Diatoms are single-celled algae which make up a large part of the ocean plankton. This means that they are an important part of the oceanic food chain. The unique structure of diatoms is a hard, glass shell that remains even after the death of the organism. Many scientists theorize that millions of years ago, after diatoms died and settled to the ocean floor, they were buried by sediments. Over time, the heat and pressure of the sediment layers most likely resulted in the formation of —