In 2023, a team of researchers announced the discovery of the world’s oldest known protist fossils. These organisms, identified in Gabon’s Moulendé deposit, are thought to have evolved in the sea 2.1 billion years ago. Until now, the oldest similar forms were dated at 570 million years. Details of this work are published in the journal Earth Planetary Sciences Letters.
The Francevillien is a geological formation located in the Franceville region of southeastern Gabon. It is considered one of the most important sites for understanding the early evolution of life on Earth. A few years ago, a team led by Abderrazak El Albani of the Université de Poitiers/CNRS discovered the oldest fossils of multicellular organisms. These were dated at around 2.1 billion years, or 1.5 billion years older than previously thought.
As a reminder, multi-cellular organisms are made up of several distinct cells (each with a nucleus containing DNA) that work together to perform specific functions. These cells are organized into tissues, organs and systems, enabling these organisms to perform more complex tasks than the much simpler single-cell organisms (although some are capable of “changing their minds”). Their appearance was a key event in the evolution of life on Earth.
Over the years, researchers have identified several hundred specimens. These fossils (the “Gaboniontas”) probably lived in large colonies on the flat seabed.
New upheaval
More recently, the same team made another exciting discovery in the same region: protists (single-celled organisms). These organisms, dated to the same period, this time evolved in the water column, like today’s plankton. The largest specimens, which resembled flying saucers, measured up to 4.5 cm in diameter.
Some of the fossils discovered. Credits: A. El Albani & A. Mazurier
The researchers explain that they were able to establish their metabolism very precisely thanks to zinc, a bio-essential micronutrient essential for protein synthesis in eukaryotes.
In detail, this element comes in two isotopes, the lighter of which dominates inside cells. Using state-of-the-art instruments, the researchers were able to trace the distribution of these isotopes on a nanoscopic scale inside these specimens. They confirmed that the levels were half those found in the surrounding sediments. They were also able to determine that fossil size increased with zinc concentration.
These creatures floated in seawater 2.1 billion years ago. However, they also aggregated small and fine clay particles, which sometimes weighed them down to the point of sinking and settling on the seabed. This process could explain their presence in this Gabonese formation.
As with the multicellular eukaryotes mentioned at the beginning of the article, the oldest unicellular planktonic protists until now were those of the Ediacaran fauna, dated to 570 million years ago.
This discovery revolutionizes our understanding of the evolution of protists and eukaryotes, significantly pushing back the temporal boundaries of their existence on Earth. The work of Abderrazak El Albani’s team not only dates these organisms to 2.1 billion years ago but also provides valuable information about their lifestyle and environment. The ability to trace the metabolism of these fossils through zinc is a major technological advancement that opens up new perspectives for the study of early life. These results reinforce the importance of the Franceville site as a true treasure for paleontologists and highlight the potential for future discoveries in this region. By reevaluating the early stages of complex life on our planet, this research reminds us how much there is still to learn about the mysteries of our distant past.
Source: SciencePost
