Two giant blobs lurk deep within the Earth, but why?

The mysteries of Earth's deep interior have long fascinated scientists, and recent research has shed new light on the enigmatic presence of two massive blobs lurking within the planet. These blobs, known as large low-velocity provinces (LLVPs), reside deep beneath the Earth's surface, one beneath the Pacific Ocean and the other beneath the African continent. They are colossal in scale, each roughly twice the size of the moon and possessing material composition different from the surrounding mantle.

A groundbreaking study, detailed in the journal Geophysical Research Letters, suggests a captivating origin story for these LLVPs. It traces their existence back to a cataclysmic event around 4.5 billion years ago, when a celestial body comparable in size to Mars collided with Earth. This colossal impact not only gave birth to the moon but also left behind remnants of the colliding body within the Earth itself, forming the LLVPs.

According to this theory, proposed in a 2023 paper in Nature, the colliding body, dubbed "Theia," was largely absorbed by Earth, with its remnants accumulating at the core-mantle boundary to form the LLVPs. This revelation challenges previous assumptions that any remnants of Theia within Earth would have been thoroughly mixed over billions of years of geological activity.

Furthermore, the study suggests that these LLVPs played a pivotal role in shaping Earth's geological dynamics. Around 200 million years after the collision, they are believed to have generated intense heat plumes within Earth, disrupting the surface and initiating processes like subduction, where tectonic plates sink beneath one another. This mechanism may explain the presence of ancient minerals like zircon crystals, hinting at subduction events over 4 billion years ago, crucial for the development of plate tectonics.

However, while this hypothesis offers intriguing insights, it also raises significant questions and debates within the scientific community. Some geologists question whether the collision would have led to a complete recycling of Earth's crust instead of the development of plate tectonics, similar to the fate of Venus. Additionally, there are geochemical inconsistencies that challenge the collision theory's validity.

Nevertheless, the significance of plate tectonics in Earth's geological and biological history cannot be overstated. While it can be destructive, plate tectonics facilitate vital processes like the carbon cycle, crucial for sustaining life on Earth. However, recent studies suggest that mobile plate tectonics may not have been present during the emergence of life on Earth, sparking discussions about the conditions necessary for life on other planets.

Ultimately, the quest to unravel Earth's geological mysteries and understand the role of plate tectonics in shaping our planet's history and fostering life remains ongoing, promising further discoveries and insights into our planet's complex and dynamic nature.