Echoes of Ancient Earth Discovered Deep Within the Planet's Mantle

Learning more about ancient Earth can tell us quite a bit about how it first formed. Now, scientists may have uncovered a new clue when it comes to our planet's origins. They've found a previously unexplained isotopic ratio from deep inside Earth that may be a signal from material during a time before Earth collided with another planet-sized body and created the moon.

About 4.5 billion years ago, a massive body collided with our nascent Earth. The resulting debris from this collision spun off into space and eventually formed our moon. The heat created from this collision would have caused the entire planet to melt. And now, it turns out that some ancient part of the Earth that didn't melt may still exist within our planet's mantle.

"The energy released by the impact between Earth and Theia would have been huge, certainly enough to melt the whole planet," said Sujoy Mukhopadhyay, one of the researchers, in a news release. "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."

In order to see whether a piece of ancient Earth could still be located within the mantle, the researchers analyzed the ratios of noble gas isotopes from deep within the mantle and then compared them to isotope ratios closer to the surface. In the end, they found that 3He to 22Ne ratio from the shallow mantle is far higher than that of the deep mantle. The researchers also found additional evidence of the 129-Xenon to 130-Xenon ratio.

"The geochemistry indicates that there are differences between the noble gas isotope ratios in different parts of Earth, and these need to be explained," said Mukhopadhyay in a news release. "The idea that a very disruptive collision of Earth with another planet-sized body, the biggest event in Earth's history, did not completely melt and homogenize Earth challenges some of our notions on planet formation and the energetics 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."

The findings reveal a bit more about our planet's history and could shed light on planet formation in general across the universe.

The findings were presented at the Goldschmidt conference in Sacramento, California.