Deepest core drilled near Earth’s mantle reveals Earth’s geological secrets
- To understand the mantle – the largest layer of the Earth’s rocky body – scientists drill deep cores out of the Earth.
- In May 2023, scientists drilled the deepest core yet and found serpentinized peridotite, which is formed when salt water reacts with mantle rock.
- Although this is the deepest drilling into the Earth’s mantle that scientists have ever undertaken, the mission failed to uncover pristine mantle beyond the Mohorovičić discontinuity, or Moho boundary.
If you want to understand the geology of our home planet, studying the Earth’s mantle is a good place to start. The mantle, which separates the planet’s rocky crust from its molten outer core, makes up 70 percent of Earth’s mass and 84 percent of its volume. Yet despite its enormous influence on the planet’s geological processes, scientists have never directly taken rock samples from this immensely important geological layer.
And that’s understandable, especially when you consider that the crust is, on average, about 14 to 19 kilometers thick. Fortunately, there are outliers in that average – areas of the world where the crust is actually incredibly thin and faults expose 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 source fluids are highly alkaline and rich in hydrogen, methane and other carbon compounds. This makes the area a particularly compelling candidate for explaining the early evolution of life on Earth. In addition, it contains mantle rock that reacts with seawater in a process known as “serpentinization”, changing the structure of the rock and giving it a green, marble-like appearance.
Here, 800 meters south of this field, members of the International Ocean Discovery Program (IODP) discovered in May 2023 on board the JOIDES resolution, A 470-foot-long research vessel leased by the U.S. National Science Foundation has extracted a 4,100-foot-long core containing abyssal peridotites, the primary rocks that make up the Earth’s upper mantle. The study’s results were released last week. in the Journal Science.
Although this particular core is the deepest sample of the Earth’s mantle to date, the goal of this record-breaking expedition was not to penetrate so deep into the rock.
“We only planned to drill 200 meters deep because that was the deepest depth humans had ever drilled into mantle rock,” said Johan Lissenberg, a petrologist at Cardiff University and co-author of the study. NatureHe said the drilling was so easy that they progressed three times faster than usual. The team ultimately drilled an incredible 1,268 meters, only aborting the drilling due to the mission’s limited time window.
Andrew McCaig – co-author of the study and scientist at the University of Leeds – said in an article by The conversation that according to a preliminary analysis of the rock, the core contains a peridotite variant called harzburgite, which is formed by partial melting of mantle rock. It also contained gabbros, coarse-grained igneous rocks. Both rocks then reacted chemically with seawater, changing their composition.
While this core represents an incredible opportunity to learn more about the Earth’s mantle and gain a detailed look at the geological substrate upon which the Lost City rests, the mission did not quite meet the “grand challenge” of crossing the Mohorovičić Discontinuity. The Mohorovičić Discontinuity, also known as the Moho, is considered the true boundary between the Earth’s crust and the primordial mantle.
Future missions may further explore this location near the Atlantis massif, but unfortunately these missions will not include JOIDES Resolution– the NSF declined to fund further core drilling after 2024. While scientists are finally knocking on the door to Earth’s most widespread geological layer, the future of these types of drilling missions is now uncertain.
Darren lives in Portland, has a cat, and writes/edits about science fiction and how our world works. You can find his previous work at Gizmodo and Paste if you look hard enough.
