A new theory suggests that large blobs of material in the Earth’s mantle are remnants of the protoplanet Theia.

The Giant Impact Hypothesis for the Origin of LLSVPs. Credit: Li et al.

A team of scientists at Arizona State University has proposed that large blobs of material in the Earth’s mantle (the Large Low Shear Velocity Provinces, LLSVPs) may be left on chunks of Theia, a protoplanet that was theorized to have struck. Earth, which resulted in the creation of the moon. The group argued its case at this year’s Lunar and Planetary Science Conference and is awaiting publication in Geophysical Research Letters.

Most space scientists have come to believe that the moon was created when another planet (now called Theia) collided with a very early Earth – pieces of Earth, Theia, or both that were thrown into space during the collision eventually merged into the Moon. Theories about what happened to the rest of Theia are still being debated. In this new effort, the team in Arizona suggests that much of the Theia mantle ended up in the Earth’s mantle, forming what are now called the Great Low Shear Velocity Provinces, LLSVP, one below parts of the African continent and another under the Pacific Ocean. .

Scientists have been studying LLSVPs for many years; its existence has been confirmed by studying seismic readings around the world. When seismic waves strike LLSVPs, they slow down, suggesting that the material they are made of is denser than the rest of the mantle. LLSVPs are very large and rest on the edge of the outer core. The ASU team noted that if Theia’s mantle were denser than Earth’s, anyone who made it to the mantle would eventually reach the core.

To back up their ideas, the ASU team built a model that represents Earth as it was about 4.5 billion years ago and then shows what might have happened if there was a collision with a planet the size of Mars, or even larger. The model also assumed that the mantle of the theorized planet Theia was rich in iron, making it extremely dense. In his model, Theia ends up mostly destroyed, with pieces thrown into space to create the moon, and much of her mantle breaking into fragments, all the way down to Earth’s mantle. Over billions of years, the fragments coalesce and form LLSVPs.

The researchers note that the idea of ​​Theian fragments that make up LLSVPs has been voiced before by others in the field, but they suggest their work is the most comprehensive to date.

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More information:
52nd Lunar and Planetary Science Conference 2021 (LPI Contribution No. 2548) www.hou.usra.edu/meetings/lpsc2021/pdf/1980.pdf

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