A. El Albani / IC2MP / CNRS - Université de Poitiers
An international team of researchers say they have uncovered the oldest evidence of movement in organisms in a 2.1-billion-year-old rock deposit.
According to a study published in the journal Proceedings of the National Academy of Sciences, tube-like structures discovered in the ancient rocks could be traces of early mobile multicellular organisms, potentially pushing back the date for the appearance of such creatures by 1.5 billion years.
The scientists from the University of Poitiers, France, found the structures in a shale rock deposit known as the Francevillian Formation located in Gabon—a country which lies on the Atlantic coast of Central Africa.
The same team has previously found what they say is evidence for the earliest known multicellular organisms in the deposit, according to another study published in 2014. However, these results have been contested by some researchers.
If the latest finding is indeed confirmed, it would indicate that both multicellular life and mobility in organisms appeared earlier than we thought. Currently, the oldest documented eukaryotes—a vast group of organisms which scientists consider that all multicellular life to belongs to—date back to 1.8 billion years ago. Meanwhile, the earliest evidence of movement in organisms is around 570 million years old.
For their study, the researchers used chemical analysis, 3D reconstructions and scanning electron microscope technology to examine the structures within the rock, which are still remarkably well preserved despite their age, according to a statement.
According to their data, the team concluded that the structures, some of which measure up to 170 millimeters in length, are biological in origin and represent strands of mucus left behind by organisms as they traveled through the mud in this primitive marine ecosystem around 2.1 billion years ago.
The team say that the size and complexity of the strands indicates they were made by multicellular eukaryotes, ruling out the possibility that they are geological in origin.
While it was difficult to know what these organisms looked like or how they behaved, the researchers suggest that they may have shared characteristics with amoeba colonies. These are made up of individual amoeba which can group together in clusters, essentially acting like a single organism. It’s possible that the driver behind the ancient organisms described in the study evolving to become mobile was a need to find food.
The suggestion that these findings represent the first evidence of locomotion in organisms raises a significant question: Why is there a gap of 1.5 billion years before we see similar signs of movement in life?
Some scientists have said we should be cautious about interpreting the new findings.
“I think the case for some biological connection is strong,” Graham Shields from University College London told the Guardian. “However, I don’t see much evidence for motility, i.e. willful movement through a sediment in search of food, other than superficial resemblance to trails or burrows.”