Shortly after the formation of our solar system, 4.6 billion years ago, the Mars-sized celestial body Theia collided with the primordial Earth. Our moon was formed from the debris thrown into space – a mixture of matter from Theia and primordial Earth. But remains of Theia are also preserved deep in the Earth’s mantle, researchers have now discovered.
Two previously mysterious areas of increased density can be explained as accumulations of Theia matter, the scientists from Great Britain and the US write in the journal ‘Nature’. “Seismic studies of the Earth’s interior reveal two continent-sized regions in which seismic waves propagate unusually slowly,” explain Qian Yuan of Arizona State University and his colleagues. The areas deep in the Earth’s mantle therefore differ in composition from the surrounding material of the Earth’s mantle and are two to three and a half percent denser.
Anomalies deep in the Earth’s mantle beneath the Pacific Ocean
Until now, there has been no generally accepted scientific explanation for these regions. Using extensive computer simulations, Yuan and his colleagues now show that such denser regions are a natural consequence of large collisions during planet formation – and that the two anomalies, located deep in the Earth’s mantle beneath the Pacific Ocean and beneath Africa, could be remnants . about Theia. “Our collision simulations show that part of Theia’s mantle can migrate into Earth’s lower mantle,” the researchers said.
Based on the composition of the moon, which was formed from soil and Theia debris, Yuan and his colleagues obtain a density for these sinking fragments of the Theia mantle that is two to three and a half percent higher than that of Earth’s normal mantle – in good agreement with the result values derived from seismic studies. As the team’s simulations also show, these are fragments of the Theia mantle up to fifty kilometers in size that have sunk into the Earth’s interior and coalesced into larger structures above the Earth’s core.
Theory could explain oddities in Hawaii
An important aspect is that these larger compactions in the Earth’s mantle can remain stable for four and a half billion years, until today, as the computer models show. And there’s another piece of evidence that supports Yuan and his colleagues’ hypothesis: The Hawaiian Islands contain a form of volcanic basalt whose composition is surprisingly similar to the rock of the moon’s lava plains. This rock may have come from the region of Theia matter, deep beneath Hawaii.
But Yuan and his colleagues’ model is not only important for the Earth-moon system. “Major collisions often occur in the final phase of planet formation,” the researchers emphasize. “Similar inhomogeneities are therefore likely to exist in the interiors of other planets.” And there may even be traces of even earlier collisions within the Earth.
Source: Krone
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