National Geographic Daily News

Chalk Cliffs

Photograph by Norbert Rosing

The chalk cliffs on Germany's RĂ¼gen 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.

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