Signs of life
541 million years ago, some of the earliest mobile organisms left these tracks in the mud.
This image shows scans of microscopic trace fossils more than 500 million years old. They show the tracks and burrows of what scientists believe were some of the first organisms capable of active movement.
Discovered in sediment in western Brazil, the burrows are between 50 and 600 microns in diameter. The creatures that made them – most likely something like modern nematodes or roundworms, which had no skeletons to leave behind – would have been around the size of a human hair.
These fossils have been dated to the transition between the Ediacaran and Cambrian periods of Earth’s history around 541 million years ago.