History of the Jurassic Coast Part 1. Written by Roy Beal
From the red cliffs at Exmouth, to the chalk cliffs near Studland, the Jurassic Coast is a 95 mile wonder of the natural world. It's unique too. This coastline is the only place on the planet where there is evidence from all three periods of the Mesozoic Era all in one place - the Triassic, Jurassic and Cretaceous periods of Earth's past give us a history lesson that stretches over more than 250 million years.
View from Jacobs Ladder, Sidmouth
Let's start with the vividly coloured sandstone cliffs, predominantly found between Exmouth and Lyme Regis. These come from the earliest of the three periods, the Triassic, which had a hot and dry climate with vast deserts.
It's unusual to find any fossils along this stretch of coast, but they do turn up on occasion. If you are fortunate to stumble upon a fossil, it's likely to be between 201 and 252 million years old! This period was when the first true mammals appeared and started evolving.
The colouration of the soil can extend its thanks to the iron content it had. The iron oxidised (rusted) due to the climate, giving it the reddish colour we see today. The sandstone is soft and coastal erosion over the millennia has created some fabulous features, such as the stacks visible at Ladram Bay.
Science has shown the oxygen content of the air was 80% of what we have today. The Triassic Period was the shortest of the Mesozoic Era, spanning just 50 million years but, during in this time, a supercontinent known as Pangaea was gradually moving apart. By the late Triassic and early Jurassic, there were two separate landmasses, Laurasia to the north and Gondwana to the south.
Various climate and environment changes are believed to have caused a mass extinction event which led to the Jurassic period, which was under the rule of the dinosaurs. Whether it was volcanic eruptions, sea-level fluctuations or even seawater acidity changes, a massive event occurred, completely changing the landscape and environment.
The Jurassic period was a warm and humid time and the creation of rainforests replaced the previous deserts. The first birds appeared and the oxygen content was 130% of what we know today! Sea levels rose and tropical seas were the order of the day along our Jurassic Coast. Dinosaurs and marine reptiles were predominant and it is thought that the first flowering plants developed towards the end of the period.
Axe Undercliffs fossil next to Roy's size 11!
The rock strata is a blue-grey colour and it's this period that provides us with the most exciting fossils along the Jurassic Coast. Charmouth and Chapmans Pool have beautiful fossils, easily found with a gentle stroll at low tide. The Undercliffs between Seaton and Lyme Regis also show a wonderful selection of fossils as well as a fascinating view of some spectacular geology from this time.
Sealife was in abundance during this period, the climate perfect for the evolution of predators such as the Ichthyosaur and the Ammenites that we know and love as the symbol for this World Heritage Site. We also have this period to thank for the advent of petroleum-based production, aka Fossil Fuels.
Land masses continued to move and create rifts, the Atlantic Ocean started to form and after about 56 million years, we entered the Cretaceous period, the longest of the three Mesozoic periods. The 79 million year Cretaceous times provided us with the chalk cliffs we see around Beer, Seaton and at the other end of the Jurassic Coast at Old Harry Rocks. There is no obvious event that marks the change into this period, although there is evidence of a mass extinction event at the end of the period.
With 150% of the oxygen we have today, the climate was quite warm and the sea levels very high, creating many inland seas. The late Jurassic and early Cretaceous had a period of cooling with evidence of glaciers in higher latitudes but as the period continued, temperatures rose again and it is believed that it was a period of volcanic eruptions and very high carbon dioxide levels.
Bees appeared during Cretaceous times, along with other insects like ants. Plant and tree life started to spread with early figs and magnolias appearing. The chalk cliffs we see today are formed from a type of algae that was rife in the Cretaceous seas called Coccoliths.
This period ended with mass extinction events, possibly from asteroid impacts and volcanic activity which blocked the sun and reduced photosynthesis. There is another school of thought that believes it was a gradual shift in climate and sea levels, perhaps similar to what we are experiencing now?
The view toward Bat Head, near Durdle Door
Throughout these three periods, the land moved, rose, dropped and thus created the coastline we see today. There is a great 'fault' at Seaton Hole where one can see a transition between the Triassic and Cretaceous. The Jurassic period appears to be missing here, although just a mile or so to the east, it pops back up again.
Our planet is forever changing. From its formation 4500 million years ago, it has evolved and altered and humans have only been here for a very short time. The earliest human (Homo Sapien - more on this subject in part 2) remains have only been dated to 200,000 years old. Isn't it mind-boggling to think that the Jurassic Coast is up to 252 million years old?
When you consider how much we have achieved, and destroyed, in the relatively short time we've existed, it's still obvious that we are just the merest speck of dust on the planetary clock.
Looking out to sea through Stair Hole, near Lulworth Cove
Humbling isn't it?
If you like to know more about the Jurassic Coast, I can highly recommend joining the Jurassic Coast Trust. They offer all manner of fantastic things to their members. Click here to find out more.