How sensitive is Greenland’s ice to a warming world?

It sounds like something out of science fiction: In the late 1950s, the US Army carved a tiny “city” into the Greenland ice sheet, 800 miles from the North Pole. It had living facilities, and scientific labs, and working showers, all powered by one small nuclear reactor.

The research base was called “Camp Century,” a Cold War scientific project that helped researchers deepen their understanding of ice. As part of their efforts, they wound up drilling close to a mile down through the ice sheet to pull up an ice core: a series of long cylinders of ice that serve as a record of Earth’s history, with everything from atmospheric gases to volcanic fallout preserved in their tightly packed layers.

The ice from Camp Century has been thoroughly sampled and studied since it first came out of the ice sheet. It, along with the ice from many other ice cores, has taught us a lot about Earth’s climate going back tens of thousands of years — about how abruptly climate can change and the role that greenhouse gases play in warming.

But the drillers at Camp Century brought up more than just ice. They also brought up several feet of sediment from beneath it. Except, as a geoscientist named Paul Bierman, who wrote a whole book about the ice and sediment from Camp Century, explains, these samples went largely understudied for decades, with just a handful of papers written about them.

“ I think the focus of the community was almost laser on the ice and not on the stuff beneath it,” he says.

These sediments from underneath the ice were so undervalued, in fact, that they disappeared into some freezers in Denmark for years. Until, in 2017, some researchers found them again. And when scientists finally started to study these sediments in earnest, they discovered a bonanza of former lifeforms and a trove of information.

On the most recent episode of Vox’s Unexplainable podcast, we explore these long-ignored sediments, and learn what they can teach us about our climate past — and future.