Iron Vapor in Z-Machine Reveals Clues About the Formation of Earth and the Moon

Scientists may have created the violent conditions of Earth's formation in a device called the Z machine. Now, the findings are revealing a bit more about how iron vaporizes and how this iron rain may have affected the formation of the Earth and moon.

"We care about when iron vaporizes because it is critical to learning how Earth's core grew," said Sarah Stewart, co-author of the new study, in a news release.

In this case, the researchers used the Z-machine for further research. This device is one of the world's most powerful radiation sources, and can recreate conditions that lead to Earth's formation. The scientists subjected iron samples to high shock pressures in the machine, slamming aluminum plates into iron samples at extremely high speeds. In fact, the researchers developed a new shock-wave technique to determine the critical impact conditions needed to vaporize the iron.

So what did they find? It turns out that the shock pressure required to vaporize iron is much lower than expected. This, in turn, means that more iron was vaporized during Earth's formation than previously thought. This may actually alter the way planetary scientists think about planet formation.

"Rather than the iron in the colliding objects sinking directly to Earth's growing core, the iron is vaporized and then spread over the surface within a vapor plume," said Richard Kraus, one of the researchers. "This means that the iron can mix much more easily with the Earth's mantle."

After cooling the vapor would have condensed into an iron rain that then mixed into Earth's still-molten mantle during formation. This also explains why the moon, which had similarly violent collisions, lacks iron-rich material. The moon's reduced gravity could have prevented it from retaining much of the vaporized iron.

The findings are published in the journal Nature Geoscience.

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