Scientists’ groundbreaking recovery of mantle rock provides new insights into Earth’s volcanic activity, elemental cycles and possibly the origin of life, and represents a significant advance in geoscience.

An international team has begun studying the role of the Earth’s mantle in supporting life on Earth, driving volcanism and influencing global cycles.

Scientists have successfully recovered the first long section of rocks from Earth’s mantle, the layer beneath the Earth’s crust and the planet’s largest component. These rocks are expected to shed light on the mantle’s role in the origin of life on Earth, the volcanic activity that results from the melting of the mantle, and its influence on the global cycles of important elements such as carbon and hydrogen, according to the research team.

The nearly continuous 1,268 meters (4,160 feet) of mantle rock was recovered during the ocean drill ship’s Expedition 399 “Building Blocks of Life, Atlantis Massif” from a “tectonic window,” a section of the seafloor where rock from the mantle has been exposed along the Mid-Atlantic Ridge. JOIDES Resolution in spring 2023.

The core recovery, which began in the early 1960s, was a record-breaking effort led by the International Ocean Discovery Program, an international marine research consortium of more than 20 countries that recovers cores – cylindrical samples of sediment and rock – from the seafloor to study Earth’s history.

The researchers say the rocks recovered from the Earth’s mantle are more similar to those present on the early Earth than to the more common rocks that make up our continents today. Image credit: Professor Johan Lissenberg

Analysis of the recovered rocks

Since then, the expedition team has been compiling an inventory of the recovered mantle rocks to understand their composition, structure and context.

Their results were published in the journal Sciencereveal a longer melting history of the recovered rocks than expected.

Lead author Professor Johan Lissenberg, from Cardiff University’s School of Earth and Environmental Sciences, said: “When we recovered the rocks last year, it was a major achievement in the history of geoscience, but their value lies even more in what the cores of mantle rocks can tell us about the composition and evolution of our planet. Our study begins by examining the composition of the mantle by documenting the mineralogy of the recovered rocks as well as their chemical composition. Our results are different to what we expected. The rocks contain much less of the mineral pyroxene and the rocks have very high concentrations of magnesium, both of which are due to a much higher amount of melting than we would have expected.”

Professor Johan Lissenberg (left) and colleagues analyse cores recovered from a “tectonic window” on the Mid-Atlantic Ridge. Image credit: Lesley Anderson, Exp. 399, JRSO_IODP

This melting occurred when the mantle rose from the deeper parts of the Earth to the surface.

The results of further analyses of this process could have major implications for understanding the formation of magma and the occurrence of volcanism, the researchers claim.

“We also found channels through which melt was transported through the mantle, allowing us to track the fate of magma after it is formed and rises to the Earth’s surface. This is important because it tells us how the mantle melts and feeds volcanoes, particularly those on the seafloor, which are responsible for most of the volcanism on Earth. Access to these mantle rocks will allow us to make the connection between the volcanoes and the actual source of their magma.”

Possible connection to the origin of life

The study also provides initial results on how olivine, a mineral common in mantle rocks, reacts with seawater, leading to a series of chemical reactions that produce hydrogen and other molecules that can support life.

Scientists believe that this could have been one of the fundamental processes in the origin of life on Earth.

Dr. Susan Q Lang, a geology and geophysics scientist at the Woods Hole Oceanographic Institution who co-led the expedition and was part of a team that continued to analyze rock and fluid samples, said: “The rocks that were present on the early Earth bear a greater resemblance to those we recovered during this expedition than to the more common rocks that make up our continents today.”

Expedition 399 “Building Blocks of Life, Atlantic Massif” of the ocean drilling vessel JOIDES Resolution, which recovered 1,268 m of almost continuous mantle rock in spring 2023. Photo credit: Thomas Ronge (Exp. 399, JRSO_IODP)

“Their analysis gives us critical insight into the chemical and physical environments that may have existed in Earth’s early history and that may have provided a consistent source of fuel and favorable conditions for the earliest life forms over geologically long timescales.”

The international team of more than 30 scientists from the JOIDES Resolution expedition will continue its research on the recovered cores to solve a wide range of problems.

Dr Andrew McCaig, Associate Professor in the School of Earth and Environment at the University of Leeds, the main initiator of Expedition 399 and co-lead scientist of the expedition, added: “Everyone involved in Expedition 399 since it was first proposed in 2018 can be proud of the achievements documented in this paper. Our new deep borehole will be a model for disciplines as diverse as mantle melting processes, chemical exchange between rock and ocean, organic geochemistry and microbiology for decades to come. All data from the expedition will be fully available, a model of how international science should be done.”

Reference: “A long section of serpentinized, depleted mantle peridotite” by C. Johan Lissenberg, Andrew M. McCaig, Susan Q. Lang, Peter Blum, Natsue Abe, William J. Brazelton, Rémi Coltat, Jeremy R. Deans, Kristin L. Dickerson, Marguerite Godard, Barbara E. John, Frieder Klein, Rebecca Kuehn, Kuan-Yu Lin, Haiyang Liu, Ethan L. Lopes, Toshio Nozaka, Andrew J. Parsons, Vamdev Pathak, Mark K. Reagan, Jordyn A. Robare, Ivan P. Savov, Esther M. Schwarzenbach, Olivier J. Sissmann, Gordon Southam, Fengping Wang, C. Geoffrey Wheat, Lesley Anderson and Sarah Treadwell, 8 August 2024, Science.
DOI: 10.1126/science.adp1058