SSS 2011-09-08

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Thar’s gold in them thar hills—and we may have meteorites¹ to thank. Because it appears that a rain of meteors nearly 4 billion years ago peppered the Earth’s exterior² with precious metals. So says a study in the journal Nature. 

 

When Earth was forming, molten iron sank to its center, creating the planet’s core. That iron carried with it a slew³ of iron-loving metals, including gold and platinum⁴. In fact, the Earth’s core is packed with enough precious metals to cover the entire planet four meters deep. 

 

But not all that glitters is down at the planet’s center. Today there’s enough gold in the Earth’s rocky shell to please prospectors—and to puzzle planetary scientists: why is that gold not down in the core, too? 

 

The answer, it seems, is that it wasn’t even on the Earth until after the core formed. Isotope⁵ concentrations in rock samples of different ages indicate that the composition of the Earth’s mantle⁶ changed after the planet was blasted with meteors 3.9 billion years ago. That bombardment coated our home with a thin veneer⁷ of riches. Which means that the gold in them thar hills is older than the hills.

 

Thanks for the minute. For Scientific American’s 60-Second Science. I’m Karen Hopkin.

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