How the Earth Got its Gold

We publish courtesy of Israeli Diamond Industry Blog

Author: Roe Kalb

A new study from the Southwest Research Institute in Boulder, Colorado suggests that the Earth’s precious metal resources might be the result of huge asteroids hitting the planet.
It has been long established that the Earth’s mantle (the liquid layer below the crust) contained a large amount of “iron-loving” or siderophile elements, which include gold.



Thus far, theories have suggested that these elements, which tend to affiliate with iron when liquid, entered the mantle after the planet’s core was formed through an impact, but the nature of what impacted the nascent planet was unknown.

The Southwest team, led by William Bottke, employed computer simulations that showed that a series of random impacts that took place some 4.5 billion years ago are what gave the Earth its gold and other siderophile elements.

The new research indicates that what hit the young planet were rocky objects that remained after the solar system’s planets were formed, the largest of which was close to the size of Pluto (3,220 kilometers in diameter.)

Nor was Earth the only body to sustain these cosmic whacks. Bottke’s team concluded that the same rocky objects hit the moon and Mars during the same period, leaving siderophile elements in both places. In addition, the moon’s water might be the result of these impacts.

According to Bottke, the presence of gold and other iron-loving elements shows us what was impacting the Earth, moon, and Mars in what he called the “last-gasp growth spurt they had.”

Bottke’s team assessed that the Earth’s gold and other siderophile elements were delivered in a limited number of massive impacts on the planet that missed the moon, but only by chance. The moon, about 1/20th the size of the Earth, should theoretically contain about 1/20th of its precious minerals – but it only contains a thousandth of the amount of minerals the Earth does.

This discrepancy, the team explains, can only be explained as the result of a limited number of major impacts rather than a continual bombardment, with a lucky “roll of the dice” sending one massive object toward the Earth rather than the moon, leaving behind the precious minerals we mine and use today.

The Southwest Research Institute’s findings were conducted using the Monte Carlo mathematical tool and published in Science.


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