The white color comes from the chalk from which the cliffs are made. More than 100 million years ago, the area that is now the south of England was covered by a warm sea. Microscopic plankton lived in the upper levels of this sea, and when they died their bodies sank to the seabed. Over time it built into a thick layer, and the weight of water pressing down on the seabed turned the shell-rich mud into the soft rock known as chalk.
Large glaciers cut through the rolling chalk hills about 20 million years ago. The land mass of Great Britain was separated from the rest of Europe when the Ice Age ended around 10,000 years ago, it turned Great Britain into an island and left the cliffs exposed to wind, weather and tidal erosion.
The cliffs' past as a marine environment has made it a rich source of marine fossils. Paleontologists have found the fossils of numerous sea creatures, including a variety of shellfish and sharks. The cliffs are a protected Site of Special Scientific Interest, which means it is not permitted to collect fossils from the cliffs themselves. Fossil hunters can examine the rocks that have fallen from the cliffs.
The National Trust estimates between 2 and 5 cm of the cliffs are lost to erosion each year. The Trust believes this rate of erosion is only likely to increase if sea levels rise. Another problem are periodic cliff falls that can destroy a meter of rock in a single incident.
The cliffs have been an important icon for the British people, perhaps most notably during World War II when the song "The White Cliffs of Dover" became immensely popular. The song, sung by Vera Lynn, looked forward to a time when the war would be over and people could resume their peacetime lives. Asked by the London "Independent" in 1999 whether she ever got tired of singing it, Vera Lynn answered, "No ... It meant so much to everyone. The white cliffs of Dover were the last thing the boys saw as they were leaving (for war). The song meant home to them."
