The ultraviolet history of the terrestrial planets - implications for biological evolution
The ultraviolet history of the terrestrial planets - implications for biological evolution
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DOI：
10.1016/s0032-0633(99)00087-2
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发表时间：
2000-02-01
影响因子：
2.4
通讯作者：
Cockell, CS
中科院分区：
文献类型：
--
作者：
Cockell, CS
利用辐射传输模型研究了地球、火星和金星从4.5 Ga至今的比较表面紫外线辐射历史，从而研究了它们的比较理论光生物学历史。地球可能开始于缺氧太古宙期间紫外线辐射通量较高的时期。在元古代早期，紫外线通量随着氧分压的下降而下降，因此臭氧柱丰度上升，但臭氧柱受到随机消耗事件的影响，主要是由撞击事件和可能的大规模火山活动以及较少发生的近距离宇宙事件（如超新星）引起的。相比之下，火星的历史主要是太阳光度的缓慢增加和二氧化碳分压的降低，这两者都导致了紫外线通量的增加。金星的紫外线辐射历史一直是由温室效应主导的，通过温室效应，二氧化碳的高分压使金星表面的紫外线辐射环境变得恶劣。这些不同的历史影响了三颗行星潜在的比较进化光生物学。在地球上，生命从对紫外线辐射的耐受性，特别是对暴露在紫外线下的生物体来说，一定很高的太古宙过渡到一个光生物学更温和的时代。在后一个时代，主要的进化选择压力是允许容忍UVB辐射突然和不可预测的增加，超过由外源臭氧柱扰动引起的季节性和日最大值。以火星为例，紫外线辐射通量随着时间的推移而增加。今天对DNA的生物有效辐照度与太古宙地球的辐照度没有太大的不同。如果这颗行星遭受了大气崩溃，那么它可能在过去的某个时刻受到紫外线危机的影响，那时dna加权辐照度将增加三到五倍。金星在后期轰击后不久就过渡到光生物学的温和时期。火星和金星上没有生命的表面，前者的dna加权辐照度并不比太古代的地球大多少，后者则微不足道，这证明了当其他物理因素，特别是缺乏液态水，限制了生命时，紫外线辐射作为一种进化选择压力的重要性并不大。了解类地行星表面紫外线通量的比较进化差异，可以帮助我们了解紫外线辐射对确定它们在过去不同阶段是否适合生命居住的影响和缺乏影响。(C) 2000 Elsevier Science Ltd.版权所有。
A radiative transfer model is employed to investigate the comparative surface ultraviolet (UV) radiation histories of Earth, Mars and Venus from 4.5 Ga to the present and thus their comparative theoretical photobiological histories. Earth probably began with a period of higher ultraviolet radiation fluxes during the anoxic Archean. During the early Proterozoic UV fluxes declined as oxygen partial pressures and thus ozone column abundance rose, but the ozone column became subject to stochastic depletion events caused principally by impact events and possibly large-scale volcanism and less frequently, close cosmic events such as supernovae. In contrast Mars has been subject to a history dominated by a slow increase in solar luminosity and a reduction in partial pressures of CO2, both of which have resulted in an increase in UV flux. The UV radiation history of Venus has been dominated by the greenhouse effect through which high partial pressures of CO2 made the surface UV radiation environment clement. These distinct histories influence the potential comparative evolutionary photobiology of the three planets. On Earth, life transitioned from the Archean, when tolerance to UV radiation, particularly for exposed organisms, must have been high to a more photobiologically clement era. In this latter era the predominant evolutionary selection pressure is one that allows for tolerance of sudden and unpredictable increases in UVB radiation above seasonal and diurnal maxima caused by exogenous perturbation of the ozone column. In the case of Mars, the UV radiation flux has increased over time. Today the biologically effective irradiances to DNA are not considerably different from those that are calculated for Archean Earth. If the planet suffered an atmospheric collapse then it may have been subject to an ultraviolet crisis at some point in its past when DNA-weighted irradiance would have increased three to five-fold. Venus transitioned into a photobiologically clement era soon after late bombardment. The lifeless surfaces of Mars and Venus, when in the former case DNA-weighted irradiances are not much greater than Archean Earth and in the latter case, insignificant, are testament to the unimportance of UV radiation as an evolutionary selection pressure when other physical factors, particularly lack of liquid water, become limiting to life. Understanding the comparative evolutionary differences in surface UV flux of the terrestrial planets can help us understand the influence, and lack of influence, of UV radiation in determining their suitability as abodes for life at different stages in their past. (C) 2000 Elsevier Science Ltd. All rights reserved.