The weight of the glacier causes it to flow, pushing outward, like pancake batter, Cravens said. Ice at the edge may be distorted by this slow tumult, so scientists try to drill near the center, where deformation has been least severe, he said. For a core to be useful, annual deposition layers must be in their original order, not flipped or twisted. Each year is represented by two layers, winter and summer, visible as banding because of atmospheric dust trapped within, he said. Most research on ice cores revolves around the paleoclimate of earth, Cravens said.
Ice contains tiny pockets of gas, essentially captured fragments of atmosphere.
Scientists can tap into the pockets and determine gas ratios in the ancient air. Combined with other data, this can yield a model for ancient climate change, Cravens said. Past climate cannot be directly measured, however, in the way that organic material can be carbon-dated or the rings on a rattlesnake s tail counted to determine age. We have no marker for climate, Cravens said. We end up having to do everything by proxy.