The Isle of Wight is made up of many layers of sedimentary rock, originally deposited in rivers, on floodplains, in lakes and the sea over many millions of years.
The layers are formed of fine grained minerals, sands and fossils to form rocks like mudstones, shales, sandstones, siltstones and limestones. Some of the layers are poorly consolidated, and crumble easily into the sea, others are hard like the Chalk limestone which forms the high downland that runs across the Island from the Needles to Culver Cliff.
The oldest rocks on the Island can be found in Brook Bay on the south-west coast of the Island. They were deposited as part of an extensive river floodplain near the beginning of the Cretaceous Period. These are the rocks we call the Wealden.
The youngest rocks are peats and gravels that cap the cliffs on the southern half of the Island, near Newtown creek on the north coast and at Bembridge Forelands where peats and the famous Bembridge Raised Beach can be seen exposed in the cliffs. They formed from several hundred thousand years ago to the last few thousand years and help us understand the link between the Island and the rest of England during the Ice Ages.
The folowing information provides a brief summary of the evolution of the Island's geology over the four main geological Periods that left rock on the Island.
The Land of the Dinosaurs: 126 - 110 million years ago The Island’s oldest rocks are from units we call the Wealden. These multi-coloured mudstones and sandstones were laid down in rivers, in ponds and across extensive flooplains. This landscape was home to many types of dinosaur, including the plant eating Iguanodon and large carnivorous dinosaur Neovenator. Various types of plants and small creatures colonized the land on which the dinosaurs walked. In the air above flew pterosaurs hunting for fish in the rivers and ponds, and in the rivers swam crocodiles and turtles. 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 during this time. They are mainly sandstones and marine clays. The 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. Swimming above were large reptiles like ichthyosaurs and pliosaurs, and numerous smaller sharks. These were feeding on the various types of ammonites and fishes. The end of the Cretaceous is marked by the extinction of the dinosaurs and ammonites, along with many other plant and animal groups. The rocks from the end of the Cretaceous are missing from the Island; probably eroded away, we have no rocks left which record this interesting piece of earth history. A geological feature known as an unconformity separates the Cretaceous rocks from those of the Palaeogene above.
The Shallow Seas: 56 - 34 million years ago The layers of rock found that form most of the northern part of the Isle of Wight were laid down in warm shallow seas. The sea bed was home to over 500 different types of shellfish. Sharks and rays hunted in these waters. The rocks are mainly crumbly muds and sandstones. Amongst the more famous are the brightly coloured sands of Alum Bay. Just north of the central Chalk ridge these rocks have been turned upright by pressure from global plate movements; many of the layers are now vertical instead of horizontal.
The Everglades of Wight: 34 - 33 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. Sometimes we can find large trunks of blackened wood in the cliffs. After the Oligocene there are no more rocks to be found until those of the Quaternary. There is a gap of about 30 million years in our geology until then.
The Ice Ages: 2.588 million years ago to the present day The last few million years have seen many changes in climate, with numerous alternating warm and cold spells, each lasting tens of thousands of years, 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 remained trapped on the land as ice and snow, unable to return to the sea as it would have done in warmer times - global sea-level gradually 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 7,000 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. Fossils can be found from large elephants, bison and deer. We also find the tools of those other ancient animals that were living here - early humans.
For more detailed information you might like to look at our LGAP webpage and download the IW Local Geodiversity Action Plan. Part 2 of the LGAP provides a more detailed summary including reference to the structural changes that affected the landscape and entire shape of the Island.Our Earth's Timeline webpage includes information on the major time periods that geologists use to define the age of the Earth's many rocks and fossils. It also includes examples of important times in the development of life on our planet - major extinction events and the first appearance of new groups of organism. At the end is a brief summary of the time zones for the Isle of Wight, which shows were we fit in the overall timescale.Click on the images above to go to the appropriate webpage.The Rock CycleClick here for an animation of the process that creates, modifies and deposits the various rocks on the Earth's surface.
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