The remains of the great impact that created the Moon would be inside the Earth

Scientists have been trying to unravel the enigma of the Moon’s formation for decades. The most accepted theory is that of the ‘great impact’, which maintains that 4.5 billion years ago, when the Earth was finishing forming, there was a collision with the embryo of another planet the size of Mars known as Theia. The ejected material would have ended up being reunited to give rise to the Earth satellite. An international team of scientists believes that remains of that collision also remained inside our planet. “The giant impact that formed the Moon seems to be the origin of the heterogeneity of the early mantle and marks the starting point of the geological evolution of the Earth,” explains one of the authors of the work, published this Wednesday in the journal ‘Nature‘.

These would be two enormous masses located 2,900 kilometers deep, just below West Africa and the Pacific Ocean. They are what geologists call ‘large low velocity provinces’ (LLVP). One of the keys that support this origin is its behavior when there is an earthquake. Seismic waves significantly reduce their speed, which would imply that their composition is denser than the rest of the Earth’s mantle – between 2% and 3.5% -, similar to that of lunar rocks and enriched with iron. At the time of impact, these heavier fragments of Theia would have descended and been preserved to the present day.

“A crazy but possible idea”

Until this “crazy but possible idea” was initially proposed in March 2021, specialists had made thousands of simulations of that enormous impact. Most suggested that the Moon inherited its material from Theia, which then fell apart and its remains would end up scattered. Meanwhile, there wouldn’t have been too many left on Earth. Thanks to a new computational fluid dynamics method called ‘Meshless Finite Mass’ (MFM), they have discovered that the early Earth’s mantle was divided into different strata, with an upper and lower mantle of very different compositions. The first was a magma ocean created from a mixture of material from Earth and Theia; the second would be solid and would preserve the original terrestrial composition, hardly being altered by that shock.

This heterogeneity suggests that the bowels of our planet are far from being a uniform and “boring” system, according to the researchers. In fact, they could rise to the surface in events like those that formed the volcanic islands of Iceland and Hawaii. The research not only contributes to a better understanding of the internal structure of the Earth, but also its long-term evolution and the formation of the inner solar system. And even more. “It provides inspiration for understanding the formation and habitability of exoplanets beyond our solar system,” they conclude.

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