Researchers in Finland have created a timeline of volcanic ash deposits from Iceland and Alaska found in Finnish peatlands and lakes. They identified 19 different ash layers, with some being discovered in Finland for the first time. The oldest ash layer dates back to 7,000 years ago, while the most recent one is from 1875. This new timeline shows that tephra dating can be a useful method in Finland and helps refine our understanding of how volcanic ash has spread throughout history.