A coupled model of episodic warming, oxidation and geochemical transitions on early Mars
A coupled model of episodic warming, oxidation and geochemical transitions on early Mars
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DOI：
10.1038/s41561-021-00701-8
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发表时间：
2021-03-01
影响因子：
18.3
通讯作者：
Steakley, Kathryn
中科院分区：
文献类型：
--
作者：
Wordsworth, Robin;Knoll, Andrew H.;Steakley, Kathryn
将火星地质与大气演化模型相协调仍然是一项重大挑战。火星地质的特点是，过去有证据表明火星表面有偶发的液态水，而地球化学表明火星表面条件从湿润到干燥和氧化性更强的缓慢而间歇性的转变。在这里，我们提出了一个模型，其中包括随机注入减少温室气体和氢逸氧化，以研究导致这些不同观测结果的条件。我们发现火星可能在其早期历史中反复地从还原性（富氢）大气条件过渡到氧化性（富氧）大气条件。我们的模型预测火星早期普遍寒冷，年平均气温低于240摄氏度。如果峰值还原气体释放率和背景二氧化碳水平足够高，它仍然会显示出足以降解火山口壁、形成山谷网络和创造其他河流/湖泊特征的间歇性温暖间隔。我们的模型还预测了大气中氧的短暂积累，这有助于解释盖尔陨石坑中氧化矿物的出现，比如锰的氧化物。我们认为，35亿年前从层状硅酸盐沉积到硫酸盐沉积的诺亚纪-希斯纪明显转变可以解释为行星氧化增加、地下水可用性减少和撞击物通量减弱的综合结果，这大大减缓了地表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反复变化将为任何新兴的微生物生命带来挑战和机遇。
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 model that incorporates 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 (hydrogen-rich) to oxidizing (oxygen-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 carbon dioxide 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 build-up of atmospheric oxygen, 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's early climate and surface chemistry would have presented both challenges and opportunities for any emergent microbial life.