Sunday , June 20 2021

2-billion-year-old scavengers could be the earliest evidence of a mobile lifestyle

Tubular structures embedded in the rock.
Photo: A. El Albani and A. Mazurier / IC2MP CNRS – University of Poitiers

The open discovery of fossil traces of 2.1 billion years, dug into sedimentary rocks, repels the earliest evidence of a self-propelled movement of an organism on Earth with a massive 1.5 billion years.

A new study, published Monday in a collection of reports from the National Academy of Sciences, shows that ancient life on earth has acquired the capacity for self-propelled movement for at least 2.1 billion years and not 570 million years ago, as previous research suggests . The evidence of this apparent movement, also known as mobility, is presented in the form of small petrified winding signs embedded in the ancient sedimentary rocks.

The X-ray image reveals tube-like structures embedded in the sedimentary rock.
Photo: A. El Albani and A. Mazurier / IC2MP CNRS – University of Poitiers

In 2010, the lead author of the new study, Abderrazak El Albani of CNRS-Université de Poitiers, discovered the earliest evidence of complex multi-cell life in the Francevillian basin in the Haut-Ogooué province in Gabon, Central Africa. Dated at 2.1 billion years, the fossils were 1.5 billion years older than the previous 600 million years ago. This ancient life, the authors suggest, lives in shallow marine environments with sufficient access to oxygen.

The new fossils found in the French basin suggest that some forms of this ancient life have developed the ability to move through rich mud on this shallow seabed. According to the new study, petrified cloud traces found in these rocks are the tunnels left by these primitive creatures as they roll in search of nutrients. If confirmed, this would be the earliest evidence of mobility in eukaryotic life, ie. animal forms with complex cells and a clearly defined nucleus.

– In the galleries [of the x-ray images] – said El Albani in a statement. "But credit really has to go in the quality of these rocks, which are able to exclusively keep the movement of primitive organisms."

For the study, El Albani and his colleagues used chemical analysis, scanning electron microscopy and X-ray computer micrographs, the latter of which allows the crystal clear 3D perspective of rock embedded curls. String strings, of which 80 were found, were about 6 millimeters wide and stretched to a maximum length of 170 millimeters. Some of these obvious tunnels intertwine, stretching vertically and horizontally.

Chemical analysis shows that the characteristics are the result of biological, not geological processes, and occur at the same time as the sludge is formed. Organic matter in the rock "can be either a body that decomposes there or a mucus left by the body like a snail's path," El Albani explains in the statement.

These features are located near fossilized microbial mats (layered sheets of fossilized microorganisms). The authors suggest that apparently mobile eukaryotes move around in the dirt in search of nutrients produced by the cyanobacteria responsible for microbial mats. It is important that at that time the Earth is already rich in oxygen, which makes the emergence of a complex life an obvious opportunity.

Stunningly, the tunnels were not formed by one man, but rather by mass gathering, according to the new study. These primitive eukaryotes, called Gabonita by the authors, gathered together massively, shaping the shape of a rat. This allows them to move through the mud – both in vertical and in the horizontal directions – in search of food and areas rich in oxygen, similar to how modern colonial amaebies do. Technically speaking, these creatures were mobile, but they achieved their mobility through collective group action, according to the new study.

The authors do not know whether this is a one-time thing – a kind of unsuccessful experiment – or an important evolutionary precursor to the moving life. After this period of Earth's history, a great period of ice on Earth caused a sharp drop in oxygen levels, making the life of the alleged Gabonita extremely difficult, if not impossible. They could be destroyed, and the agility to return to another species many millions of years later. Either managed to survive, setting the foundations of a critical evolutionary adaptation.

Or they do not exist at all. Speaking to The Guardian, Graham Shields of the University College London said the tunnels look organic by nature, but the evidence provided does not make it clear that mobile life is included. Structures, he said, may be remnants of microbial mats or pipe-like creatures known as Grypania. Shields said he did not "see much evidence of mobility … except the superficial resemblance to paths or holes."

The claim that self-sufficient eukaryotes exist 2.1 billion years ago is quite unusual, no doubt. Hence, other researchers should look at the samples themselves to confirm the findings while continuing to search for more fossils. If confirmed, however, this discovery means that complex life has arisen relatively early in Earth's history and does not waste time on developing means of self-propulsion. The primitive life seemed to be eager to leave.

[Proceedings of the National Academy of Sciences]

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