Reading past environments

The natural processes that shape the Earth today worked the same way in the past, so what we see happening now explains what the rocks record: 'the present is the key to the past'. Geologists use it to rebuild where seas, forests, deserts and ice once were. Corals today live only in warm, clear, shallow seas, so fossil corals in a mountain mean a warm, shallow sea was there. Coal forms from plants buried in swampy forests, so a coal seam means a warm, wet forest. Rock salt and gypsum are left when salty water evaporates, so they mean a hot, dry climate with shallow lakes or seas drying up, like the salt and gypsum of Semnan province. Scratched, polished rock and jumbled boulders mean glaciers. Fossils of sea creatures in general tell how deep the water was.