Watanabe Y, Martini J E, Ohmoto H
Astrobiology Research Center and Department of Geosciences, The Pennsylvania State University, University Park 16802, USA.
Nature. 2000 Nov 30;408(6812):574-8. doi: 10.1038/35046052.
Microorganisms have flourished in the oceans since at least 3.8 billion years (3.8 Gyr) ago, but it is not at present clear when they first colonized the land. Organic matter in some Au/U-rich conglomerates and ancient soils of 2.3-2.7 Gyr age has been suggested as remnants of terrestrial organisms. Some 2.7-Gyr-old stromatolites have also been suggested as structures created by terrestrial organisms. However, it has been disputed whether this organic matter is indigenous or exogenic, and whether these stromatolites formed in marine or fresh water. Consequently, the oldest undisputed remnants of terrestrial organisms are currently the 1.2-Gyr-old microfossils from Arizona, USA. Unusually carbonaceous ancient soils--palaeosols--have been found in the Mpumalanga Province (Eastern Transvaal) of South Africa. Here we report the occurrences, elemental ratios (C, H, N, P) and isotopic compositions of this organic matter and its host rocks. These data show that the organic matter very probably represents remnants of microbial mats that developed on the soil surface between 2.6 and 2.7 Gyr ago. This places the development of terrestrial biomass more than 1.4 billion years earlier than previously reported.
至少从38亿年前起，微生物就在海洋中大量繁殖，但目前尚不清楚它们最初何时开始在陆地上定殖。有人认为，在一些富含金/铀的砾岩和年龄在23亿至27亿年的古老土壤中的有机物是陆地生物的残余物。一些27亿年前的叠层石也被认为是由陆地生物形成的结构。然而，这些有机物是原生的还是外源的，以及这些叠层石是在海洋还是淡水中形成，一直存在争议。因此，目前无可争议的最古老的陆地生物残余物是来自美国亚利桑那州的12亿年前的微化石。在南非姆普马兰加省（东德兰士瓦）发现了异常富含碳的古老土壤——古土壤。在此，我们报告这种有机物及其寄主岩石的出现情况、元素比率（碳、氢、氮、磷）和同位素组成。这些数据表明，这些有机物很可能代表了26亿至27亿年前在土壤表面形成的微生物垫的残余物。这使得陆地生物量的出现时间比之前报道的早了14亿多年。
