Two billion-year old fossils reveal earliest evidence of living locomotion

These trace fossils are made up of a series of tiny tubes in the rock, measuring just a few millimeters wide. From this and analyses of the surrounding material, the researchers can infer a few things about the organism that left them. For one, it may have been fairly slug-like, and it seems to have lived in oxygenated waters, suggesting it depended on oxygen – a key development in the history of life on Earth.