White Cliffs of Dover
One of England’s most famous natural landmarks, the White Cliffs of Dover run along the northwestern side of the Strait of Dover, the narrowest part of the English Channel. They are complemented on the French side of the Strait by similar cliffs at Cap Blanc Nez. The chalk from which the cliffs are composed was formed between 100 million and 70 million years ago, when a large part of what is now northwestern Europe was underwater. The shells of tiny planktonic organisms that inhabited those seas gradually accumulated on the sea floor and became compressed into a layer of chalk that was several hundred yards thick. Subsequently, as the sea level fell during successive ice ages, this mass of chalk lay above the sea, and it later formed a land bridge between present-day England and France. However, about 8,500 years ago, the buildup of a large lake in an area now occupied by the southern North Sea caused a breach in the land-bridge. It eroded rapidly, causing flooding of the area that now forms the English Channel.
Today, the cliffs at Dover continue to be eroded at an average rate of an inch or two per year. Occasionally a large chunk detaches from the cliff edge and falls to the ground. Many marine fossils have been discovered in the cliffs, ranging from sharks’ teeth to sponges and corals.