Relics of Theorized Huge Primordial Collision Reside in Earth’s Deep Interior

A view of Earth by the Apollo 17 crew travelling toward the moon on Dec. 7, 1972. NASA/Handout/Reuters

WASHINGTON—Seismologists have recognized 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 hypothesized to have spawned the moon—the collision between primordial Earth and a Mars-sized object called Theia, researchers said on Wednesday.