It sounds like something from a horror film, but scientists have found evidence of a slug-like organism slowly oozing through the mud two billion years ago – the earliest evidence of movement on Earth ever uncovered.
An international team of researchers made the finding in fossil deposits in Gabon, Central Africa. They discovered tiny tunnels in ancient rocks in the Francevillian inland sea – what was once a shallow, oxygenated marine environment.
Movement was an important stage in the evolution of life on Earth. Once animals could move, they could escape predators, look for food, and go off in search of mates. Until now, the first evidence for movement by complex, multicellular organisms dates back to around 600 million years ago. At 2.1 billion years old this latest discovery is much older.
The tubes are filled with pyrite crystals (generated by the transformation by bacteria of biological tissue) found in layers of clay minerals. Parallel horizontal layers are fossilized microbial mats © A. El Albani & A. Mazurier / IC2MP / CNRS – Université de Poitiers
The scientists found fossilised burrows in sedimentary rocks, which they then digitally reconstructed in 3D using a sophisticated X-ray imaging techniques. Chemical analysis then confirmed that the burrows were made by a biological entity. It’s thought that they were created by a cluster of cells which combined to form a slug-like, multicellular organism. The team also found fossilised microbial ‘carpets’ between the layers of rock, which may have acted as grazing grounds for the creature.
“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,” said Cardiff University’s Dr Ernest Chi Fru. “The results raise a number of fascinating questions about the history of life on Earth, and how and when organisms began to move.”
Around the time that these organisms were oozing through the mud, 2.1 billion years ago, atmospheric oxygen levels dropped below the level needed for the development of complex life on Earth. It wasn’t until around 600 million years ago that oxygen levels began to rise again, which is when complex animals began to thrive and move around, as revealed by fossil evidence from this period. However, this new finding suggests that movement actually evolved much earlier.
“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?” said Fru.
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