The terrestrial biota prior to the origin of land plants (embryophytes): a review of the evidence
The terrestrial biota prior to the origin of land plants (embryophytes): a review of the evidence
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DOI：
10.1111/pala.12172
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发表时间：
2015-07
期刊：
影响因子：
2.6
通讯作者：
C. Wellman;P. Strother
中科院分区：
文献类型：
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作者：
C. Wellman;P. Strother
人们通常认为，在移居陆地之前，生命在海洋中起源并多样化。然而，化学进化模型中的环境限制指出，导致生命起源的关键步骤发生在地面环境中。最早的化石记录不包括陆地沉积物的发现，所以我们对元古代之前陆地微生物覆盖的存在的理解大多是基于推断和地球化学指标，这些指标表明太古宙期间生物圈碳循环。我们的评估是，2.7 Ga时，陆地环境中的微生物生态系统由产氧、光合作用的蓝藻驱动。对现代生物的研究表明，真核生物的起源和初级多样化可能发生在陆地环境中，在2.0 Ga之后不久，但直到1.1 Ga左右才有陆地真核生物的直接化石证据。此时，非海洋栖息地的生物多样性似乎超过了海洋环境，在海洋环境中，硫化物海洋可能损害了真核生物的生理机能并延缓了进化。地球化学指标表明，在850 Ma之前，形成了广泛的土壤微生物覆盖，这一时期大气中氧气的增加可能是由于绿藻向陆地栖息地的进化扩张造成的。显生宙最早陆生生物的直接化石证据包括来自劳伦西亚寒武纪-奥陶纪的有问题的异形。这些结果表明，中奥陶世第一批陆地植物（胚胎植物）的进化发生在一个包括积极适应陆上环境选择的陆生藻类的景观中。
It is often assumed that life originated and diversified in the oceans prior to colonizing the land. However, environmental constraints in chemical evolution models point towards critical steps leading to the origin of life as having occurred in subaerial settings. The earliest fossil record does not include finds from terrestrial deposits, so much of our understanding about the presence of a terrestrial microbial cover prior to the Proterozoic is based on inference and geochemical proxies that indicate biospheric carbon cycling during the Archaean. Our assessment is that by 2.7 Ga, microbial ecosystems in terrestrial settings were driven by oxygen‐generating, photosynthetic cyanobacteria. Studies of modern organisms indicate that both the origin and primary diversification of the eukaryotes could have occurred in terrestrial settings, shortly after 2.0 Ga, but there is no direct fossil evidence of terrestrial eukaryotes until about 1.1 Ga. At this time, it appears that the diversity of life in non‐marine habitats exceeded that found in marine settings where sulphidic seas may have impaired eukaryotic physiology and retarded evolution. Geochemical proxies indicate the establishment of an extensive soil‐forming microbial cover by 850 Ma, and it is possible that a rise in atmospheric oxygen at this time was due to the evolutionary expansion of green algae into terrestrial habitats. Direct fossil evidence of the earliest terrestrial biotas in the Phanerozoic consists of problematical palynomorphs from the Cambro‐Ordovician of Laurentia. These indicate that the evolution of the first land plants (embryophytes) during the Middle Ordovician took place within a landscape that included aeroterrestrial algae which were actively adapting to selection in subaerial settings.