Late in August, at a precisely specified point in the low Arctic, a geologist named Dave Freedman stood in a raw wind and a limitless expanse of tundra and began to thwack with a sledgehammer at a rock outcrop jutting up from the soil. Freedman, 29, works for a company called KoBold Metals, and the process that had brought him to this pair of GPS coordinates in Quebec’s far north was complex. But the rock had had its own journey. Before it was rock, it had been magma in the Earth’s mantle, part of a molten tongue tens of meters wide that had welled up as two tectonic plates spread apart 1.85 billion years ago. At first the magma had melted and eaten the layers of crust it flowed through, but, cooling as it rose, it eventually ran into resistance. The liquid pooled, like smoke along a ceiling, and then as the last of its heat bled out, solidified into a shelf of an igneous rock geologists call peridotite. Over the eons, it was lifted by tectonic collisions, tilted, folded, and broken. Glaciers ground it down. And then one day a helicopter descended from the sky and out jumped a slim, bearded man in Gore-Tex, with a high-visibility vest, a backpack, and a hammer.

After two ringing blows, a scone-size chunk of the outcrop broke off. Freedman hefted it up and blew on it. He grabbed the hand lens dangling from his vest and peered at the rock’s freshly exposed face, holding it a few inches from his own. The coarse grain was a good sign. So were the seaweed-green crystals of olivine. Evidently the magma had cooled slowly here, giving it time to react with neighboring rocks and to dyspeptically exsolve out the metals it had carried up from the mantle. “When you change the composition of a melt,” Freedman explained, “everything just goes haywire. Everything’s boiling, and things are unhappy, and it’s just a really chaotic environment.”