Unveiling the Ancient Origins of Earth and the Moon: Impact of an Ancient Planet

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In a groundbreaking discovery, researchers from Caltech have shed light on the origins of Earth and its celestial companion, the Moon. Their findings, published in the journal Nature, propose that large low-velocity provinces (LLVPs), massive continent-sized blobs of unique material deep within Earth, are remnants of an ancient planet that collided with our young Earth billions of years ago, leading to the formation of the Moon.


The journey to this revelation began in the 1980s when geophysicists identified these enigmatic LLVPs while studying seismic waves within the Earth. These peculiar structures, found near the Earth’s core, had higher iron content, making them denser and causing seismic waves to slow down as they passed through.


Led by Qian Yuan, a postdoctoral scholar research associate at Caltech, the team connected the dots between the Moon’s iron-rich composition and the LLVPs, thanks to a theory proposed by Professor Mikhail Zolotov from Arizona State University. This theory suggested that an ancient planet, known as Theia, collided with Earth, ultimately forming the Moon.


Through extensive simulations and collaborations, the researchers demonstrated that the Earth-Theia collision gave rise to both the LLVPs and the Moon. Some of Theia’s mantle merged with Earth’s, forming the LLVPs, while debris from the collision coalesced to create the Moon. This also explains the absence of Theia’s traces in the asteroid belt or meteorites, as most of its material was absorbed into Earth.


But why did Theia’s material form distinct blobs instead of blending with Earth? The team’s simulations revealed that the energy from the impact remained in the upper half of Earth’s mantle, resulting in a relatively cooler lower mantle. This lower temperature allowed Theia’s iron-rich material to remain relatively intact and sink to the base of the mantle.


This discovery not only unravels the mystery of Earth’s LLVPs but also offers insights into Earth’s early evolution, including the onset of plate tectonics, the formation of continents, and the origin of the oldest terrestrial minerals. As Paul Asimow, the McMillan Professor of Geology and Geochemistry at Caltech, notes, “Investigating their consequences for Earth’s earliest evolution will shed light on pivotal events such as the emergence of subduction and the formation of the oldest terrestrial minerals.”


This study provides a captivating glimpse into the violent history that shaped our planet and brought the Moon into existence, expanding our understanding of the cosmos and the intricate connections that bind celestial bodies in our vast universe.

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