Earth History and the Jurassic Coast
What do you see, a stone or a tropical sea?
In the image shown here it may just look like a grey stone, but to a geologist it represents a tropical sea that disappeared millions of years ago. It is a window into a time when humans didn’t exist and when strange animals and plants flourished. When we read the clues we discover that every rock, pebble and grain of sand has its own story to tell.
The scientific investigation of rocks, and the fossils they contain, has revealed evidence charting the history of the Earth. Using information from sites around the world (and beyond) geologists have pieced together the grand tale of our planet’s past. The Jurassic Coast plays a vital role in this work because its rock record of the Mesozoic Era is exceptional.
This Time Spiral shows the history of our planet. There are details below about how the Jurassic Coast fits into that story and information about just a handful of the many other sites that help reveal Earth’s history.
The Quaternary period is known for Ice ages and human evolution. Key sites include La Brea Tar Pits in California USA, and Olduvai Gorge in Tanzania.
La Brea Tar Pits
The sticky tar that naturally seeps to the surface here has been trapping animals and plants for the last 40 thousand years and is one of the most famous sites in the world for ice age fossils. Specimens recovered include mammoths, sabre-toothed cats and giant dire wolves.
One of the key global sites revealing evidence of human evolution. Fossils of early humans discovered here date back two million years. The earliest traces of stone tools have also been found in this area.
Previously known as the Tertiary, these periods of Earth history chart the rise of mammals and the recovery of life following the end-Cretaceous mass extinction. A key site for Paleogene fossils is Messel Pit, in Germany.
Fossils that come from this old quarry are extraordinary. Some specimens even have their fur or feathers preserved. It is the best site known for understanding the animals and plants of the Eocene epoch, between 57 and 36 million years ago.
The Cretaceous Period, 145 – 66 million years ago
The Triassic, Jurassic and Cretaceous periods make up the Mesozoic Era, the age of giant reptiles and dinosaurs. Key sites include The Jurassic Coast and Dinosaur Provincial Park in Canada.
On the Jurassic Coast
The Cretaceous was a time of great change in our part of the world. Starting with low sea levels and coastal forests and swamps it ended with the great Chalk sea when sea levels were 200m higher than they are today. It is during this period that many of the most famous dinosaurs lived, like Tyrannosaurus Rex, although we don’t find their fossils on the Jurassic Coast.
Along the dramatic Purbeck coastline the rocks of the Cretaceous period are revealed – limestones from swamps and lagoons, sands and grits from rivers and shallow seas and the iconic white Chalk, the last rock to be laid down during the Mesezoic Era. Together they record 80 million years of history, the time between 145 and 65 million years ago.
Dinosaur Provincial Park
This famous area of badlands hides one of the richest sources dinosaur fossils in the world. Rocks laid down here between 74 and 77 million years ago have yielded fossilised sharks, rays and other fish, amphibians, lizards, turtles, crocodiles, mammals, various plants and over 40 species of dinosaur.
The Triassic, Jurassic and Cretaceous periods make up the Mesozoic Era, the age of giant reptiles and dinosaurs. The Jurassic is famous for its marine habitats and dinosaurs like Allosaurus and Stegosaurus. The Jurassic Coast is famous for fossils of Jurassic aged marine life.
On the Jurassic Coast
At the start of the Jurassic Period sea levels rose. The desert that had existed here during the Triassic Period was transformed into a tropical sea. The rich marine ecosystems supported a huge variety of animals from lobsters and starfish to sharks, Ichthyosaurs and even Pliosaurs, the mega-predators of the Jurassic oceans.
Grey clays, yellow sandstones and golden limestones form the cliffs in West Dorset. These rocks were laid down in shallow seas during the beginning and middle of the Jurassic Period, between 200 and 164 million years ago. They are a globally renowned source of fossils including ammonites, fish and giant marine reptiles.
The coast around Weymouth and Portland exposes rocks that formed towards the end of the Jurassic Period, between 164 and 145 million years ago. One of the very last rocks to form here in the Jurassic was the Portland Limestone, famous around the world as a highly desirable building stone.
The Triassic, Jurassic and Cretaceous periods make up the Mesozoic Era, the age of giant reptiles and dinosaurs. During The Triassic all the land masses of Earth were lumped together into one super-continent called Pangaea. The landscape was arid and most of Pangaea was covered by deserts. The Jurassic Coast is a key site for rare Triassic Fossils.
On the Jurassic Coast
The red rocks exposed in the cliffs of East Devon formed in deserts here between 252 and 201 million years ago, during the Triassic Period. Fossils from these rocks are rare but give us glimpses of how life evolved following the devastating mass extinction at the end of the Permian Period.
The Permian was a time of great deserts. It was during this period that the animals that would one day give rise to mammals and dinosaurs appeared. The Permian ended with the worst known mass extinction event, wiping out 96% of species. Sites include the Riviera Geopark and the Grand Canyon
To the West of the Jurassic Coast, in South Devon, lies another UNESCO site – the extraordinary Riviera Geopark. The geology there includes fantastic rocks from both the Permian Period and the Devonian Period (the clue is in the name… the Devonian period is named after Devon!)
An icon of the American landscape, and a World Heritage Site to boot, this deep gorge carves its way through layers of rock that reach back nearly two billion years. The record includes big gaps but is nonetheless an incredible source of information about Earth’s history. The youngest rocks exposed in the canyon are Permian in age.
The Carboniferous was a time when life flourished in vast forests and tropical seas. Giant amphibians dominated the land and an oxygen rich atmosphere allowed insects to become huge by today’s standards. A key site for the Carboniferous is Joggins Fossil Cliffs in Canada.
Joggins Fossil Cliffs
Nova Scotia, Canada
The rocks exposed here contain the world’s most complete fossil record of life from a time when lush forests covered much of the world’s tropics, 300 million years ago, during the Carboniferous period. The buried remains of these forests became the coal reserves that fueled the industrialisation of nations.
The Devonian period is known as the ‘age of fishes’ as it was during this time that they began to dominate life under water. Above water it was in the Devonian that the land was first colonised by animals as fish gave rise to primitive amphibians. Key sites include Miguasha National Park, a World Heritage Site in Canada.
Miguasha National Park
This site in Quebec is the best source of fossil Devonian fish anywhere in the world. Dating back 370 million years, these fossils help us understand the evolution of fish and their descendants – the air-breathing, four legged land animals. Oh, and the Devonian period?… its named after Devon, England, one of the first places that rocks of this age were studied
Miguasha National Park
The Devonian period is known as the ‘age of fishes’. This site in Quebec is the best source of fossil Devonian fish anywhere in the world. Dating back 370 million years, these fossils help us understand the evolution of fish and their descendants – air-breathing, four legged land animals. Oh, and the Devonian period?… its named after Devon, England, where rocks of this age were first studied.
During the Silurian Period the first fish with jaws appeared and fish also colonised fresh water for the first time. The earliest sure evidence of life on land comes from this time and includes fossilised moss-like plants and early spiders and centipedes.
Ordovician Period, 485 – 419 million years ago
In the Ordovician period most of the existing land masses were in the southern Hemisphere, meaning north of the tropics was almost entirely ocean. Although there is some evidence to suggest that plants had started to colonise the land in was in the marine habitats where life was truly abundant. Invertebrates like trilobites, snails and clams thrived while reefs were built by algae, sponges and early coral.
Cambrian Period, 540 – 485 million years ago
The Cambrian Period marks an important point in the history of life on Earth. During a time of rapid evolution and diversification, often known as the Cambrian ‘explosion’, life evolved into many of the major groups that still exist today. Innovations of evolution during the Cambrian Period include the first hard parts, like shells. Key sites include the legendary Burgess Shale in Canada.
British Columbia, Canada
One of the most incredible fossil sites known, the Burgess Shale dates to the very beginning of what might be called ‘complex life’, 540 million years ago during the Cambrian period. The creatures preserved in these rocks represent the ancestors of almost all known animal life, living and extinct.