Discovered in the deep: the ancient plankton that fill a major evolutionary gap

Fossil plankton from half a billion years ago. These tiny algae measure much less than a millimetre in size. Photograph: THP Harvey

Half a billion years ago, the ocean was filling up with animals for the first time, including scuttling trilobites and spiky worms. Little is known, however, about what was happening further down the food chain.

Now, a British palaeontologist believes he may have found fossilised phytoplankton – forerunners of the tiny but vital algae that today suck masses of carbon out of the atmosphere and produce about half the oxygen we breathe. The fossils, dating back to the Cambrian period – 538m to 485m years ago – are microscopic, roughly the width of a human hair, and lived in the ocean back when there was no life on land.