We use a variety of systems for extracting cores from bogs and lakes. Here’s a video we made a few years ago of how we use a Russian Corer to extract a 50cm long core from a peat bog. This bog is around six meters deep, so we extract a sequence of cores that, together, form an uninterrupted sample of the entire depth of the bog.
Peat bogs accumulate over time, as living things die but do not decompose in the wet conditions. This means the material at the bottom is the oldest, and the material at the top is the youngest. Radiocarbon dating and other methods allow us to establish exactly how old, and microscopic analysis of the material allows us to reconstruct changes in conditions of the bog through time.