Something Is Sucking Iron Out of Earth’s Crust, and Scientists Think They Know What

Are garnet gemstones behind the case of Earth’s missing iron? Credit: Shutterstock
What makes the Red Planet red? The answer, as Sherlock Holmes might say, is elementary. And that element is iron.

By Brandon Specktor |

The continental crust of Mars is so iron-rich that, over billions of years, surface rocks actually rust when exposed to the meager oxygen in the planet’s atmosphere. The result is a rust-coated planet that appears red, even from Earth.

Earth might rust, too, for that matter, if just a fraction more iron was present in the planet’s continental crust. But something, deep underground, is stealing Earth’s iron.

For decades, scientists have pegged the case of the missing iron on a process involving volcanoes, and a mineral called magnetite that sponges up iron from molten magma pools deep underground. Now, a new paper published May 16 in the journal Science Advances points the finger at a new culprit for Earth’s missing iron. The true thief is not magnetite, researchers from Rice University in Texas say, but a sparkly mineral we all know and love: garnet. [Sinister Sparkle: 13 Mysterious & Cursed Gemstones]

„The accepted wisdom is that magnetite pulls iron from the [magma] melt before the melt rises and gets erupted out at continental [volcano] arcs,“ study author Ming Tang, an assistant professor at Rice University, said in a statement. „Iron depletion is most pronounced at continental arcs, where the crust is thick, and much less so in island arcs, where the crust is thin.“

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