Deep within the Earth, two massive structures lie hidden near the molten core. These enormous formations, known as large low-shear-velocity provinces (LLSVPs), might hold clues about an ancient planet that collided with Earth billions of years ago. Initially discovered through seismic wave patterns, these structures reveal a unique composition that differs significantly from the surrounding rock.
A popular theory suggests these blobs are remnants of *Theia*, a hypothetical planet that struck early Earth, leading to the formation of the Moon. If true, these remnants have been embedded in Earth’s mantle for over 4.5 billion years, representing a lost world beneath our feet.
LLSVPs were mapped using seismic tomography, which studies how earthquake waves travel through different materials. As these waves pass through the blobs, they slow down, indicating that these structures are hotter and denser than the surrounding rock. The LLSVP beneath Africa is particularly notable, as it rises 800 to 1,000 kilometers from the core-mantle boundary, comparable to stacking around 90 Mount Everests. Together, the two known LLSVPs may account for 3% to 9% of Earth’s volume—a significant amount hidden deep underground.
A 2021 study in *Nature Communications* supports the idea that these structures could be fragments of Theia. Researchers modeled how denser material from Theia might have mixed with Earth’s mantle after the impact, closely matching the locations and characteristics of the current LLSVPs. This aligns with the giant impact hypothesis, which explains the Moon’s formation through a collision with a Mars-sized object.
Not only do these LLSVPs offer insights into Earth’s history, but they also impact our planet’s surface. Located near the core-mantle boundary, they interact with mantle plumes—hot, buoyant columns of rock responsible for volcanic activity in places like Hawaii and Iceland. A 2020 article in *Progress in Earth and Planetary Science* discussed how these deep structures may persist for billions of years, affecting surface geology through tectonic processes.
Many hot spot volcanoes cluster around the edges of the LLSVPs, with the African blob linked to significant geological changes like continental rifting. This suggests that these ancient formations are not mere geological relics; they actively shape our planet’s surface. However, studying these deep structures is challenging. The Kola Superdeep Borehole, the deepest human-made hole, reached only 12 kilometers—just a fraction of the distance to the core-mantle boundary. Most of what we know about LLSVPs is based on indirect methods, like gravity models and simulations.
Experts continue to explore various theories about these mysterious structures. Some propose they could be accumulated oceanic crust that has been trapped in the mantle. Others suggest they might represent primordial materials from Earth’s earliest days. Nevertheless, the concept of Theia’s remnants provides the most cohesive explanation, supported by seismic readings and material density comparisons. Even *mainstream science outlets* are acknowledging the possibility that beneath Earth’s surface lies more than just rock—there might be the remnants of a lost planet.
The ongoing research into LLSVPs not only reveals Earth’s hidden history but also shapes our understanding of geological processes. As we delve deeper into these ancient mysteries, we may just uncover the secrets of our planet’s formation and evolution.
