The collision with a celestial body called Theia 4.5 billion years ago left behind remains deep inside the Earth – and also created the Moon.

For decades, scientists have been puzzled by two major mysterious spots in the Earth’s crust. These rock formations are thousands of kilometers long and slightly denser than their surroundings, suggesting they are made of different materials than the rest of the mantle. New computer models support a dramatic origin story for these strange blobs: They are artifacts of a giant collision 4.5 billion years ago between early Earth and a planet. another young star – similar collision formed the Moon1. Modeling shows that this violent encounter caused material from the colliding world, known as Theia, to become embedded in the lower half of Earth’s mantle. The collision also caused some of Theia’s remains to be sent into orbit; these eventually merged to form the Moon. Robin Canup, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, said the idea that mantle anomalies are remnants of Theia is not new. “But in my view, this is the first article that really takes this perspective seriously,” she said.

The study appears today in the journal Nature. Cosmic collision A giant collision between the young Earth and a smaller protoplanet has long been the dominant theory about the formation of the Moon. Such an origin would explain features such as the absence of many volatile compounds on the Moon, which would have been vaporized during its impact with Earth. Such a huge impact in the early stages of Earth’s development should have left its mark. Yuan and his colleagues wondered whether these traces might include exotic regions of the Earth’s mantle – the layer between the crust and core. Scientists call these formations low-velocity protrusions because seismic waves travel through them more slowly than the rest of the mantle.

Researchers performed computer simulations of the interaction between Theia’s mantle and Earth from the time of the collision until now. This suggests that some of Theia’s material initially flowed into the lower part of Earth’s mantle, and that most of Theia’s material accumulated there over time, forming blobs. The authors reported these results at the 2021 planetary science meeting.

For their latest work, the authors expanded their model. They discovered that the energy from the planetary collision would partially melt the Earth’s crust, which would then have two layers: a molten upper part and an essentially solid lower part. The upper molten layer will sweep some of Theia’s material into Earth’s material. But other material from the protoplanet would have flowed through the molten part of the mantle and become trapped in the layer below. Eventually, Theia’s remains will form two separate blobs. During this time, even more material was launched into orbit and formed the Moon. Compare the mantle and the Moon The model is not definitive proof that the mantle anomalies are remnants of Theia, but Yuan and his colleagues have “argued that [the scenario] can be taken seriously.” “, Canup said. “It wasn’t just a throwaway idea, but I think [it] existed before this work.” The next step will be to confirm the models by comparing mantle rock samples with samples from the Moon.

Compare the mantle and the Moon The model is not definitive proof that the mantle anomalies are remnants of Theia, but Yuan and his colleagues have “argued that [the scenario] can be taken seriously.” “, Canup said. “It wasn’t just a throwaway idea, but I think [it] existed before this work.” The next step will be to confirm the models by comparing mantle rock samples with samples from the Moon. Maxim Ballmer, a geodynamicist at University College London, is not sure this idea of ​​mantle anomalies will hold. Ballmer says the model “definitely needs to be tested.” “But I think it’s an idea worth pursuing.” Yuan hopes this and subsequent research can shed light on what makes Earth so unique – factors that may include the collision with Theia. This study suggests that “this giant impact created heterogeneity on Earth that could persist for billions of years,” he said. doi: https://doi.org/10.1038/d41586-023-03385-9