Rock weathering is slower than previously thought

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Weathering rocks is a critical process for keeping the earth livable. But on a global scale, things are progressing at a much slower pace than expected, in part because many places on Earth are too dry for them. This is clear from the research which was published on Thursday in Sciences.

Rock weathering is also referred to as geothermal. Without this process, the Earth would become uninhabitable in millions of years. Because volcanoes constantly release small amounts of gas, including the greenhouse gas CO₂, in the atmosphere. Without a counter reaction, the carbon dioxide concentration₂ in the atmosphere, and with it the temperature on Earth continues to rise over time. “Earth will become a kind of flower,” says Abe Sluig, professor of paleontology at Utrecht University, who was not involved in the research.

The fact that this did not happen is because of the CO₂ taken from the air. Carbon dioxide dissolves in the atmosphere₂ up in the rain water. Hence, the rain water is somewhat acidic and thus dissolves the rocks. CO₂ into a reaction product that flows into the oceans. Living organisms convert it into carbonates (including calcium carbonate, also known as calcite) and these are deposited on the ocean floor. Will there be more carbon dioxide₂ In the atmosphere and the temperature rises on Earth, the weathering reaction accelerates and more carbon dioxide disappears₂ From the sky to the bottom of the ocean. As it cools, the reaction slows down.

French chemist

The scientific basis for this weathering mechanism was laid down in the mid-19th century by the French chemist Jacques-Joseph Eppelmen. But the question has always been how strongly weathering interacts with changes in temperature. “For a long time, this was only studied in laboratories,” says Susan Brantley, first author of the now-published paper and professor of geosciences at Penn State. The results of these studies varied widely. “Partly because weathering is such a slow process,” Brantley says.

In the current study, Brantley and his colleagues collected a great deal of data, from laboratory studies, but also from field experiments, in different types of soils, on slopes, in different regions. “We’ve researched realistic weathering ourselves for years,” says Brantley.

The results show that outdoor weathering, if it does occur, is faster than in the laboratory. But on a global scale, this translates differently, because there are many places where weathering can’t or is difficult to happen. “Because it’s too dry. Or because the rock is hidden under a layer of soil so thick that water can’t penetrate,” Brantley says. Overall, the researchers concluded that weathering is slower than previously thought.

Holistic approach

Sluijs says he’s “impressed” with the amount of data processed and the study’s comprehensive approach. “Weathering has been studied at all scales, from the laboratory to the regional to the global scale.”

Commenting on the study, Robert Hilton, professor of sedimentary geology at the University of Oxford, wrote that naturally occurring weathering “unfortunately […] Too slow to account for large carbon dioxide excesses₂ It is released every year by the Human Activities Survey.” What can be done is to break up rocks and spread them over large surfaces to stimulate weathering and accelerate carbon dioxide.₂ to remove it from the atmosphere. It is an approach that is being researched in the Netherlands, in particular with the mineral olivine. But Brantley has doubts about it. Because of the huge amounts of carbon dioxide₂ To extract those that are in the air now, you need a lot of crushed rock and huge surfaces. ” According to her, we must first stop emitting greenhouse gases. And secondly, we must try “everything” to reduce carbon dioxide₂ From the atmosphere, such as growing trees, carbon dioxide₂ Extraction and recording from the air with fixtures.

Read about a Dutch trial: Olivine fulfills its promise as a carbon dioxide capture