Relics of huge primordial collision reside in Earth's deep interior

Seismologists have recognised since the 1970s that two mysterious continent-sized blobs reside in the deepest part of Earth's mantle, one under Africa and the other under the South Pacific region. These blobs, denser than the material surrounding them, may be relics from a cataclysm early in our planet's history hypothesised to have spawned the moon - the collision between primordial Earth and a Mars-sized object called Theia, researchers said on Wednesday. The researchers ran computer simulations examining the impact event, geophysical properties of the material that likely made up Theia and the evolution of Earth's mantle - the broadest of the layers that comprise our planet's interior structure at about 1,800 miles thick. "It is incredible because we can uncover relics of another planet - Theia - if we dig deep enough in Earth's mantle," added planetary scientist and study co-author Hongping Deng of the Chinese Academy of Sciences' Shanghai Astronomical Observatory. "After the impact, these impactor materials would sink down to the core-mantle boundary because they likely have higher density than ambient mantle, and it is the extra density that allows them to survive Earth's whole history," Yuan said.