In 1961—the year before he became the anchorman for CBS News—Walter Cronkite visited Camp Century, an unusual military compound on the Greenland ice sheet. Carved under the snow and ice, Camp Century had a main street and prefab housing for 250 soldiers and scientists—all powered by a pint-sized nuclear reactor. To get there, Cronkite endured a multiday haul from the edge of the ice sheet by “wanigan”—a heated, insulated trailer hitched to a massive Caterpillar tractor traveling at the speed of a slow-walking human.

Cronkite’s televised report was wide-eyed at the base’s scale and audacity—there were mess halls, a church, and even the hair-cutting services of a barber named Jordon. When Cronkite asked Camp Century’s commanding officer, Tom Evans, about his objectives, Evans rattled off three: “The first one is to test out the number of promising new concepts of polar construction. And the second one is to provide a really practical field test of this new nuclear plant. And, finally, we’re building Camp Century to provide a good base, here, in the interior of Greenland, where the scientists can carry on their R&D activities.”

Excerpted from The Ice at the End of the World: An Epic Journey into Greenland's Buried Past and Our Perilous Future, by Jon Gertner. Buy on Amazon. Random House

When Evans talked to Cronkite, some researchers and soldiers working at Century were aware that his answer was not entirely forthright. There was another project at the encampment that Evans did not discuss. In trenches under the ice about a quarter mile from the main camp, an Army Corps engineer was secretly moving massive hunks of pig iron on a flatbed rail car—thousands of pounds of raw metal meant to approximate the weight of an intermediate range ballistic missile.

Many decades later, long after Camp Century had been abandoned, it would come to light that the US military was proposing something called the Iceworm system: a nuclear arsenal of 600 ballistic missiles, trained toward the Soviet Union, which would be in constant motion by rail under the Greenland ice sheet. Iceworm was never built. The military soon understood that Camp Century was doomed. At best it would last 10 years, they acknowledged, at which point the overburden of snow would push down on the roof, compress the walls, and thus destroy it.

Camp Century was a perfect example of Cold War paranoia and eccentricity: an improbable outpost that was expensive to build, difficult to maintain, and unpleasant to live within. The irony was that Camp Century was also the site of an inspired and historic engineering experiment. It just happened to be an experiment that the US Army didn’t care that much about. In fact, the importance of the research project being conducted at Camp Century wouldn’t be truly understood for decades.

It was there, in a cavern located dozens of feet below the surface of snow and ice, that scientists were perfecting a new method that would allow them to read Earth’s history. A small number of glaciologists had already come to understand that the ice sheet probably contained a frozen archive of long-ago events and temperatures—that it was encrypted, in some yet-to-be-deciphered way, with a code to the past.

This code was locked within the ice amid the snow crystals that had fallen thousands of years before. The working assumption was that by drilling into the ice you could pull up a sample—a cylinder of ice that became known as a core—and use laboratory tools to unlock mysteries from the past. The deeper you drilled down, the farther you went back in time.

“The army allowed us to freeload with them,” recalls Chet Langway, the geologist who was in charge of cataloging and analyzing the ice cores at Camp Century. And since the army was maintaining the appearance that the camp was for scientific research rather than for nuclear missile research, officials at Camp Century welcomed the prospect of showing visitors what the drillers were up to. Cronkite visited the early stages of the drilling project. “We were sort of a cover, if you will,” Langway says, even though his team’s goal—to reach bedrock—was deeply serious.