Sedimentary rock layers are found in places all around the world. They can provide useful clues to the past. Sometimes a waterway cuts through the layers revealing a geologic record of the past. In other locations, scientists must dig trenches to see the layers. As the lower layers generally formed first, they are the oldest. Fossils within the rocks may allow some layers to be dated with accuracy. In other locations, clues may be sparse.
Searching for patterns in sedimentary rock layers is a bit like solving a puzzle. The picture emerges slowly, and the picture may tell a story. Landscapes are never static; they change over time. Continents move, landforms are raised and lowered, ocean shorelines advance and retreat. Biomes and their living organisms shift with the land
