Life was creeping and crawling about the Earth 1.5 billion years earlier than previously thought, scientists have found, in a discovery which could rewrite evolution.
Previously it was thought that creatures began moving properly at around 570 million years ago shortly before the Cambrian explosion which sparked the first vertebrates.
Bacteria had previously flicked their tails, or flagella, to move around but no multi-cellular organisms had achieved locomotion.
But fossils dating from 2.1 billion years ago have shown that cells had already started to group together to form tiny slug-like organisms which slunk through the mud of ancient sea beds in search of food.
The tubular fossils were found in rocks in Gabon in west Africa by an international team including experts from Cardiff University.
Dr Ernest Chi Fru, from Cardiff's School of Earth and Ocean Sciences, said: "It is plausible that the organisms behind this phenomenon moved in search of nutrients and oxygen that were produced by bacteria mats on the seafloor-water interface.
"The results raise a number of fascinating questions about the history of life on Earth, and how and when organisms began to move.
"Was this a primitive biological innovation, a prelude to more perfected forms of locomotion seen around us today, or was this simply an experiment that was cut short?"
The earliest evidence for life on Earth comes from fossils of microscopic bacteria discovered in rock formations in Quebec, Canada which may date as early as 4.2 billion years ago. Bacterial life dominated until around the evolution of photosynthesis which led a build-up of oxygen, and new kinds of multicellular organisms form around 1.8 billion years ago.
But it was not until the Edicaran Period, at around 570 million years ago, that creatures with complex locomotion appeared, such as kimbella, a type of mollusc which shuffled along the seabed feeding on a gooey mat of microbes.
However the new findings show that basic lifeforms had learned to move far earlier with fossils discovered in the Franceville Basin, a calm and shallow ancient inland sea which existed 2.1 billion years ago in modern day Gabon.
Not only do the new fossils show earliest movement but the first evidence of multi-cellular organisms, 300 million years sooner than previously recorded. And they were large enough to have been visible to the naked eye.
The string-shaped fossils which range from 6mm to 170mm long, are preserved as tubular structures running through sedimentary rock in thin layers with a diameter of a few millimetres.
A detailed 3D analysis using a non-destructive X-ray imaging technique, alongside geometrical and chemical dating, revealed that the new fossils belong to an organism that likely spent most of its time in oxygenated waters, and was oxygen-dependent.
Next to these tubular structures researchers also found fossilies carpets of microorganisms, which would have provided the grazing grounds for the multicellular organisms.
Researchers believe the little worms may have operated in a similar way to how tiny groups of amoebae function today when resources become scarce, clustering together to form a type of slug which moves to find a more favourable environment.
The research was published in the journal Proceedings of the National Academy of Sciences.