GLOW: Loss of volatiles from the Hadean Earth and the redox evolution of the early atmosphere

一些研究人员认为，像地球这样的岩石行星一定是由巨大的撞击形成的，而对地球的最后一次撞击导致了月球的形成。在这次撞击之后，早期的地球可能经历了残留的星子的持续轰击。这些轰击被称为晚期吸积撞击，其中一些可能和月球一样大。巨大的撞击和晚期的吸积撞击都是非常有能量的。它们中的每一个都能融化大部分的地幔，表面温度可高达5000 - 15000 K。如此热的表面将有助于大气逃逸到太空，这对早期地球的表面环境很重要。最轻的元素——氢——在这个过程中最容易被去除，所以在地表水存在的情况下，撞击导致的大气损失可能导致地球氧化。这种灾难性蒸发的概念在系外行星领域被普遍接受，但在地球科学中还没有得到关注。这项研究将结合系外行星大气文献中发展起来的新思想来研究冥古宙地球（地球历史的前5亿年）。大气的氧化还原状态对地球上生命的出现也很重要。因此，我们对高能撞击后地球演化的建模可以为那些目前正在探索系外行星寻找生命迹象的人提供及时的参考框架。该项目将支持博士后研究人员，并通过指导纽黑文科学博览会高中学生做出更广泛的贡献。大多数关于地球早期大气中挥发物去除的研究集中在1500-2500 K的狭窄温度范围内，此时质量损失效率低，并且受到湍流顶上方扩散的限制。高能撞击后的极端热条件将在几百年内迅速消散，但即使在这么短的时间内，大气损失也可能相当于地球上几个海洋的量级。拟议的研究旨在量化早期地球的这一极端时期，通过对地球撞击后的大气进行流体动力学模拟，将内部热量和来自太阳的入射x射线和紫外线辐射结合起来。因为地球早期的大气会与地下的岩浆海洋发生化学反应，所以大气的演化会影响地幔的氧化还原演化。将探索相关的参数空间，以评估冥古宙地球的不同进化路径如何符合现有的地质数据，以及文献中提出的其他理论可能性。这将对冥古宙地球的特性提供前所未有的深入了解，并由此揭示挥发物的损失可能是解释地球为何在太阳系行星中独一无二的缺失纽带。该提案是根据DCL 22-032: Dear Colleague Letter: Geoscience Lessons for and from Other Worlds （GLOW）提交给CH的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Some researchers think rocky planets like Earth must have formed by giant impacts, and that the last of such impacts to Earth resulted in the formation of the Moon. After this impact, the early Earth likely experienced continued bombardment of leftover planetesimals. These bombardments are called late accretion impacts, some of which could be as large as the Moon. Both giant impacts and late accretion impacts are very energetic. Each of them can melt a large fraction of Earth’s mantle, and the surface can be as hot as 5,000-15,000 K. Such a hot surface would help the atmosphere escape to space, which is important for the surface environments of the early Earth. The lightest element - hydrogen - is most easily removed by this process, so in the presence of surface water the impact-driven atmospheric loss could result in the oxidation of Earth. The notion of such catastrophic evaporation is generally accepted in the exoplanet field, but it has not gained traction in the Earth sciences. This research will incorporate novel ideas developed in the exoplanet atmospheric literature to the study of the Hadean Earth (the first 500 million years of Earth history). The redox state of the atmosphere is also important for the emergence of life on Earth. Thus, our modeling of Earth evolution in the aftermath of high-energy impacts could provide a timely reference frame for those currently exploring exoplanets for signs of life. This project will support a postdoctoral researcher and contribute more broadly through mentoring New Haven Science Fair high school students.Most research on the removal of volatiles from Earth’s early atmosphere focuses on a narrow temperature range of 1500–2500 K when mass loss is inefficient and limited by diffusion above the turbopause. The extreme thermal conditions right after high-energy impacts would quickly dissipate in a few hundred years, but even in this short period, the atmospheric loss can be on the order of several Earth oceans. The proposed research aims to quantify this extreme period of the early Earth, by conducting a fluid dynamical simulation of Earth’s post-impact atmosphere that incorporates the interior heat and the incoming X-ray and ultraviolet irradiation from our Sun. Because Earth’s early atmosphere would chemically interact with the magma ocean below, the evolution of the atmosphere will influence the redox evolution of the mantle. The relevant parameter space will be explored to assess how the different evolutionary pathways of the Hadean Earth comply with available geological data, and with other theoretical possibilities suggested in the literature. This will provide an unprecedented insight into the properties of the Hadean Earth and, in doing so, reveal how the loss of volatiles may be the missing nexus that explains why Earth is unique among the planets in our solar system. This proposal was submitted to CH in response to DCL 22-032: Dear Colleague Letter: Geoscience Lessons for and from Other Worlds (GLOW).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.