This 95 mile long coast was declared a natural World Heritage site in 2001. It exposes a unique record of 185 million years of Earth’s history from the Triassic (250 mya) through the Jurassic to the Cretaceous period (65 mya). Evidence of these distinct rock strata is for all to see as coastal erosion continues.
The oldest Triassic strata are seen between Exmouth and Lyme Regis - red cliffs containing pebbles and sand with few fossils. This was formed under desert conditions when Europe was close to the equator. During Jurassic times sea levels rose and fell intermittently and flooded the deserts with sand and clay with subsequent limestone and shale formation. This allowed marine reptiles and ammonites to flourish - the world famous fossils in the rocks between Lyme Regis and Swanage. Fossils of flying reptiles and some that lived on land have also been found here.
Because of erosion and tilting of the land towards the east the more recent Cretaceous rocks can be found in short stretches of the coast. Good sites are Beer, Lulworth, Swanage and Old Harry Rocks. This was a time of falling sea levels with subsequent formation of swamps, forests and lagoons. In these strata the large dinosaur fossils and their footprints have been found. Towards the end of this period, sea levels rose again with deposition of sandstones and chalk.
Still later, big earth movements caused the gigantic fold through Purbeck and then comparatively recent glaciations have completed the moulding of the landscape that we see today.