Scientists have hypothesized that large chunks of matter in the Earth’s mantle (large low shear regions, LLSVPs) could be parts of Theia, the protoplanet that struck the Earth and gave rise to the Moon.
Scientists concluded that the Moon was created when another planet (now called Theia) collided with the very early Earth – chunks of Earth, Theia, or both, that were thrown into space during the collision, eventually merged with the Moon. Theories as to what happened to the rest of Theia are still debated.
In the new work, the Arizona team suggests that much of Theia’s mantle ended up in the Earth’s mantle, forming what are now called large regions of low shear rate, with LLSVPs one underneath the African continent and the other under the Pacific Ocean.
Scientists have studied LLSVP for many years – their existence has been confirmed by studying seismic data around the world. When seismic waves collide with LLSVP, they slow down, which suggests 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. Scientists note that if Theia’s mantle was denser than that of the Earth, any part of it that made its way to the mantle would eventually make its way to the core.
To back up their ideas, scientists built a model that depicts the Earth as it was about 4.5 billion years ago, and then shows what would happen if a planet the size of Mars or even larger collided. The model also suggested that the mantle of the putative planet Theia was rich in iron, making it extremely dense. In their model, Theia finds itself largely destroyed, with pieces thrown into space to create the Moon, and much of its mantle disintegrating into fragments that penetrate the Earth’s mantle. Billions of years later, the fragments coalesce to form LLSVP.
The researchers note that the idea of the Theia fragments that make up LLSVP has already been expressed by others in the field, but suggest that their work is the most complete to date.