Cyanotype by the Autrian professor of botany Julius Wiesner. Diatoms are a major group of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of the Earth's biomass: they generate about 20 to 50 percent of the oxygen produced on the planet each year and constitute nearly half of the organic material found in the oceans. (Image Source: The Metropolitan Museum)