![0692 Fossil Air In A Glacial Cave Wall, Iceland By Barbara Bogacka](https://rps-assets.azureedge.net/media/t2vhgmbo/0692_fossil-air-in-a-glacial-cave-wall-iceland-by-barbara-bogacka.jpg?mode=max&width=1520&rnd=132653779538730000)
Glacier ice often contains bubbles of ancient air, captured at the time the water froze. These form a record of the atmosphere going back thousands of years. Scientists cut cores from the ice and sample the air in the bubbles to build up a picture of the past climate.