The white color of the magnificent white cliffs of dover 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. About 20 million years ago, large glaciers cut through the rolling chalk hills. The land mass of Great Britain was separated from the rest of Europe when the Ice Age ended. It turned Great Britain into an island and left the cliffs exposed to wind, weather and tidal erosion.