Coloured scanning electron micrograph (SEM) of a fossilised Biddulphia sp. diatom surrounded by various cracked diatom and radiolaria parts. Diatoms contribute significantly to the oxygen in the atmosphere and are a fundamental link in the aquatic food chain. They are among the most diverse species on Earth, with the number of diatom species ranging from 10,000 to 200,000. Scientists are discovering new species every year. Magnification: x530 when printed 10 centimetres wide.