Macquarie University scientist Dr. A recent study by Chunfei Chen sheds new light on geological processes three billion years ago and marks a major shift in the scientific community’s understanding of early Earth. Recently published in a magazine Nature The research examines the transformative effect of Earth’s gradual cooling on the deep cycle of carbon and chlorine between Earth’s surface and its interior.
Dr. “The cooling of the Earth caused major changes in the deep cycles of both carbon and chlorine,” says Chen.
“Today, chlorine often returns to the surface as volcanic gases, while most of the carbon is retained as solid carbonate hundreds of kilometers deep; but until the earth reached about two-thirds of its present age, the situation was the opposite.’
Magma dominated Earth’s surface soon after the planet formed, but as the planet slowly cooled, crustal plates about 100 km thick formed on the surface and slipped through the mantle in the process of plate tectonics. As oceanic tectonic plates sink back into the mantle at subduction zones, sediments found in trenches beneath the oceans may have also been pushed into the mantle.
Scientists examining the fate of these sediments in high-pressure melting experiments had previously averaged all ocean sediments, where carbon was only a minor component. However, most of the carbon is stored in carbonate deposits – famous examples of large carbonate deposits on the surface include the White Cliffs of Dover or the Dolomites in Italy – and these may behave differently from small bits of carbon.
Dr. Chen’s team used high-pressure experiments to model the sinking of limestones and chalks and found that any dirt in the limestones melted first to form a silicate melt, while carbonate in the solid state was pushed deeper and could travel deeper. cloth. .
The research team also tested conditions that mimicked earlier, warmer periods in Earth’s long history and found that the limestones melted, but the salts did not dissolve in the carbonate melts they created, but instead were pushed deeper into the mantle instead of returning to Earth. surface. . as they are today.
The second author of the study, who analyzed samples at the Australian National University, Dr. “It was surprising to see how the salt and impurities were completely separated from the carbonates,” said Michael Forster.
Dr Forster says the team made a breakthrough when an electron microscope magnified and analyzed small experimental stages, revealing a pile of tempered glass and salt alongside crystals of pure calcite. Seeing this, Chunfei excitedly replied: “Wow, that’s very interesting, this means that the subduction zones must act as a giant filter that allows salt to penetrate deep into the Earth!”
The research is part of a larger project led by Distinguished Professor Stephen Foley of Macquarie University’s School of Life Sciences to trace deep cycles of carbon, nitrogen and chlorine throughout Earth’s evolutionary history.
“The exchange of volatile elements such as carbon, chlorine and nitrogen between the Earth’s deep mantle and its surface is a key factor in the evolution of the climate, oceans and all life on Earth,” says Professor Foley.
“This important study is the first to consider the subduction of large amounts of carbonate sediments rather than medium-sized sedimentary rocks, but it is more realistic that large carbonate blocks are involved in plate tectonics,” he says. “These changes in the behavior of chlorine and carbon over time likely affected how salty seawater was at different times in Earth’s history and influenced the evolution of life on Earth.”
He adds that this research will lead to a more comprehensive view of our planet’s evolution and its delicate interactions with the development of life, and could help us understand conditions on other planets such as Mars. Source
Source: Port Altele
