A search for a missing metal in the Earth could help scientists understand the early stages of planet formation, U.S. researchers say.

Scientists studying the element chromium have known for years that the element's isotopes are relatively underrepresented in the Earth's mantle and crust, and the question has been whether they were volatile and disappeared into space in the planet's early period or got sucked in the Earth's deep core at some point.

University of California, Davis, geology professor Qing-Zhu Yin and others compared measurements of chromium isotopes in meteors with levels found in the Earth's crust.

The meteorites studied are from a class called chondrites, left over from the formation of the solar system more than 4.5 billion years ago, a UC Davis release said Thursday.

From the comparisons the researchers were able to determine that some forms of the element chromium separated and disappeared deep into the planet's core, and some 65 percent of the "missing" chromium is most likely in the Earth's core.

The separation must have happened early in the planet building process, the researchers say, probably in the multiple smaller bodies that assembled into the Earth or when the Earth was still molten but smaller than today.