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.
Provided by
Yale University
