arXiv 1104.43222011-04astro-ph.EPastro-ph.CO

论银河系生命的起源与演化

On the Origin and Evolution of Life in the Galaxy

Michael McCabe, Holly Lucas

备注：: See http://www.astrobiologysociety.org/index.php
发表信息：: International Journal of Astrobiology 9 (4) : 217-226 Cambridge University Press (2010)
DOI：: 10.1017/S1473550410000340

摘要：

一个简单的随机进化模型，基于需要通过一系列的n个关键步骤（卡特1983年，沃森2008年）适用于地球和外星生命的起源。在前一种情况下，人类在地球可居住时期出现的时间表明n = 4。逐步增加早期的进化转变（Maynard Smith和Szathmary，1995）给出了n = 5时的最佳拟合，这意味着它们的初始转变不是关键的，或者可居住性开始于大约6 Ga前。后一种情况排除了火星或太阳系其他地方的生命起源，简单的人择论证是，宇宙中地外生命是稀缺的，因为它没有时间进化。或者，如果基本的祖细胞物质迁移到地球是可能的，时间尺度可以延长。如果模型中包含额外的过渡以允许地球迁移，那么可居住性的开始甚至需要早于6 Ga前。我们目前对银河系可居住性和动力学的理解并不排除这种可能性。我们的结论是，银河系间断平衡（Cirkovic et al. 2009），提出作为一种方法绕过人择问题，不是唯一的方法，使生命在银河系中更普遍。

英文摘要：

A simple stochastic model for evolution, based upon the need to pass a sequence of n critical steps (Carter 1983, Watson 2008) is applied to both terrestrial and extraterrestrial origins of life. In the former case, the time at which humans have emerged during the habitable period of the Earth suggests a value of n = 4. Progressively adding earlier evolutionary transitions (Maynard Smith and Szathmary, 1995) gives an optimum fit when n = 5, implying either that their initial transitions are not critical or that habitability began around 6 Ga ago. The origin of life on Mars or elsewhere within the Solar System is excluded by the latter case and the simple anthropic argument is that extraterrestrial life is scarce in the Universe because it does not have time to evolve. Alternatively, the timescale can be extended if the migration of basic progenotic material to Earth is possible. If extra transitions are included in the model to allow for Earth migration, then the start of habitability needs to be even earlier than 6 Ga ago. Our present understanding of Galactic habitability and dynamics does not exclude this possibility. We conclude that Galactic punctuated equilibrium (Cirkovic et al. 2009), proposed as a way round the anthropic problem, is not the only way of making life more common in the Galaxy.

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