Sorbonne Université, CNRS, Muséum National d'Histoire Naturelle, Institut de Minéralogie, de Physique des matériaux et de Cosmochimie, UMR7590, Paris, France.
Université de Bordeaux, CNRS, LP2i Bordeaux, UMR5797, Gradignan, France.
Nature. 2022 Jun;606(7915):713-717. doi: 10.1038/s41586-022-04710-4. Epub 2022 Jun 22.
Our understanding of atmosphere formation essentially relies on noble gases and their isotopes, with xenon (Xe) being a key tracer of the early planetary stages. A long-standing issue, however, is the origin of atmospheric depletion in Xe and its light isotopes for the Earth and Mars. Here we report that feldspar and olivine samples confined at high pressures and high temperature with diluted Xe and krypton (Kr) in air or nitrogen are enriched in heavy Xe isotopes by +0.8 to +2.3‰ per AMU, and strongly enriched in Xe over Kr. The upper +2.3‰ per AMU value is a minimum because quantitative trapping of unreacted Xe, either in bubbles or adsorbed on the samples, is likely. In light of these results, we propose a scenario solving the missing Xe problem that involves multiple magma ocean stage events at the proto-planetary stage, combined with atmospheric loss. Each of these events results in trapping of Xe at depth and preferential retention of its heavy isotopes. In the case of the Earth, the heavy Xe fraction was later added to the secondary CI chondritic atmosphere through continental erosion and/or recycling of a Hadean felsic crust.
我们对大气形成的理解主要依赖于稀有气体及其同位素，氙（Xe）是早期行星阶段的关键示踪剂。然而，一个长期存在的问题是地球和火星上 Xe 及其轻同位素大气损耗的起源。在这里，我们报告说，在高压和高温下与空气中或氮气中的稀释 Xe 和氪（Kr）一起封存的长石和橄榄石样品，每质量单位（AMU）增加+0.8 到+2.3‰，并且 Xe 相对于 Kr 强烈富集。上限+2.3‰/AMU 是一个最小值，因为未反应的 Xe 很可能定量地被困在气泡或样品上。鉴于这些结果，我们提出了一个解决缺失 Xe 问题的方案，该方案涉及原行星阶段的多个岩浆海洋阶段事件，以及大气损失。这些事件中的每一个都导致 Xe 在深处被捕获，并且其重同位素被优先保留。就地球而言，重 Xe 部分后来通过大陆侵蚀和/或 Hadean 长英质地壳的再循环而添加到次生 CI 球粒陨石大气中。
