火星早期阶段性变暖、氧化和地球化学转变的耦合模式
A coupled model of episodic warming, oxidation and geochemical transitions on early Mars
摘要：
用大气演化模型来描述火星的地质仍然是一个重大挑战。火星地质学的特点是，过去的证据表明，表面存在间歇性的液态水，地球化学表明，从潮湿到干燥和氧化性更强的表面条件缓慢而间歇地过渡。在这里，我们提出了一个新的模型，将减少温室气体和氧化由于氢逃逸的随机注射，调查这些不同的意见负责的条件。我们发现，火星在其早期历史中可能反复地从还原（富含H2）过渡到氧化（富含O2）的大气条件。我们的模型预测了一个普遍寒冷的早期火星，年平均温度低于240 K。如果峰值还原气体释放率和背景CO2水平足够高，它仍然表现出足够的阶段性温暖间隔，以降解火山口壁，形成山谷网络，并创造其他河流/湖泊特征。我们的模型还预测了大气中O2的瞬时积累，这有助于解释盖尔陨石坑中锰氧化物等氧化矿物的发生。我们认为，明显的Noachian-Hesperian过渡页硅酸盐沉积到硫酸盐沉积约35亿年前可以解释为一个综合的结果，增加行星氧化，减少地下水的可用性和不断减弱的火流星撞击通量，这大大减缓了表面硫酸盐的再活化和热化学破坏。最终，火星早期气候和表面化学的快速和重复变化将为任何新兴的微生物生命带来挑战和机遇。
英文摘要：
Reconciling the geology of Mars with models of atmospheric evolution remains a major challenge. Martian geology is characterized by past evidence for episodic surface liquid water, and geochemistry indicating a slow and intermittent transition from wetter to drier and more oxidizing surface conditions. Here we present a new model incorporating randomized injection of reducing greenhouse gases and oxidation due to hydrogen escape, to investigate the conditions responsible for these diverse observations. We find that Mars could have transitioned repeatedly from reducing (H2-rich) to oxidizing (O2-rich) atmospheric conditions in its early history. Our model predicts a generally cold early Mars, with mean annual temperatures below 240 K. If peak reducing gas release rates and background CO2 levels are high enough, it nonetheless exhibits episodic warm intervals sufficient to degrade crater walls, form valley networks and create other fluvial/lacustrine features. Our model also predicts transient buildup of atmospheric O2, which can help explain the occurrence of oxidized mineral species such as manganese oxides at Gale Crater. We suggest that the apparent Noachian--Hesperian transition from phyllosilicate deposition to sulfate deposition around 3.5 billion years ago can be explained as a combined outcome of increasing planetary oxidation, decreasing groundwater availability and a waning bolide impactor flux, which dramatically slowed the remobilization and thermochemical destruction of surface sulfates. Ultimately, rapid and repeated variations in Mars' early climate and surface chemistry would have presented both challenges and opportunities for any emergent microbial life.
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