The mysterious masses of rocks as large as continents found hundreds of miles below the crust could be as old as the Earth itself.

Scientists previously thought that these buried continents were from subducted oceanic plates.

Underground Continents

Findings of a new study, however, suggest that these regions of rock may have formed from an ancient magma that solidified at the beginning of our planet's formation.

The study, which was published in the journal Geochemistry, Geophysics, Geosystems on July 31, also suggests that these deep-mantle continents survived the impact that created the moon.

Study researcher Curtis Williams, a geologist at the University of California-Davis, and colleagues traced the origin of volcanic rock samples found across the world back to two solid continents buried deep down the planet's surface.

Igneous Rocks

The researchers looked at geological samples from Hawaii, Iceland, the Balleny Islands in Antarctica, and other regions where hot rocks bubble up from deep down the Earth's surface all the way up.

These samples emerge as lava and become igneous rocks when cooled. They also carry with them ancient isotopes such as the primordial helium-3 created during the Big Bang.

The researchers found that some of the samples had more helium-3, which means they may have come from primitive rocks in the mantle.

Williams and colleagues then used a new model to trace the path of these primitive geological samples from the mantle to the Earth's surface.

As Old As The Earth

The isotope information and the new model shed light on the composition of the two giant masses and how they formed, revealing that these continents have existed as early as 4.5 billion years ago when the Earth was still forming.

"These continent‐sized provinces in Earth's deep interior formed early in Earth's history, survived the violent Moon‐forming giant impact, and remained relatively unmixed with the rest of the solid Earth over the past 4.5 billion years," the researchers wrote in their study.