I was a bit mind-boggled to read this article.
Scientists seeking to explain a series of seemingly inexplicable formations deep within the Earth’s surface may have found an explanation: They came from outer space.
Researchers with Arizona State University’s School of Earth and Space Exploration said in a recently published paper that the “continent-sized Large Low Shear Velocity provinces” identified in Earth’s mantle—essentially giant formations of rock the origins of which scientists have struggled for decades to explain—may have been formed by Theia, the proto-planet thought to have slammed into the ancient Earth billions of years ago.
The collision between Earth and Theia is hypothesized to have ejected a significant portion of Earth into outer space; those fragments would have eventually coalesced under Earth’s gravity to form the Moon.
There's more at the link.
I'm no geologist, but given the temperatures in and beneath the earth's mantle, I'd assumed that any bits and pieces of another planet would long since have melted and combined with Earth's own planetary material in an unidentifiable slag. Looks like I was wrong.
The thought that we may be standing (at a few miles' remove, of course) on the remains of another planet, one that formed our Moon out of the ejecta caused by its collision with Earth, is . . . somehow surreal.