During the Noachian period, 4.1-3.7 Gys ago, the Martian environment was moderately similar to the one on present Earth. Liquid water was widespread in a neutral environment, volcanic activity and heat flow more vigorous, and atmospheric pressure and temperature were higher than today. These conditions may have favoured the spread of life on the surface of Mars. The recognition that different planets and moons share rocky material cast in space by meteoroid impact entails that life creation is not necessary for each single planetary body, but could travel through the Solar system on board of rock fragments. Studies conducted on the past forms of Martian life have already highlighted possible positive matches with microbialite-like structures, referable to the geo-environmental conditions in the Noachian and Hesperian. However, by necessity, these studies are on predominantly micro and meso-scopic scale structures and doubts arise as to their attribution to the biogenic world. We suggest that in the identification of Martian life, we are currently in a position similar to the one of Kalkowsky who in 1908, based solely on morphological and sedimentological arguments, hypothesized the (now accepted) view of the biotic origin of stromatolites. Our analysis of thousands of images from Spirit, Opportunity and Curiosity has provided a selection of images of ring-shaped, domal and coniform macrostructures that resemble terrestrial microbialites such as the ring-shaped stromatolites of Lake Thetis, and stacked cones reminiscent of the group of terrestrial Conophyton. Notably, the latter were detected by Curiosity in the mudstone known as ‘Sheepbed’, the same outcrop where past organic molecules have been detected and where the occurrence of microbial-induced sedimentary structures (MISS) and of many more microbialitic micro, meso and macrostructures has already been hypothesized. Some of the structures discussed in this work are so complex that alternative biological hypotheses can be formulated as possible algae. Alternate, non-abiotic explanations are examined but we find difficult to explain some of such structures in the context of normal sedimentary processes, both syngenetic or epigenetic.

中文翻译：

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为什么地球上使用的地质标准对火星也无效？已灭绝的火星湖泊中可能存在微生物和藻类的证据

在 4.1-3.7 Gys 之前的 Noachian 时期，火星环境与现在地球上的环境有适度相似。液态水在中性环境中广泛分布，火山活动和热流更加剧烈，大气压力和温度都高于今天。这些条件可能有利于火星表面的生命传播。认识到不同的行星和卫星共享由流星体撞击在太空中形成的岩石物质，这意味着生命的创造并不是每个行星体都必需的，而是可以在岩石碎片上穿越太阳系。对火星生命过去形式的研究已经强调了与类似微生物结构的可能正匹配，这与诺亚和赫斯珀里亚的地理环境条件有关。然而，必要时，这些研究主要是关于微观和中观尺度的结构，人们怀疑它们是否属于生物世界。我们建议，在火星生命的鉴定中，我们目前处于类似于 Kalkowsky 的立场，他在 1908 年仅基于形态学和沉积学论据，假设了（现在已被接受的）叠层石生物起源的观点。我们对来自 Spirit、Opportunity 和 Curiosity 的数千张图像的分析提供了一系列类似于陆地微生物的环状、圆顶和锥形宏观结构图像，例如 Thetis 湖的环状叠层石，以及让人想起陆地的 我们建议，在火星生命的鉴定中，我们目前处于类似于 Kalkowsky 的立场，他在 1908 年仅基于形态学和沉积学论据，假设了（现在已被接受的）叠层石生物起源的观点。我们对来自 Spirit、Opportunity 和 Curiosity 的数千张图像的分析提供了一系列类似于陆地微生物的环状、圆顶和锥形宏观结构图像，例如 Thetis 湖的环状叠层石，以及让人想起陆地的 我们建议，在火星生命的鉴定中，我们目前处于类似于 Kalkowsky 的立场，他在 1908 年仅基于形态学和沉积学论据，假设了（现在已被接受的）叠层石生物起源的观点。我们对来自 Spirit、Opportunity 和 Curiosity 的数千张图像的分析提供了一系列类似于陆地微生物的环状、圆顶和锥形宏观结构图像，例如 Thetis 湖的环状叠层石，以及让人想起陆地的藻类. 值得注意的是，后者是由好奇号在被称为“Sheepbed”的泥岩中检测到的，在该露头中检测到过去的有机分子，并出现了微生物诱导的沉积结构 (MISS) 以及更多的微生物微观、中观和宏观结构已经被假设了。这项工作中讨论的一些结构非常复杂，以至于可以将替代的生物学假设表述为可能的藻类。检查了替代的非生物解释，但我们发现很难在正常沉积过程的背景下解释一些这样的结构，无论是同生的还是表观的。