Mysterious 'Blobs' in Earth's Mantle Might Be the Remnants From the Protoplanet Collision That Birthed the Moon

About 4.5 billion years ago, a protoplanet the size of Mars is believed to have collided with Earth. Now, a new research, published in the journal Nature Climate Change, proposes that remnants from a protoplanet's collision that created the Moon is now residing within Earth's mantle as mysterious blobs.

These enigmatic blobs, known as large low-shear-velocity provinces (LLVPs), are characterized by slower seismic wave movement, indicating differences in temperature or composition. They collectively account for around 4% of the mantle, with one situated beneath Africa and the other beneath the Pacific Ocean.

Theia's Hidden Legacy in Earth's Mantle Revealed

The recent study led by Caltech geophysicist Ojan Yuan explored two massive rock anomalies located deep within Earth's lowermost mantle, nearly 1,800 miles beneath the Earth's surface. These anomalies were identified through seismic observations, as they exhibited slower seismic wave propagation, indicating greater density and compositional distinctions compared to the surrounding mantle.

To investigate the potential presence of Theia's mantle within Earth's lower mantle, the team employed computer simulations. These simulations suggested that a fraction of Theia's mantle, denser by 2 to 3.5 percent compared to the proto-Earth's mantle, could have integrated into the early Earth's lower mantle.

The computer models indicated that these dense Theia remnants could be several tens of miles in width. Over time, this molten rock might have descended, solidified, and formed dense pockets atop Earth's core, representing roughly 1/40th to 1/60th of Earth's total mass.

These findings propose that these rock anomalies would contain a higher iron content than Earth's conventional mantle rock, potentially resembling lunar volcanic rock in chemical composition.

There's a possibility that traces of Theia's remnants could reach Earth's surface through mantle plumes, towering superheated rock formations ascending from the vicinity of Earth's core. Past research suggests regions like Iceland, Hawaii, and the Galapagos formed as tectonic plates drifted over mantle plumes, causing these plumes to interact with overlying materials.

Yuan proposed that evidence of Theia remnants might be transported to surface volcanoes through mantle plumes, suggesting an intriguing link between Earth's geological history and its ancient mysteries.

Giant Impacts Might Explain the Mysterious Blobs

Another recent research, published last month in the journal PNAS, suggested that giant impacts could explain the enigmatic Large Low-Shear-Velocity Provinces (LLVPs) within Earth's mantle. Although the studies didn't specifically pinpoint the moon-forming impact, they explored Earth's complex dynamics.

The study focused on mantle circulation and proposed that valuable elements from ancient cosmic impacts might still reside within LLVPs. These mantle anomalies, as suggested by Yuan and colleagues in their latest study, could potentially contain materials from various ancient impacts during Earth's early history.

The significance of these hidden mantle anomalies, lies in their association with mantle plumes, which are also closely tied to volcanic hotspots, including kimberlite eruptions, known for their diamond-bearing rock formations.

The geochemical composition of these mantle blobs remains a mystery, but volcanic activity offers a window into their nature. Basaltic rocks erupting over these regions may contain traces of magmatic material from the mantle blobs, making them a promising avenue for scientific exploration.

Comparing these volcanic rocks to lunar materials might unveil shared origins, provided samples from the moon's interior can be obtained through future missions, such as the Artemis program.

Yuan expressed hope that "future missions to the moon can test our hypothesis," underscoring the potential for further exploration and gaining insight into Earth's ancient history through lunar missions.