Whilst it might be easy to dismiss stromatolites and thrombolites as ‘boring’ because they resemble giant grey rocks, such strange formations are among the oldest living organisms on the planet and have a remarkable story to tell. These living fossils have survived for over 3.5 billion years and can still be found in a few special places today. The best examples of stromatolites and thrombolites on the Jurassic Coast are around 145 million years old and can be seen at the Fossil Forest near Lulworth Cove.
As we approached the beginning of the Cretaceous Period, falling sea levels exposed large areas of land for the first time in millions of years. A shallow saltwater lagoon was left behind, cut off from the retreating sea. In the years that followed, the margins of this lagoon were colonised by plants.
Sadly, this Fossil Forest was a brief oasis in a hostile environment. As water levels in the lagoon began to rise, the forest was flooded with salt-rich water. Very few living creatures were able to survive in these extreme conditions. As the trees died, their fallen trunks and decaying stumps were smothered by gooey mats of algae. The algae trapped sediment and mud which eventually hardened to form stromatolites and thrombolites. Within these stony structures, the remains of trees sometimes remain.
Stromatolites and thrombolites come in all shapes and sizes. Long, straight forms once covered fallen trees and circular forms grew around the base of upright tree trunks.
You too can discover this unique part of the Jurassic Coast’s story. The long-lost landscape of the Fossil Forest is preserved on a rocky ledge to the east of Lulworth Cove. This feature is sensitive to damage so please do not attempt to collect the fossils.