Finding ice this old is “fantastic,” says Eric Wolff, a paleoclimatologist at the University of Cambridge who wasn’t involved in the work. The climate clues in the oldest ice samples—those between 3 million and 6 million years old—might have been corrupted when the ice interacted with bedrock. But younger samples offer an unprecedented set of climate snapshots from an ancient world, Wolff adds. “Nothing’s quite as direct as actually taking a bubble, snapping it open, and putting it straight into a mass spectrometer.”