Isotopic ratio from deep within the Earth could reveal echoes of a time before an ancient collision in which the Earth may have collided with a larger planet, creating the moon.
The theory suggests the moon was formed 4.5 billion years ago when the Earth collided with a Mars-sized object dubbed Theia, a European Association of Geochemistry news release reported.
In this event the heat created by the collision would have melted the planet, allowing some debris to fly off and form the moon.
The researchers believe they have identified evidence that the Earth melted billions of years ago, and a part of that ancient Earth is still buried deep within.
"The energy released by the impact between the Earth and Theia would have been huge, certainly enough to melt the whole planet. 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," lead researcher Associate Professor Sujoy Mukhopadhyay of Harvard University said in the news release.
The researchers compared noble gas isotopes from deep within the Earth with those closer to the surface. They found the 3He to 22Ne ratio from the shallow mantle is higher than It is in the deep mantle.
"This implies that the last giant impact did not completely mix the mantle and there was not a whole mantle magma ocean," Mukhopadhyay said.
The researchers also looked at the 129-Xenon to 130-Xenon, ratio which has a lower ratio near the surface.
"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. The idea that a very disruptive collision 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 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," Mukhopadhyay said.
