Image caption
This chunk of ice comes from the first ice core drilled at Mt. Hunter, Alaska. Embedded pebbles and dust tell researchers that this portion of the ice core is from the bottom of a glacier, right above bedrock. Paleoclimatologists analyze isotopes of water in the annual layers of ice to determine the regional temperature when it fell as snow. Scientists also check the composition of air in trapped air bubbles to understand how the atmosphere changed over time. Photo by Mike Waszkiewicz.