Deep Time in a Drop The Strange Science of Ice Cores

Drop a piece of ancient glacier ice into a glass of water and listen. It pops and crackles, sometimes loudly enough to make you flinch. That sound is air escaping. Each bubble in the ice was sealed in as snow slowly compacted on a polar plateau. When the ice melts, the bubbles burst and release the atmosphere of a time before cities, before farms, and in the deepest cores, before our own species existed. You are hearing a breath of the ancient world.

That small fizz is the basis of one of the most powerful tools in climate science. The ice sheets of Antarctica and Greenland are enormous stacks of annual snowfall, laid down one year on top of another for hundreds of thousands of years. Scientists drill into them and pull up long cylinders of frozen time. From these they read the temperature of a long-vanished winter, the dust of a distant desert, the sulfur from a volcano that erupted before anyone wrote down its name, and the exact makeup of the air itself.

This is the story of how that reading became possible, what the ice has said, and why researchers are still camping on the coldest continent in search of ice that is older still.