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Top Comments: The Earth's Mantle Dynamics Kept Precious Metals Close to Crust [1]

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Date: 2023-10-22  

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For many centuries, humans have been mining dense precious metals from the Earth’s crust: gold, platinum, and palladium, among others. In addition to their use in jewelry, they have have use in consumer goods, such as catalytic converters, and electronics. Among geophysicists though, it’s a puzzle understanding why's such metals are found in Earth’s crust. It would seem that, in Earth’s early history, their high densities would have driven all of these elements to the Earth’s core where they would be unavailable to miners.

Why didn't this happen? What prevented the precious metals present on the early Earth from sinking to the core?

It’s generally agreed that asteroids and other rocky bodies brought precious metals to the young Earth through collision, at a time in the history of the Solar System when such collisions were quite common. Simulations run on computer by researchers at the Southwest Research Institute in Colorado, and at Yale University, revealed a possible mechanism that would prevent these delivered precious metals from sinking to the core. If the colliding body delivering the metals were large enough, its collision would obliterate the colliding body while creating a sea of magma on the Earth’s surface. The metals would sink through the liquefied crust, but would be deterred from sinking further when it got to the mantle below the crust. Under such a collision, while the crust could melt completely, the mantle would still be semi-solid, allowing the precious metals to percolate some distance within it, but not sink any further. Then, in the billions of years that followed, the geologic activity roiling the mantle could cause the precious metals to rise to the crust where, much later, humans could find them.

It turns out there there is evidence of regions in the mantle where such impacts occurred. These are regions where the speed of earthquake-induced waves travel at an anomalously slow rate. Until now, there has been no explanation for how these regions came about, but they could be the pieces of mantle that got hit by these large rocky bodies carrying precious metals.

While this mechanism seems plausible, it requires confirmation, but at least there’s now a way to explain how we have access to so many metals in large quantities.

Comments are below the fold.

Top Comments (October 21-22, 2023):

From thesphynx:

LimeyExpatDave's thoughts on the reporting of tragedies and the celebration of ordinary people who do extraordinary things. From mettle fatigue’s recommended post about how a Bedouin bus driver saved 30 festival-goers from the Hamas massacre.

From fromberkeleytocville:

This comment by Caliron, regarding cats and the Speakership, from Jen Hayden’s front page post Sunday funday news.

Top Mojo (October 20, 2023):

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