Moon-Forming Crash Left A ‘Signal’ In Planet Earth

What physical evidence exists of a huge collision that formed our Moon and nearly blew the Earth apart, about 4.5 billion years ago? This is the leading theory for how the Moon came to be, but given it happened so long ago the physical evidence is scarce.

Readers may recall the story from last week talking about how oxygen in Moon rocks shows evidence of this crash. This week, there’s a new study  from the same conference that focuses on the other side of the puzzle piece: what can we see on planet Earth? Turns out there might be a “signal” showing us the way.

As the theory goes, the colliding body — which some researchers call “Theia” — would have created a cloud of fragments surrounding our planet that eventually coalesced into the Moon.

The new research says that evidence of this collision would have showed up in the mantle, a layer of the Earth’s interior, and could explain a puzzling difference in isotopes (types) of certain elements that was known before.

“The energy released by the impact between the Earth and Theia would have been huge, certainly enough to melt the whole planet,” stated research lead Sujoy Mukhopadhyay, an associate professor at Harvard University.

“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.”

The team said that the impact did not completely stir the mantle, which would explain why the ratio of isotopes of helium and nitrogen inside the shallow part of the mantle is much higher than the deep mantle.

They also analyzed two isotopes of xenon. Scientists know already that the material on the surface has a lower isotope ratio to what is inside, but what is new is comparing these isotopes pointed to an age of the collision: about 100 million years after the Earth formed.

The research was presented today at the Goldschmidt conference in Sacramento, California.

Source: Goldschmidt