Imagine Earth containing the remnants of an ancient planet locked within its mantle. This intriguing concept has gained momentum with recently emerging seismic research showing two gigantic structures below Africa and the Pacific Ocean, giant low-velocity provinces (LLVPs). These massive structures, as big as continents, have puzzled researchers for decades since they possess peculiar seismic properties. They slow down seismic waves, signifying a distinct constitution from the immediate surroundings of the mantle. A fresh hypothesis now emerges to state that the LLVPs are the remains of a protoplanet named Theia, which collided with Earth more than three billion years ago.
The collision of Earth with Theia is a cornerstone element of the giant-impact hypothesis, which makes predictions about the origin of the Moon. Theory previously had left Theia’s fate itself unknown. New findings by researchers from Caltech and Arizona State University suggest that Theia’s mantle material was drawn into the Earth’s mantle, forming the LLVPs. These denser-than-viron structures may have fallen to the lower mantle, remaining whole for billions of years. “The moon appears to have materials within it representative of both the pre-impact Earth and Theia,” said Steven Desch of ASU’s School of Earth and Space Exploration. This is a new perspective on the early history of Earth and planetary formation processes.
The LLVPs, which were found in the 1980s through seismic imaging, contain a high level of iron, making them denser and slowing down seismic waves. This singular property has been the subject of scientists’ speculations regarding their origin. This new study employs advanced simulations to model the collision of Earth and Theia and demonstrates that the impact energy was concentrated at the top of the mantle. This chilled the lower mantle, preserving the iron-rich material of Theia intact to form the LLVPs. “Through mantle convection simulations, we found that the dense, iron-rich materials from Theia could sink to and accumulate at the base of Earth’s mantle,” explained Mingming Li at ASU.
These findings do not just unlock secrets about Earth’s history but also have implications for other bodies in the universe. If the remnants of Theia comprised the LLVPs, it is possible that others may exist in planets that have been subjected to major impacts. Unscrambling such structures would enhance knowledge on the evolution of the planet, tectonics, and continental building. Studies also suggest reevaluation of the part played by the LLVPs in the Earth’s geodynamic evolution. If indeed they are the leftovers of Theia, then they may have influenced processes like plate tectonics and the Earth’s magnetic field.
The research highlights the importance of interdisciplinary collaboration in deciphering complex geological events. It is through the combination of geophysics, geochemistry, and advanced modeling that researchers have been able to develop a plausible reason for the existence of LLVPs. “A logical consequence of the idea that the LLVPs are remnants of Theia is that they are very ancient,” explained Paul Asimow of Caltech. This highlights the necessity of investigating their role in Earth’s early development, such as the initiation of subduction and the genesis of the first continents.
The presence of the LLVPs under our feet is a testament to the interconnectedness of terrestrial processes. From the blazing origins of our Moon to the hidden realms of our world, these features give us a glimpse into the cosmic forces that shaped our Earth. While we pursue further investigation of the interior of Earth, the LLVPs are silent witnesses to when a very old collision irreversibly altered the planet. Their work not only enhances our understanding of the history of the Earth but also unveils new areas of investigation into the mystery of planet formation and evolution.
