Diatoms are single celled   algae with a shell made out of silica,  which are capable of living in fresh or marine water. These organisms are extremely important to life on earth. These microorganisms  are part of the phytoplankton ( from the Greek word phyton meaning plant), phytoplankton drifts in the ocean currents in the photic zone(top 30 m of the water column). Phytoplankton are extremely important because of their generation of large amounts of atmospheric oxygen and their energy contribution to the food chain.   Diatoms  are photoautotrophs, which means that they use solar energy to drive the synthesis of energy rich organic molecules from simple inorganic starting materials, such as carbon dioxide and water. Diatoms are very efficient photosynthesizers, about 55% of the energy they absorb from the sun is converted into energy of carbohydrate chemical bonds, which is one of the most efficient rates known. Excess oxygen not needed in cellular respiration is released through perforations in its shell into the water, where it is absorbed by other organisms, sediment or diffused into the atmosphere, this includes at least some of the oxygen we  breathe. Diatoms are important also because of their use in environmental studies, paleoenvironment, and their applications in the oil and gas industry.

 
Diatoms became important in phytoplanktonic production in the Cretaceous period; about 100 million years ago, when they started to increase the proportion of free oxygen in the atmosphere, and they have been the bigest contributors since.  Over 5000 species of diatoms are known, and they vary in shapes from round to elongated or triangular.

There are two main types of diatoms planktic and benthic. Plantik diatoms are suspended in the water column; in the photic zone, and drift with the ocean currents. Benthic diatoms normally have an elongate or pennate shape, and are found on the ocean floor in shallow environments.