Chalk Cliffs

Photograph by Norbert Rosing

The chalk cliffs on Germany's Rügen Island rise 330 feet (100 meters) or more over the Baltic Sea. These ancient structures are made nearly entirely of the skeletons of calcite-covered plankton called coccolithophores, deposited by the trillions during the Cretaceous period. Sediments like these actually give the Cretaceous its name: Creta means "chalk" in Latin.