientists aboard JOIDES Resolution set their sights on one of the ship’s final missions ahead of it scheduled retirement In fiscal year 2024.

The team left Ponta Delgada in Portugal’s Azores in April and headed to the Atlantis Massif, an underwater mountain the size of Mount Rainier. Its primary mission was not to drill the deepest hole yet in mantle rocks, but to sample those rocks for clues about how, in the absence of life on Earth, small organic molecules form when rocks interact with water.

“This could be a way you can take it from just basically getting water and rocks,” said Susan Lang, the expedition’s chief scientist and a scientist at Woods Hole Oceanographic Institution. produces hydrogen, [and] That hydrogen is a really great fuel for things like making smaller organic molecules, and it can then combine with other organic molecules and lead to early life.”

Deepening and recovery

The rock core excavated from crater U1601C is dominated by peridotite, the most common type of rock found in the upper mantle. her samples It has been altered by its exposure to sea water, scientists We have already begun to discuss how to interpret the results.

Most of the mantle is buried under the crust, not exposed to the ocean as it is at this site. This raises a fundamental question: How well do recent samples mimic the rest of the mantle? Do the rocks Does it really represent the mantle, or is it crust-less?

For that matter, is the mantle-crust boundary sharp, or is it a more gradual transition? The samples are not pure peridotite, and this can be a key clue.

“It’s kind of fragmentation, but maybe that’s the bottom crust,” Fisher said, listing different types of rock reported in the Science Daily Annals. “This is really unusual — more than a kilometer of very altered lower crust and/or upper mantle rock. I would say it’s a mixture.”

Scientists have been so busy processing the sheer volume of rock they’ve recovered that they haven’t had a chance to study the samples in detail, or even consider the scale of the achievement. Drill bits need to be replaced every 50 hours. The team on board works in 12-hour shifts, without losing a minute of time.

One morning, Lang becomes distracted and excuses herself from an interview when she sees sea water splashing through the window.

“I’ve seen this stage of seawater, which was always a very exciting point where they separate this thing from a bunch of seawater sprays all over the place,” Lang said. “Normally, this is my warning that a nucleus is coming on deck within the next five minutes.”

What excites them all is the hope that deeper samples will yield “fresher” rocks, less altered by other processes and closer to what the mantle is forming.

“The deeper we go there, the closer we get to what those rocks look like, closer to what the mantle looks like,” Warren said.