Unité Mixte de Recherche (UMR), Centre National de la Recherche Scientifique (CNRS), IC2MP 7285, University of Poitiers, 86073 Poitiers, France;
Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK S7N 5A5, Canada.
Proc Natl Acad Sci U S A. 2019 Feb 26;116(9):3431-3436. doi: 10.1073/pnas.1815721116. Epub 2019 Feb 11.
Evidence for macroscopic life in the Paleoproterozoic Era comes from 1.8 billion-year-old (Ga) compression fossils [Han TM, Runnegar B (1992) 257:232-235; Knoll et al. (2006) 361:1023-1038], Stirling biota [Bengtson S et al. (2007) 33:351-381], and large colonial organisms exhibiting signs of coordinated growth from the 2.1-Ga Francevillian series, Gabon. Here we report on pyritized string-shaped structures from the Francevillian Basin. Combined microscopic, microtomographic, geochemical, and sedimentologic analyses provide evidence for biogenicity, and syngenicity and suggest that the structures underwent fossilization during early diagenesis close to the sediment-water interface. The string-shaped structures are up to 6 mm across and extend up to 170 mm through the strata. Morphological and 3D tomographic reconstructions suggest that the producer may have been a multicellular or syncytial organism able to migrate laterally and vertically to reach food resources. A possible modern analog is the aggregation of amoeboid cells into a migratory slug phase in cellular slime molds at times of starvation. This unique ecologic window established in an oxygenated, shallow-marine environment represents an exceptional record of the biosphere following the crucial changes that occurred in the atmosphere and ocean in the aftermath of the great oxidation event (GOE).
太古宙时期宏观生命的证据来自于 18 亿年前的压缩化石[Han TM,Runnegar B(1992)257:232-235;Knoll 等人(2006)361:1023-1038],Stirling 生物群[Bengtson S 等人(2007)33:351-381],以及来自加蓬 21 亿年前 Francevillian 系列的大型殖民地生物体,这些生物体表现出协调生长的迹象。在这里,我们报告了来自 Francevillian 盆地的黄铁矿化的串状结构。结合微观、微断层扫描、地球化学和沉积学分析,为其生物起源、同生性提供了证据,并表明这些结构在靠近沉积-水界面的早期成岩作用过程中发生了化石化。串状结构的直径可达 6 毫米,在地层中延伸可达 170 毫米。形态和 3D 断层扫描重建表明,生产者可能是一种多细胞或合胞体生物,能够横向和纵向迁移以获取食物资源。一个可能的现代类比是在细胞黏菌因饥饿而聚集变形虫细胞进入迁移阶段。在大氧化事件(GOE)后大气和海洋发生关键变化后,这种在富氧浅海环境中建立的独特生态窗口代表了生物圈的一个特殊记录。