These continent-sized clumps, known as large low-shear-velocity provinces (LLVPs), have puzzled geologists since their discovery in the 1980s. Seismic waves travel unusually slowly through these structures, which are located about 1,800 miles below the surface, one beneath Africa and the other under the Pacific Ocean. These fragments account for about 4% of the mantle’s mass. The LLVPs are significantly hotter and denser than the surrounding mantle rock, but their origins have remained elusive until now.
The new research, published in the journal Nature, suggests that these LLVPs are the “buried relics” of the Theia collision, which have been hiding near the heart of our planet ever since. This collision not only gave birth to the Moon but may have also contributed to Earth’s unique ability to host life. The hypothesis was first considered during a class discussion on the mystery of Theia’s impact, leading to a collaboration between experts in space and geology.
Simulations developed by the research team illustrate how chunks of Theia’s mantle, tens of miles wide, could have swirled inside Earth’s lower mantle during the impact. As the mostly molten material from Theia cooled and solidified, its high iron content caused it to sink to the border of Earth’s mantle and core. Over time, this material accumulated into the two separate LLVPs, each now larger than the Moon.
While testing a theory based on events so ancient and deep beneath Earth’s surface is incredibly challenging, the researchers believe their model is plausible. The idea that the LLVPs are remnants of Theia has been considered before, but this study is the first to take the notion seriously and provide a comprehensive case for it.
The implications of this finding are significant. The Theia collision, believed to be Earth’s last major accretion event, altered the planet’s composition in just 24 hours. The remnants of Theia, preserved deep within Earth, may still be influencing important geological processes today.
This research adds weight to the Giant Impact Hypothesis for the Moon’s formation and offers a credible explanation for the anomalies at the core-mantle boundary.
Christian Schroeder, an expert in both Earth science and planetary exploration at Scotland’s University of Stirling, told AFP the theory “fits several strands of evidence”. “It is a very significant and exciting finding,” said Schroeder, who was not involved in the research.
He, however, emphasised that the mystery of the Moon’s formation had not yet been solved.
(With inputs from agencies)