Plankton helps form chalk

Plankton is a tiny organism found in the sea. A group of plankton named ‘coccolithophores’ comprises the chalk forming organisms. These organisms are microscopic and have shells made of lime. About 100 million years ago, during the Cretaceous period, these planktons settled down on the sea bed after death and formed lime mud. Subsequent layers of the skeletal remains of these organisms got added followed by the geological conditions of tremendous pressure and heat. This resulted in the formation of rocks which we now know as ‘chalk’.