The leading explanation for all of these mysteries is known as the giant impact hypothesis. According to this story, when the ...

Beneath the surface of our planet ... mysterious spots in the Earth's mantle may be remnants of the ancient planet Theia, which collided with Earth about 4.5 billion years ago.

We do not know for sure if Theia existed and if it collided with the young proto-Earth, but the evidence is compelling. For one, we are the only rocky planet ... up the lunar surface—and return ...

Whether a planet has plate tectonics is much more complicated than just having a solid surface, though, and might also depend ... or even whether we should be calling it “Theia." Some scientists even ...

Before Earth and the Moon, there were proto-Earth and Theia (a roughly Mars-sized planet). The giant-impact model suggests ... If you look at the lunar surface, it looks pale grey with dark splodges,' ...