A short drive north of Fairbanks, Alaska, there's a red shed stuck right up against a hillside. The shed looks unremarkable, except for the door. It looks like a door to a walk-in freezer, with thick insulation and a heavy latch. Whatever is behind that door needs to stay very cold.
"Are you ready to go inside?" asks Dr. Thomas Douglas, a geochemist at the U.S. Army Corps of Engineers.