Billions of years ago, our ancient planet collided with Theia, releasing tremendous amounts of energy believed to have produced a whole mantle magma ocean. Following the impact, the Earth and moon formed. Now, scientists believe stories of the ancient past still ripple in the Earth’s mantle.
“The energy released by the impact between the Earth and Theia would have been huge, certainly enough to melt the whole planet,” says Associate Professor Sujoy Mukhopadhyay of Harvard. “But we believe that the impact energy was not evenly distributed throughout the ancient Earth. This means that a major part of the impacted hemisphere would probably have been completely vaporized, but the opposite hemisphere would have been partly shielded, and would not have undergone complete melting.”
To reach this conclusion, researchers analyzed the ratios of noble isotopes taken from within the Earth’s mantle, comparing them with those collected nearer to the surface. According to ZME Science, “They found that 3He to 22Ne ratio from the shallow mantle is significantly higher than the equivalent ratio in the deep mantle. Analysis of the 129-Xenon to 130-Xenon ratio came out similarly. If the 4.5 billion-year-old Theia impact had completely melted ancient Earth, then we should have seen a more evenly mixed mantle.”
“The geochemistry indicates that there are differences between the noble gas isotope ratios in different parts of the Earth, and these need to be explained,” Mukhopadhyay continued.”The idea that very disruptive collisions of the Earth with another planet-sized body, the biggest event in Earth’s geological history, did not completely melt and homogenize the Earth challenges some of our notions on planet formation and the energetic of giant impacts. If the theory is proven correct, then we may be seeing echoes of the ancient Earth, from a time before the collision.”
“This exciting result is adding to the observational evidence that important aspects of Earth’s composition were established during the violent creation of the planet and is providing a new look at the physical processes by which this can occur,” says Professor Richard Carlson, former President of the Geochemical Society.