The scene seemed straight out of a 19th century adventure book. The French geologist Remi Coltat recalls that he left Granada, where he worked at the Andalusian Institute of Earth Sciences, to embark on an epic journey to the Earth’s mantle. The American ship JOIDES Resolution It set sail from Ponta Delgada, in the Portuguese archipelago of the Azores, on April 12, 2023. It stopped in the middle of the North Atlantic and began drilling into the ocean floor, just 800 meters from the lost Citya strange underwater territory where hydrothermal vents have raised ghostly towers. Coltat remembers the “screams of joy” when, in the ship’s machinery, rocks from the Earth’s mantle began to appear non-stop: a column of 1.268 metrosthe largest sample ever obtained. It is, Coltat proclaims, “a window into the development of life” on Earth.
The Dutch geologist Johan Lissenberg He was in charge of the scientists. “One hypothesis for the origin of life is that it depended on reactions between seawater and rocks like the ones we have recovered,” explains Lissenberg, from Cardiff University in the United Kingdom. These reactions transform the mineral olivine – predominant in the upper layer of the Earth’s mantle – into serpentine rocks, in a process called serpentinization. “This releases hydrogen and subsequently compounds such as methane, which create the conditions in which microbial life can thrive,” says Lissenberg. His expedition was the 399th of the International Ocean Discovery Programa 21-country initiative launched a decade ago.
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The Lost City is located in the Atlantis massif, an underwater mountain slightly higher than Mount Teide. The conditions there are extreme: temperatures of over 90 degrees and very alkaline waters, with carbonate towers reaching 60 metres. The Earth’s mantle is at a depth that is inaccessible with current techniques, normally more than 10 kilometres below the Earth’s crust, but in the Atlantis massif it is within reach, thanks to the separation of two tectonic plates. “These are rocks from the mantle that are no longer in the mantle, but that were there recently,” Lissenberg sums up. The historic hole is called U1601C.
The Dutch researcher believes that the 1,268-metre column of rocks, combined with samples of fluids from hydrothermal vents, is “the best window” to study this hypothetical origin of life on Earth. The team’s microbiologists are determining the quantity and type of microbes in the recovered rocks, as well as the depth at which they are found. “We can combine the microbiological findings with those of serpentinization, to understand the factors that control microbial life in rocks derived from the mantle,” says Lissenberg. His results are published this Thursday. in the magazine Science.
Rémi Coltat spent two months on board the JOIDES Resolutiona 143-meter-long research vessel, capable of drilling more than eight kilometers deep. It is like a small floating village, with more than a hundred inhabitants, including scientists, sailors, cooks and other crew members. “The drilling works 24 hours a day. We worked in 12-hour shifts. When we finished, we went to sleep and resumed the task the next day. It was very exciting when something new appeared,” recalls Coltat, who left Granada a few days ago to join the Institute of Earth Sciences in Orleans, France.
French geologist Rémi Coltat during an analysis of rocks from the Earth’s mantle aboard the ‘JOIDES Resolution’.Frieder Klein
Coltat, born 30 years ago in Nancy, recalls that the previous record was obtained with a probe of just 200 meters in mantle rocks, in an expedition led three decades ago by the French geologist Mathilde CannatLast year, scientists aboard the JOIDES Resolution They had never thought they would go that far, not even in their dreams. “It was incredible when we saw that we could drill so well,” recalls Coltat. In Andalusia, precisely, there is one of the largest outcrops of rocks from the Earth’s mantle in the world: the peridotite rocks, composed mainly of olivine, from Sierra Bermeja, in Malaga. These rocks, serpentinized, acquire a striking green color that made the architect Juan de Herrera use them in the 16th century. as ornamental elements in the Royal Monastery of San Lorenzo de El Escorial.
Geologist Juan Manuel García Ruiz, from the Donostia International Physics Center, has just received 10 million euros from the EU to investigate the role of silica – a mineral made up of silicon and oxygen – in the appearance of living beings. In his opinion, the most remarkable thing about the new study is not its possible clues about the origin of life, but that it will help to determine the origin of methane in these environments: whether it comes from bacteria or from serpentinization reactions.
The German researcher Manuel Dominik Menzelfrom the Andalusian Institute of Earth Sciences, reminds us that knowing the upper part of the Earth’s mantle is essential to understand processes such as magmatism and the formation of the continents themselves. Menzel studies how the mantle naturally reacts with water and carbon dioxide (CO₂). When it interacts, it forms minerals and the CO₂ is fixed, a phenomenon that in the future could serve to eliminate this gas from the atmosphere and hide it underground.
Menzel applauds the new work, in which he did not participate. “It is a great success to carry out such a deep survey. I am very surprised that they have seen so much serpentinization, which is the percentage of water that enters the rock of the mantle,” he says. The German geologist points out that in hydrothermal sources there is energy and different chemical compounds, in addition to rocks from the mantle and magmatic rocks from the crust, the so-called gabbro, which has another chemical recipe. “When they mix, there is more potential to produce very diverse conditions that can give rise to life,” he says.
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