Planktonic foraminifera are single celled organisms that are highly abundant in modern oceans and a hugely important part of the Earth’s carbon cycle. Each cell builds a hard calcite ‘test’ around itself in a huge variety of shapes. These tests continuously rain down on to the ocean floor leaving continuous records of how these organisms have changed over millions of years. They form the most complete fossil record we have, and are a very useful tool in everything from the oil industry to understanding how evolution works.