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Missing Chromium: Inside Earth’s Crust

The Earth is made up of plenty of elements but Chromium is uncommon. This has scientists puzzled.

chromium element

Photo: p.Gordon (Flickr)

A piece of Chromium.

The Earth is made up of plenty of elements, the most abundant ones being iron, oxygen, silicon, magnesium, and sulfur.

Chromium is uncommon, but more uncommon than expected. This has scientists puzzled.

Where Did The Chromium Go?

Chromium was first discovered in 1797 by the French chemist Louis Nicolas Vauquelin. Chromium turns colors when combined with other elements. It’s what makes emeralds green and rubies red. Even though it breaks easily, it can be polished to a bright shine and is used cover metals and make stainless steel.

Scientists can compare elements found in four and half billion year old meteorites and the Earth’s crust to give them clues about how the Earth was formed when our solar system was young. They know that meteorites contain more chromium than the Earth. The question is why?

Following The Clues

The missing chromium had only two places to go when the Earth was forming. Either it evaporated out into space when the Earth was still molten, or it sank into the core as the Earth cooled.

The clues to which path it took are provided by its four stable isotopes, variations of chromium that differ by the number of neutron particles inside the nucleus.

Chromium Disappearance

Using chromium isotope measurements from meteorites and the Earth’s crust, scientists put computers to work simulating the Earth’s early environment.

They were able to show for the first time that lighter chromium isotopes moved toward the core during the planet’s formation. Not only that, the simulations showed that the separation happened early in the planet’s building process, when smaller bodies were joining to form the Earth we know and love today.

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