Scientists drill record 3937 feet into Earth’s mantle to unveil life origins

Researchers at the Woods Hole Oceanographic Institution in the US and Cardiff University in the UK have drilled a three-quarter-mile (1.268 km) long core from the Mid-Atlantic Ridge. This record-breaking mineralogical recovery from the mantle could help scientists unlock the secrets to the origin of life on Earth.

“Our hole is the deepest in mantle rocks; previously, the deepest hole in upper mantle rocks was 200 m (656 feet),” Johan Lissenberg, a professor at Cardiff University, told Interesting Engineering via email.

“It is not the deepest hole in the world: the Kola Superdeep Borehole is the deepest drill hole on Earth at >12 km. But that is on land, where drilling is a lot easier than from a ship.”

The nearly continuous mantle rock containing serpentinized abyssal mantle peridotite, a primary rock in the mantle, was recovered during Expedition 399 of the ocean drilling vessel JOIDES Resolution in the Spring of 2023.

The expedition was led by the International Ocean Discovery Program (IODP), a consortium of marine researchers from more than 20 countries.

Previous attempts at studying mantle cores relied on samples dredged from the seafloor. However, these samples lacked spatial context and continuity, much like individual pieces of a puzzle.

“Our long and largely continuous section enables us to look at the mantle in context and hence see the whole puzzle,” added Lissenberg.

The IODP has been compiling an inventory of mantle cores in Bremen, Germany, to understand their composition and structure.

How was the record-breaking core drilled?

Mantle cores are drilled by sending a drill string from the ship to the seafloor and drilling directly into the seabed. The technology has existed for a long time but has only yielded fragmented cores.

“On our expedition, we encountered extremely favourable drilling conditions, with deep penetration and very high recovery,” Lissenberg added in the email.

The researchers drilled 16-foot (five-meter) sections at a time using a rotary core barrel (RCB) drill , after which a core catcher was sent down the drill string to retrieve the core.

When the core is logged, the scientists onboard can study it, but at the end of the expedition, it is sent to the IODP core repository in Germany, where scientists study it further.

What did the researchers find?

The researchers found significant variability in the mantle’s mineralogy, with the abundance of orthopyroxene varying from a few centimeters to hundreds of meters, while its sister mineral, clinopyroxene, is almost absent.

The researchers attribute these differences to the flow of melt through the upper mantle, which rises beneath the tectonic plates and later feeds volcanoes . Yet, the levels of orthopyroxene in the sample are lower than anticipated, which is likely due to a greater degree of melt. The researchers are keen to determine when the melt occurred, whether in the recent millions of years or much earlier in Earth’s history.

The researchers also noticed hydrothermal fluid-rock interaction throughout the core with oxidative weathering down to 650 feet (200 m). The observation shows that seawater and rock interaction was very active at these depths.

“This is important because the reaction between seawater and mantle rocks releases hydrogen, forming compounds such as methane, which underpin microbial life. This is one of the hypotheses for the origin of life on Earth,” Lissenberg told IE .

The record-breakingly long drill core of the mantle will help researchers study such reactions in greater detail and link them to observations of microbial life in the rocks.

The research findings were first published in the journal Science .