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New Study: Iron Rain may Explain Earth-Moon Differences

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New Study: Iron Rain may Explain Earth-Moon Differences

Not much is known about Earth’s “inner space” —its core — although scientists agree on one thing. Much of the core consists of iron. But just how much iron is there remains the subject of debate. Now, new research show that the asteroids that slammed into Earth and the moon more than 4 billion years ago were vaporised into a mist of iron.

This new research suggest that the iron mist thrown up from the high velocity impacts of these asteroids travelled fast enough to escape the moon’s gravity, but stayed gravitationally stuck on more massive Earth. And these results may help explain why the chemistry of the Earth and the moon differ.

Scientists from Lawrence Livermore National Laboratory, Sandia National Laboratory, Harvard University and the University of California at Davis used the Sandia National Laboratories Z-machine to replicate conditions that existed when the Earth was first formed.

This artist’s illustration shows a planetary scale impact on the Moon. Illustration by W.K. Hartmann. Read more at:

This artist’s illustration shows a planetary scale impact on the Moon. Illustration by W.K. Hartmann.

The researchers found that the minimum pressure needed to vaporize iron is much lower than previously thought. The lower energy needed to vaporize iron resulted in an iron rain created on the Earth’s surface that penetrated the molten layers of the Earth. The heavier iron particles eventually collected at the center of the Earth forming the molten iron core that exists today.

“This causes a shift in how we think about processes like the formation of Earth’s iron core,” Richard Kraus scientist at Lawrence Livermore National Laboratory (LLNL) said. “Rather than the iron in the colliding objects sinking down directly to the Earth’s growing core, the iron is vaporized and spread over the surface within a vapor plume. After cooling, the vapor would have condensed into an iron rain that mixed into the Earth’s still-molten mantle.”

“The timing of Earth’s core formation can only be determined via chemical signatures in Earth’s mantle, a technique that requires assumptions about how well the iron is mixed. This new information actually changes our estimates for the timing of when Earth’s core was formed,” Kraus added.

The results could imply that models for estimating the time scales of Earth’s core formation could be out by as much as a factor of ten, with the core forming much earlier in Earth’s history than previously recognized.

To the Moon

This process may also explain why the Moon, which is thought to have formed by this time, lacks iron-rich material despite being exposed to similarly violent collisions. The authors suggest the Moon’s reduced gravity could have prevented it from retaining most of the vaporized iron.



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