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Oxygen dynamics and early steps towards multicellularity 2.1 billion years ago

2019-12-03 122

TitleOxygen dynamics and early steps towards multicellularity 2.1 billion years ago



SpeakerAbder El Albani, Professor, Université de Poitiers


     Dr. Abder El Albani is a professor of Université de Poitiers at the Hydrasa laboratory (IC2MP - CNRS), France . His research focuses on sedimentology, geobiology and paleo-environment. He is known for having discovered the oldest known fossils of multicellular organisms in the 2.1 billion year-old black shales of the Paleoproterozoic Francevillian Group Fossil Formation in Gabon. The discovery of these organisms moved back the date of the emergence of a multicellular life of 1.5 billion year. This discovery has also increased our current knowledge of the evolution of the biosphere on Earth. He has published multiple papers in high impact journals like Nature and PNAS.


     Animals appeared a little more than half a billion years ago, changing the Earth’s biosphere forever. Predation, burrowing, and all other modes of life available to animals pushed evolution in numerous directions. This was the “Cambrian explosion”. Animals were not the first, nor the only, multicellular macro-organisms, however. Scattered fossil occurrences show that large individuals using cells as building blocks appeared a number of times during the latter part of the Proterozoic Eon (2.5 to 0.54 billion years ago). Some of these early lineages (such as red or green algae) still exist.

    Reported in Nature Magazine in 2010, in Plos One in June 2014 and PNAS 2019 is the recent discovery of centimeter-sized fossils from black shales in Gabon represented by more than 500 specimens. These macro-fossils reveal that macro-organisms growing in a coordinated manner (a prerequisite for multicellularity) showing evidence of motility (PNAS 2019) go back to at least 2.1 billion years ago, almost to the beginning of the Proterozoic Eon. The fossils were investigated by an international team of scientists, led by Pr. A. El Albani of the University of Poitiers, France.

    On the surface, the fossils resemble irregularly shaped cookies with split edges and a lumpy interior. Viewed in a high-resolution X-ray tomograph (a kind of CAT scan) they reveal different shape and size exhibiting elongate, circular and a sheet-like structure with a pervading radial fabric and a neat pattern of central folds. This structure is too complex to be a product of inorganic processes, and further analyses confirmed that the carbon in the fossilized tissue was assembled by biological processes, also that the iron-sulfide mineral pyrite replacing most of the tissue had been formed by bacteria “breathing” sulfate, rather than oxygen, when decomposing the organisms in the sediment. Finally, the organisms were shown to have lived in shallow marine waters with free oxygen.

    Large size generally signifies an energy-demanding way of life. Breathing oxygen, as we do, is a much more efficient way of obtaining energy than other physiological processes. The Proterozoic Eon saw two major events of oxygen build-up in the atmosphere (and, thereby, in the oceans); the first near the beginning of the Eon, 2.45–2.2 billion years ago, and the second at the end, 0.8–0.54 billion years ago. The evolution of the Gabon fossils, representing an early step toward large-sized multicellularity, may have become possible by the first boost in oxygen, whereas the “Cambrian explosion” could have been fueled by the second. Why it took around 1.5 billion years for the multicellular organisms to take over is currently one of the great unsolved mysteries in the history of the biosphere.