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How the Moon was created is a matter of much debate. One of the most prominent theories suggests that a planet the size of Mars collided with the Earth when it was much younger—leading to a lot of debris being created, which eventually led to the creation of the Moon. Now, a new study suggests that pieces of this planet that collided with Earth could be stuck deep within our planet.
Geophysicists in the 1980s made an interesting discovery. It seemed like there were two continent-sized blobs of unusual material deep near the centre of the planet. One under the African continent and one beneath the Pacific Ocean. Each of these “blobs” is twice the size of the Moon and is made of different proportions of elements than the mantle that surrounds them.
The blobs are called large low-velocity provinces (LLVPs) and the next question is where they came from. A study published in the journal Nature on Wednesday suggests that these blobs are what remains of the ancient planet that collided with the Earth billions of years ago, creating the Moon.
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The study also answers another mystery connected with the “giant impact theory” of how the Moon was created. The smaller planet that collided with the Earth was dubbed Theia but no trace of it has been found in the asteroid belt or in meteorites. The researchers believe that most of Theia was absorbed by early Earth, forming these “LLVPs,” with the residual debris from the impact becoming the Moon.
The LLVPs were first discovered when scientists measured seismic waves travelling through the Earth. These waves travel at different speeds through different materials. In the 1980s, studying these seismic waves hinted at large-scale three-dimensional variations deep inside Earth. There seemed to be two structures near the Earth’s core that had an unusually high level of iron.
Researchers from Caltech modelled different scenarios for Theia’s chemical composition and its impact on Earth. Those simulations confirmed that the physics of the collision could have led to the creation of both the LLVPs and the Moon. Some of Theia’s mantle could have fused with Earth’s own, and the other debris from the collision could have mixed together to form the Moon.
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