Diatoms, an estimated 6 million of which may be found in a single cubic foot of salt water, are both prolific and important. Most diatoms are free-floating and serve as a food source form many other animals. Diatomaceous earth, a material consisting of fossilized diatoms, is often a component of various products, such as filters, insulation, abrasives, paints, and varnishes. Moreover, the extensive fossil record of diatoms has made them extremely useful to scientists researching changes in ecological conditions over long periods of time.