Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
Now at Institute of Earth Sciences, University of Lausanne, Lausanne, Switzerland.
Sci Rep. 2019 Nov 13;9(1):16712. doi: 10.1038/s41598-019-53272-5.
Hydrothermal and metamorphic processes could have abiotically produced organo-mineral associations displaying morphological and isotopic characteristics similar to those of fossilized microorganisms in ancient rocks, thereby leaving false-positive evidence for early life in the geological record. Recent studies revealed that geologically-induced alteration processes do not always completely obliterate all molecular information about the original organic precursors of ancient microfossils. Here, we report the molecular, geochemical, and mineralogical composition of organo-mineral associations in a chert sample from the ca. 3.47 billion-year-old (Ga) Mount Ada Basalt, in the Pilbara Craton, Western Australia. Our observations indicate that the molecular characteristics of carbonaceous matter are consistent with hydrothermally altered biological organics, although significantly distinct from that of organic microfossils discovered in a chert sample from the ca. 3.43 Ga Strelley Pool Formation in the same area. Alternatively, the presence of native metal alloys in the chert, previously believed to be unstable in such hydrothermally influenced environments, indicates strongly reducing conditions that were favorable for the abiotic formation of organic matter. Drawing definitive conclusions about the origin of most Paleoarchean organo-mineral associations therefore requires further characterization of a range of natural samples together with experimental simulations to constrain the molecular composition and geological fate of hydrothermally-generated condensed organics.
热液和变质作用可能会产生无生命的有机-矿物组合，这些组合具有与古代岩石中化石微生物相似的形态和同位素特征，从而在地质记录中留下了早期生命的虚假阳性证据。最近的研究表明，地质诱导的蚀变过程并不总是完全消除古代微生物化石原始有机前体的所有分子信息。在这里，我们报告了来自西澳大利亚皮尔巴拉克拉通约 34.7 亿年（Ga）阿达山玄武岩的燧石样本中有机-矿物组合的分子、地球化学和矿物学组成。我们的观察表明，碳质物质的分子特征与热液改变的生物有机物一致，尽管与同一地区约 34.3 Ga 斯特雷利池组燧石样本中发现的有机微化石有明显区别。或者，在以前被认为在这种热液影响的环境中不稳定的燧石中存在天然金属合金，这强烈表明存在有利于有机物质无生命形成的强还原条件。因此，要对大多数古太古代有机-矿物组合的起源得出明确结论，需要对一系列天然样品进行进一步的特征描述，并进行实验模拟，以限制热液产生的浓缩有机物的分子组成和地质命运。
