 Ice cores drilled from glaciers and ice sheets are like a window into the past. Every year a new layer of frozen snow traps pollen, microbes, volcanic dust, among many other things. Even air bubbles act as a snapshot of the atmosphere that year. Scientists can use this data in combination with archeological and written records to understand rare but highly significant events in history, sometimes called black swan events. In the mid-1300s, for example, there was less lead in the atmosphere. Scientists think that's due to the sharp drop in mining and smelting during the black death plague in Europe and Asia. Ice cores in the Peruvian Andes and the Himalayas showed signs of an 18th century drought that spanned the globe. Today the world's ice is melting at an accelerating rate and some glaciers will soon completely disappear. Scientists like Lonnie Thompson and Ellen Mosley Thompson at The Ohio State University have been working to store ice cores from around the world to preserve the ice core record for future scientists.