The Origin of the Moon and the Mystery of Earth’s Mantle Provinces Finally Solved
A groundbreaking study led by researchers at the California Institute of Technology (Caltech) has provided evidence that the large low-velocity provinces (LLVPs) deep within Earth’s mantle are remnants of Theia, an ancient planet that collided with Earth billions of years ago. This discovery not only sheds light on the origin of the Moon but also answers long-standing questions about the fate of Theia.
The LLVPs were first discovered in the 1980s and were identified as two continent-sized blobs of unusual material located beneath the African continent and the Pacific Ocean. These blobs, twice the size of the Moon, have distinct compositions from the mantle surrounding them. Geophysicists have been baffled by their origin for decades.
However, the recent study published in the journal Nature on November 1 presents compelling evidence that these LLVPs are remnants of the collision between Earth and Theia. The researchers propose that most of Theia was absorbed into the young Earth, forming the LLVPs, while the remaining debris coalesced to form the Moon.
The research team, led by Qian Yuan, a postdoctoral scholar at Caltech, used seismic wave measurements to identify the LLVPs. These waves travel at different speeds through different materials, and the LLVPs caused the waves to slow down due to their high iron content, making them denser than their surroundings.
Yuan had a breakthrough moment during a seminar when he realized that Theia’s iron-rich composition could have transformed into the LLVPs. The team conducted simulations to model the collision between Theia and Earth, confirming that the physics of the collision could have resulted in the formation of both the LLVPs and the Moon.
The study also provides insights into why Theia’s material clumped into distinct blobs instead of mixing with the rest of the forming planet. The simulations revealed that the energy delivered by the impact remained in the upper half of the mantle, leaving the lower mantle cooler. This allowed the iron-rich material from Theia to remain largely intact as it descended to the base of the mantle.
The implications of this discovery are significant. Further research is needed to understand how Theia’s heterogeneous material influenced Earth’s early evolution, such as the onset of subduction and the formation of the first continents. The findings also offer valuable insights into plate tectonics and the origin of the oldest surviving terrestrial minerals.
The study titled “Moon-forming impactor as a source of Earth’s basal mantle anomalies” was authored by Qian Yuan and a team of scientists from Caltech, Arizona State University, Michigan State University, the Chinese Academy of Sciences, the U.S. Geological Survey, NASA, and Durham University. The research received funding from various sources, including the National Science Foundation and the Caltech Center for Comparative Planetary Evolution.
This groundbreaking study finally provides answers to longstanding mysteries in planetary science, unraveling the origin of the Moon and explaining the existence of the enigmatic LLVPs deep within Earth’s mantle.