Even if you’ve visited a mine, you still might not appreciate where metals come from. Humans have been digging metals out of the ground for thousands of years, but we’ve only been digging that metal out of the planet’s crust. This is weird, because when the Earth was forming billions of years ago, most of the precious metals like gold and platinum sank to the planet’s core with the iron that now dominates that space. That should have made those metals inaccessible to anyone on the surface, and yet we happily make use of these metals on a daily basis. It’s quite possible that the metal we find in the Earth’s crust actually came from space.
Assuming that our “native” gold, platinum, copper and more are all buried in the center of the planet, the shiny stuff we do dig up would have started on a meteorite. Billions of years ago, its hypothesized that a barrage of meteorites covered the Earth with a fresh supply of metals. Some of those metals were simply buried in the planet’s crust, while others may have been absorbed as deep as the mantle where they could have been churned and moved to new locations. Over time, some of these metals could have been pushed closer to the surface thanks to seismic activity, leaving us with situations like ancient Cyprus, where copper was found in such abundance we named the metal after the island.
Massive impacts on Mars
A twist on this model has also been proposed for other planets. Mars currently lacks the tectonic activity that could have moved and brought metals to its surface, and yet the Red Planet’s southern hemisphere seems to have plenty of metals that shouldn’t be there. That region also has a lot of scars from ancient impact craters, which helps support the idea that the metals on the surface of Mars were also delivered via meteorite billions of years ago.
In the proposed model, a huge meteor hit the planet, not only loading it with a new supply of metals, but also kicking up debris that would eventually coalesce into at least one of Mars’ two moons. It’s a tidy hypothesis, and it fits well with everything from concepts surrounding how planets are formed to why the surface of Mars’ northern hemisphere appears to be a different age than the southern hemisphere.