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A coupled model of episodic warming, oxidation and geochemical transitions on early Mars
Nature Geoscience ( IF 18.3 ) Pub Date : 2021-03-08 , DOI: 10.1038/s41561-021-00701-8
Robin Wordsworth , Andrew H. Knoll , Joel Hurowitz , Mark Baum , Bethany L. Ehlmann , James W. Head , Kathryn Steakley

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.



中文翻译:

早期火星偶发性变暖、氧化和地球化学转变的耦合模型

协调火星地质与大气演化模型仍然是一项重大挑战。火星地质学的特点是过去有证据表明地表液态水偶发性,而地球化学表明从潮湿到干燥和氧化性更强的地表条件缓慢而间歇地过渡。在这里,我们提出了一个模型,该模型结合了减少温室气体的随机注入和由于氢气逸出引起的氧化,以研究导致这些不同观察的条件。我们发现,火星在其早期历史中可能已经从还原(富氢)大气条件反复转变为氧化(富氧)大气条件。我们的模型预测早期火星普遍寒冷,年平均温度低于 240 K。如果峰值还原气体释放率和背景二氧化碳水平足够高,尽管如此,它仍表现出间歇性的温暖间隔,足以使火山口壁退化,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氧气的瞬时积累,这可以帮助解释在盖尔陨石坑出现氧化的矿物物种,如锰氧化物。我们认为,大约 35 亿年前从页硅酸盐沉积到硫酸盐沉积的明显 Noachian-Hesperian 转变可以解释为行星氧化增加、地下水可用性降低和火流星撞击通量减弱的综合结果,这显着减缓了再活动和热化学破坏表面硫酸盐。最终,

更新日期:2021-03-08
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