Evidence of the first signs of movement on Earth – probably made by a “slug-like” creature around 2.1 billion years ago – have been discovered in Africa.
The previous oldest remnants were dated to 570 million years ago, but the new evidence was uncovered in a fossil deposit in Gabon, where the oldest multi-cellular organisms have already been found.
An international team, coordinated by Professor Abderrazak El Albani, of the University of Poitiers in France, made the discovery in the black shales of the Paleoproterozoic Francevillian Group Fossil Formation in Gabon.
Located in the Franceville Basin, the deposit previously discovered by Prof El Albani’s team allowed scientists to re-date the appearance of multi-cellular life on Earth to 2.1 billion years – around 1.5 billion years earlier than previously thought.
At the time, researchers showed that the rich biodiversity co-occurred with a peak in dioxygenation of the atmosphere, and developed in a “calm and shallow” marine environment.
Now, in the same geological deposit, the team has uncovered the existence of fossilised traces of movement.
They say it shows that certain multi-cellular organisms in the primitive marine ecosystem were sophisticated enough to move through its mud, rich in organic matter.
Prof El Albani said: “The traces were analysed and reconstructed in 3D using X-ray computed micro-tomography, a non-destructive imaging technique.
“The more or less sinuous structures are tubular, of a generally consistent diameter of a few millimetres, and run through fine layers of sedimentary rock.
“Geometrical and chemical analysis reveals that they are biological in origin and appeared at the same time the sediment was deposited.”
He said the traces are located next to fossilised microbial biofilms, which formed carpets between the superficial sedimentary layers.
Prof El Albani added: “It is plausible that the organisms behind this phenomenon moved in search of nutritive elements and the dioxygen, both produced by cyanobacteria.
“What did these living elements look like? Though difficult to know for certain, they may have been similar to colonial amoebae, which cluster together when resources become scarce, forming a type of slug, which moves in search of a more favourable environment.”
Until now, the oldest traces of recognised movement were dated to 570 million years ago.
The research team said that the new discovery raises fresh questions regarding the history of life.
The findings were published in the journal Proceedings of the National Academy of Sciences (PNAS).
By Stephen Beech
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