The White Cliffs of Dover are made of trillions of tiny skeletons from prehistoric marine algae.

The White Cliffs of Dover are a geological marvel formed during the Late Cretaceous period, roughly 99 to 66 million years ago. At that time, much of Northwest Europe was submerged under a shallow, warm sea. The cliffs are composed primarily of chalk, a soft, white, porous form of limestone made of calcium carbonate. The primary building blocks of this chalk are coccoliths, which are individual plates from the skeletons of single-celled algae called coccolithophores. These organisms were so abundant that their remains accumulated on the ocean floor at a rate of only 0.5 to 2 centimeters every 1,000 years. Over millions of years, these deposits reached thicknesses of up to 500 meters in some areas. The sheer weight of the overlying water and subsequent sediment layers provided the pressure necessary to lithify these skeletons into rock. Tectonic movements associated with the Alpine orogeny eventually uplifted these seafloor deposits. This process, combined with the post-glacial rise in sea levels, exposed the vertical white faces we see today along the English Channel. Research from institutions like the British Geological Survey confirms that the cliffs continue to erode at an average rate of 1 centimeter per year. This constant erosion keeps the faces bright white by preventing the growth of vegetation. The cliffs remain one of the most significant carbon sinks on Earth, locking away prehistoric atmospheric carbon in mineral form.