The search for signs of life in the ancient rock record, extreme terrestrial environments, and other planetary bodies requires a well-established, universal, and unambiguous test of biogenicity. This is notably true for cellular remnants of microbial life, since their relatively simple morphologies resemble various abiogenic microstructures that occur in nature. Although lists of qualitative biogenicity criteria have been devised, debates regarding the biogenicity of many ancient microfossils persist to this day. We propose here an alternative quantitative approach for assessing the biogenicity of putative microfossils. In this theoretical approach, different hypotheses—involving biology or not and depending on the geologic setting—are put forward to explain the observed objects. These hypotheses correspond to specific types of microstructures/systems. Using test samples, the morphology and/or chemistry of these systems are then characterized at the scale of populations. Morphologic parameters include, for example, circularity, aspect ratio, and solidity, while chemical parameters could include elementary ratios (e.g., N/C ratio), isotopic enrichments (e.g., δ13C), or chirality (e.g., molar proportion of stereoisomers), among others. Statistic trends distinguishing the different systems are then searched for empirically. The trends found are translated into “decision spaces” where the different systems are quantitatively discriminated and where the potential microfossil population can be located as a single point. This approach, which is formulated here on a theoretical level, will solve several problems associated with the classical qualitative criteria of biogenicity. Most importantly, it could be applied to reveal the existence of cellular life on other planets, for which characteristics of morphology and chemical composition are difficult to predict.

中文翻译：

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评估生物源性的替代方法

在古代岩石记录、极端陆地环境和其他行星体中寻找生命迹象需要对生物成因进行完善、普遍和明确的测试。对于微生物生命的细胞残余物来说尤其如此，因为它们相对简单的形态类似于自然界中存在的各种非生物微结构。尽管已经制定了定性生物源标准清单，但关于许多古代微化石的生物源性的争论一直持续到今天。我们在这里提出了一种替代的定量方法来评估假定的微化石的生物源性。在这种理论方法中，提出了不同的假设——是否涉及生物学以及取决于地质环境——来解释观察到的物体。这些假设对应于特定类型的微结构/系统。使用测试样品，这些系统的形态和/或化学特性然后在种群规模上进行表征。形态参数包括例如圆度、纵横比和密实度，而化学参数可能包括基本比例（例如，N/C 比率）、同位素富集（例如，δ13C）或手性（例如，立体异构体的摩尔比例）等。然后根据经验搜索区分不同系统的统计趋势。发现的趋势被转化为“决策空间”，其中不同的系统被定量区分，潜在的微化石种群可以作为一个点定位。这种方法是在理论水平上制定的，将解决与经典的生物源性定性标准相关的几个问题。最重要的是，它可以用于揭示其他行星上是否存在细胞生命，这些行星的形态和化学成分特征难以预测。