LSU Professors Join Historic Effort to Drill Earth's Mantle and Retrieve Rare Deep-Earth Samples

Beneath our feet lies a hidden world of searing rock, constantly churning and shifting, driving the slow yet relentless movement of Earth’s tectonic plates. The mantle, positioned between the crust and the core, powers volcanoes, can flow like honey or break in earthquakes, and even forms diamonds. Despite comprising 84% of the planet's volume, this vast layer remains largely a mystery. Now, a groundbreaking expedition—including two LSU professors—has successfully drilled into the mantle, recovering rocks never before observed. Their discoveries could transform our understanding of plate tectonic processes, natural hazards and uncover potential new energy resources.

Aboard the research vessel JOIDES Resolution, the International Ocean Discovery Program (IODP) Expedition 402 set out to drill into the Earth’s mantle—an endeavor attempted only a handful of times before. Since the late 1950s, scientists have attempted to drill through the Earth's crust to reach the mantle, but extreme heat and pressure have made it challenging. Only six prior expeditions have succeeded in recovering mantle samples. Instead, researchers, including LSU Assistant Professors Brandon Shuck and Eirini Poulaki, decided to seek out a “tectonic window”—a rare location where mantle rocks are naturally pushed closer to the surface.

This approach proved successful. “In IODP 402, we recovered important samples to study how continents break apart and how deep Earth interacts with the oceans and atmosphere,” said Shuck. “We recovered the second longest section of mantle rocks ever obtained through scientific ocean drilling—only surpassed by IODP Expedition 399.”

The expedition targeted the Tyrrhenian Sea, a geologically young region between Italy, Sicily, and Corsica, where complex tectonic forces have stretched and pulled apart the Earth’s crust within the past five million years. Unlike other regions where thick layers of sediment make mantle access nearly impossible, the Tyrrhenian Sea offers a rare and relatively unaltered glimpse into Earth’s interior.

This made it an ideal drilling site. Mantle rocks are rarely exposed at the surface, and when they are, their original properties are often altered by tectonic activity. “The Tyrrhenian Sea is one of the rare places where the mantle is somewhat exposed without being overprinted by later tectonic events. A not-so-thick layer of sediment—200 to 1,000 meters—covers it, which still makes simple dredging impossible. But once we drill through, the first hard rocks we reach are mantle samples, preserving a clearer record of past geological processes," explained Poulaki.

One of the team’s key findings, recently published in Nature Communications, challenges existing mantle melting theories and findings from previously collected mantle samples.

“Our results show a very heterogenous mantle, that is significantly more chemically and structurally complex than previously thought, which has critical implications for plate tectonic processes,” said Shuck.  

Typically, when tectonic plates pull apart, mantle rocks are drawn upward, where they begin to melt, transforming into a depleted type of mantle that ultimately forms magma and new oceanic crust. However, in the Tyrrhenian Sea, scientists found fertile mantle rocks that should have produced large amounts of magma—but they didn’t. This unexpected discovery raises new questions about how ocean basins form and how the mantle’s composition influences the process.

While previous expeditions have drilled into the mantle in mature ocean basins, such as the Atlantic, the latest study provides a unique glimpse into the mantle's composition during the early formation of an ocean. This distinction is critical because the mantle’s characteristics change over time as an ocean basin evolves.

“It's hard to know for certain, but the rock samples we recovered may be more representative of the mantle during the initial stages of an ocean basin forming,” says Shuck. “When an ocean first opens, the mantle hasn't undergone as much melting and is likely more heterogeneous. Most previous mantle drilling has been in areas where oceans have been spreading for hundreds of millions of years, making the mantle more homogeneous—one that has already been melting to a greater extent."

Another key scientific opportunity presented by the recovered samples is the study of serpentinization, a chemical reaction where mantle rocks interact with seawater to produce hydrogen and methane. These gases are essential for deep-sea microbial life and may have played a pivotal role in the origins of life on Earth. Beyond their biological importance, the byproducts of serpentinization also influence geological hazards. Water released from these altered rocks can trigger earthquakes and impact magma formation. Additionally, the hydrogen produced through this process has garnered interest as a potential clean energy source, offering valuable insights into natural hydrogen generation and its possible applications.

The expedition also revealed evidence that mantle rocks can naturally capture and store carbon dioxide. The recovered samples contained carbonate-filled veins, suggesting that natural CO₂ had crystallized in narrow cracks and got trapped within the rocks permanently. If scientists can replicate this process on a larger scale, it could provide a method for long-term carbon sequestration, offering an important tool for addressing environmental concerns.

These discoveries come at a crucial moment, as this marks the final planned drilling expedition for the foreseeable future, signaling the end of an era with the decommissioning of the JOIDES Resolution. The invaluable insights gained from these samples will allow researchers to refine models of Earth's evolution, enhance predictions of seismic activity and volcanic eruptions, and even aid in the search for life beyond our planet. “Understanding how Earth evolved in the past is essential for understanding its future,” said Poulaki. While the future of scientific ocean drilling may be uncertain, the data collected from this expedition will continue to deepen our understanding of Earth's inner workings for years to come.