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Geological History

The Isle of Wight is made up of layers of sedimentary rock. These rocks are formed from sand and mud laid down by rivers and in the sea, between 126 and 32 million years ago. We know how old these rocks are from the fossils we find within them, and by comparison with other rocks of known age.

Geologists give names to rocks, which describe what they are made of; for example sandstone, mudstone and limestone. These rocks are given other names which are specific to individual layers. Some of these names are used in the geological history of the Island given below.

THE CRETACEOUS

The Land of the Dinosaurs: 126 - 110 million years ago
The Island’s oldest rocks are called the Wealden. These mudstones and sandstones were laid down in rivers and ponds. This landscape was home to dinosaurs such as the plant eating Iguanodon. The Island has become famous for its many dinosaur bones and footprints.

The Tropical Seas: 109 - 100 million years ago
About 109 million years ago the sea flooded over the land of the dinosaurs. The rocks geologists call the Lower and Upper Greensands were laid down, these are sandstones. These rocks contain the fossilized remains of corals, ammonites, clams and lobsters which lived in that ancient tropical sea.

The Chalk Sea: 100 - 65 million years ago
The limestone we call the Chalk is made from billions of tiny shells of plankton which lived in the clear warm waters. The sea floor was home to sea urchins, sponges and huge oysters. The end of the Cretaceous is marked by the extinction of the dinosaurs and ammonites, along with many other plant and animal groups. There are no rocks on the Island which record this interesting piece of earth history. A geological feature known as a unconformity separates the Cretaceous rocks from those of the Palaeogene.

THE EOCENE

The Shallow Seas: 65 - 40 million years ago
The layers of rock found under the northern part of the Isle of Wight were laid down in a warm shallow sea. The sea bed was home to over 500 different types of shellfish. Sharks and rays hunted in these waters.

THE OLIGOCENE

The Everglades of Wight: 40 - 32 million years ago
During the Oligocene shallow lagoons and swamps formed, which resembled the modern day Florida Everglades. The swamps were home to alligators, turtles and pig-like mammals. The thick muds which formed here contain many layers of shells. By about 32 million years ago the lagoons had silted up. No rocks from this period remain which record events after that date.

THE QUATERNARY

The Ice Ages: 2 million years ago to the present day
The last two million years have seen many changes in climate, with many alternating warm and cold climates, caused by wobbles in the Earth's orbit and its axis. The time known as the Quaternary is recorded on the Island by extensive patches of gravel, clay and peat. When the climate was colder water from the sea transferred to snow and ice on the land surface and the sea-level fell. When it became warmer the ice melted and sea-level rose. The last ice age ended about 10,000 years ago. Between then and now sea-levels have risen again. The Isle of Wight was probably separated from the mainland about 6,000 years ago when the rising sea flooded into the Solent and cut the Chalk ridge between the Needles and Purbeck; cutting the Island off from the mainland.

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Dinosaur Isle,
Culver Parade,
Sandown,
Isle of Wight
PO36 8QA

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