New research offers a theory on how gold, platinum, and other precious metals found their way into Earth's mantle

Researchers from Yale and the Southwest Research Institute (SRI) believe they have discovered some extremely important new details on the history of gold.

The narrative starts with massive objects colliding violently in space, moves through a section of Earth's mantle that is partially burned, and concludes with valuable metals finding an unexpected resting place that is far closer to the planet's surface than scientists had anticipated.

In a paper published in the Proceedings of the National Academy of Sciences journal, Jun Korenaga, a professor of Earth and planetary sciences at Yale's Faculty of Arts and Sciences, and Simone Marchi, a researcher at SRI in Boulder, Colorado, give specifics.

Their new idea offers potential explanations for why valuable metals like gold, platinum, and others ended up in shallow pockets in Earth's mantle as opposed to the planet's core. In a broader sense, the new hypothesis provides information on planet formation across the cosmos.

"Our research is a good example of making an unexpected discovery after re-examining conventional wisdom," Korenaga stated.

Precious metals like gold and platinum were brought to Earth billions of years ago when the early proto-Earth collided with massive, moon-sized bodies in space, leaving behind deposits of materials that were folded into the current Earth. This has been proven by recent research conducted by scientists worldwide.

However, the mechanism of absorption has remained rather enigmatic.

In addition to their rarity, aesthetic appeal, and application in high-tech items, gold and platinum are regarded as extremely "siderophile" materials. Because of their strong attraction to the element iron, it is projected that they would gather nearly totally in the metallic core of Earth, either from direct impact merger or rapid ascent from the mantle into the core.

They shouldn't have gathered at or close to the Earth's surface according to this reasoning. Still, they did.

"Working with Simone, who is an expert on impact dynamics, I was able to come up with a novel solution to this conundrum," Korenaga stated.

The core of Korenaga and Marchi's idea is a narrow, "transient" zone in the mantle where the deeper portion of the mantle stays solid while the shallower portion melts. It was discovered by the researchers that this area had unique dynamic characteristics that allow it to effectively catch falling metallic particles and transfer them gradually to the remaining mantle.

According to their hypothesis, the transitory region's leftovers are still being delivered, and they will show up as "large low-shear-velocity provinces"—well-known geophysical anomalies in the deep mantle.

"This transient region almost always forms when a big impactor hits the early Earth, making our theory quite robust," Marchi stated.

According to the researchers, the new hypothesis reveals the vast range of time scales involved in Earth's creation and also provides an explanation for previously puzzling elements of the planet's geochemical and geophysical development.

"One of the remarkable things we found was that the dynamics of the transient mantle region take place in a very short amount of time—about a day—yet its influence on subsequent Earth evolution has lasted a few billion years," Korenaga stated.