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【聚焦关键】Oxygen dynamics and early steps towards multicellularity 2.1 billion years ago

2019-12-02

报告题目Oxygen dynamics and early steps towards multicellularity 2.1 billion years ago

报告时间12月04日(星期三)上午10:30

报告地点:天津大学第16教学楼221报告厅

主讲嘉宾Abder El Albani, Professor, Université de Poitiers

报告人简介

     Dr. Abder El Albani是法国Université de Poitiers教授,研究方向为古生物学和沉积地球化学。他带领的研究团队在国际上首次在距今21亿年的古生物化石中发现了多细胞复杂生物的证据,将多细胞生物出现的时间提前了约15亿年,是地球生命演化历程的重大发现,相关成果多次发表在Nature, PNAS等重要期刊上。

报告内容简介

     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.


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