Large parts of the Earth's insides might originally have belonged to another planet, scientists say.
Part of a hypothesised planet named Theia is located beneath Africa, they say, and another beneath the Pacific Ocean.
The evidence is the existence of 'large low-shear-velocity provinces' of lava (LLSVPs) in the Earth's mantle, which is between the crust - which we live on - and the outer core of the planet.
When seismic waves hit the LLSVPs they slow down, suggesting they're made of something different to the rest of the mantle.
"Theia's mantle may be several percent intrinsically denser than Earth's mantle, which enables the Theia mantle materials to sink to the Earth's lowermost mantle and accumulate into thermochemical piles that may cause the seismically-observed LLSVPs," a new study, published in Geophysical Research Letters, says.
But how did it get there? The clue is something we see in the skies most nights - the moon.
Most scientists studying the Earth's distant past now believe it was struck by another planet - Theia - about $4.5 billion years ago. At the time, the Earth had no moon. The resulting explosion flung material into space, which formed the moon.
"The 'giant impact hypothesis' is one of the most examined model for the formation of moon, but direct evidence indicating the existence of the impactor Theia remains elusive," the study reads.
"Simulations of the giant impact suggest that at least some intact pieces of Theia's mantle may have persisted in the Earth's mantle throughout Earth's history."
Previous research has suggested Theia was about the size of Mars, which would have been how big Earth was at the time. It's also been suggested Theia is where most of our water comes from too.