Xenon: King of the Gases
When: April 16, 2019 3PM PDT
Xenon is the heaviest gas in the atmosphere, yet it is also, next to helium, the gas for which there is the greatest evidence of escape to space. Trapped gases in old rocks indicate that Xe escape occurred throughout the first half of Earth’s history. Here we discuss how Xe can preferentially escape from Earth as an ion, which maps to constraints on the hydrogen abundance in Earth’s ancient atmosphere. We find that hydrogen (or methane) mixing ratios must have exceeded 1% for Xe to escape. We conclude that hydrogen (or methane) was a major gas in Earth’s atmosphere at times through the first half of Earth’s history —- although not persistently —- and that Earth probably lost the hydrogen from an ocean of water before embarking on the Neoproterozoic 2.4 billion years ago.