GeoSpace reports:

Ancient, distinct, continent-sized regions of rocks, isolated since before the collision that created the Moon 4.5 billion years ago, exist hundreds of miles below the Earth’s crust, offering a window into the building blocks of our planet, according to new research.

The new study in the AGU Journal Geochemistry, Geophysics, Geosystems used models to trace the location and origin of volcanic rock samples found throughout the world back to two solid continents in the deep mantle. The new research suggests the specific giant rock regions have existed for 4.5 billion years, since Earth’s beginning.

Previously, scientists theorized that separated continents in the deep mantle came from subducted oceanic plates. But the new study indicates these distinct regions may have been formed from an ancient magma ocean that solidified during the beginning of Earth’s formation and may have survived the massive Moon-creating impact.

Determining the masses’ origin reveals more details about their evolution and composition, as well as clues about primordial Earth’s history in the early Solar System, according to the study’s authors.

It’s amazing that these regions have survived most of Earth’s volcanic history relatively untouched, said Curtis Williams, a geologist at the University of California, Davis, in Davis, California and lead author of the study. [Continue reading…]