 Ice cores provide valuable inventories of ancient climate. This slide here shows various levels of the ice core, illustrating how the physical properties of ice change from the surface down to the bottom. Ice formed from snow that was precipitated on the top of the glacier. The uppermost panel shows the properties of snow, very loosely compacted, showing a few annual layers that we'll describe later on in the snow, and very small trapped bubbles of air. In the middle panel, from deeper within the glacier, approximately 1,838 meters down, the ice is more compacted and shows a very strong annual banding with darker layers indicating slow accumulation rates of ice during the warmer months and lighter layers showing rapid accumulation of ice during the winter months. In this layer, you can see nicely trapped bubbles of gas. Close to the bottom of the glacier, where erosion of the underlying bedrock is common, the glacier has a dirty color, a brown color, because of the content of eroded minerals and rock particles in the ice. This here shows the glacier close to the base, about 3,000 meters below the surface.