This discovery explains why our planet's mantle packs a heck lot of this chemical compound, scientists argue

Mar 19, 2015 08:22 GMT  ·  By

Iron-rich rains birthed by celestial bodies crashing into our planet fell on Earth billions of years ago, scientists at Sandia National Laboratories and fellow researchers argue in a recent paper in the journal Nature Geosciences.

In the aftermath of these extreme weather events, our planet's mantle, which measures nearly 2,000 miles (roughly 3,200 kilometers) in thickness, ended up packing a heck lot of this chemical compound.

How cosmic collisions birth iron rains

Scientists have not yet had the chance to actually see a planet forming before their very eyes, simply because such processes take eons and the average human lifespan is, well, way less than that.

However, based on what they have until now learned about our Solar System and the cosmos, they theorize that celestial bodies like Earth and its neighbors form from debris that binds together first as rocks and then as so-called planetesimals, which are essentially baby planets.

Writing in the journal Nature Geosciences, the Sandia National Laboratories researchers and colleagues argue that, shortly after it came into being, Earth was bombarded by an army of such planetesimals.

Having carried out a series of experiments in laboratory conditions, the scientists found that, rather than plow through Earth's upper layers and stop when reaching the core, these celestial bodies that crashed into our planet billions of years ago likely disintegrated on impact.

The force of these collisions was enough to vaporize the blocks of iron in the planetesimals. The resulting clouds blanketed the planet, and eventually, the iron fell to the ground in the form of rain.

“The iron was vaporized, spread out in a plume over the surface of the Earth and rained out as small droplets. The small iron droplets mixed easily with the mantle,” researcher Rick Kraus with the Lawrence Livermore National Laboratory said in a statement.

The same thing happened to the Moon

Just like Earth, the Moon got hit by plenty of celestial bodies while still young. Of these, some packed considerable amounts of iron that, after colliding into its surface, caused metal rains.

What's interesting is that, although it too had iron rain on its surface in its early years, the Moon is by no means iron-rich. At least not when compared to our planet.

Researchers believe this is because, since the Moon's gravitational pull is not as strong as Earth's, whatever iron vapors were produced when planetesimals collided with it simply drifted away.

Earth, however, kept the iron vapors close to its surface and thus made it possible for the metal rains that ultimately altered its makeup to happen.

Earth's core and mantle contain a lot of iron
Earth's core and mantle contain a lot of iron

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Artist's impression of a cosmic collision
Earth's core and mantle contain a lot of iron
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