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How are argon and helium added to Earth’s atmosphere through radioactive decay?
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evolution of the atmosphere
A “best guess” reconstruction of the abundance of O2 in Earth's atmosphere as a function of time. The O2 abundance axis is logarithmic.
Argon and helium are added to Earth’s atmosphere through the radioactive decay of elements within the planet's crust and mantle, a process that contributes to the evolution of the atmosphere over geological time.1
- Argon: The vast majority of atmospheric argon is radiogenic, specifically the isotope argon-40. It is produced by the radioactive decay of potassium-40, a common isotope found in rock-forming minerals. As potassium-40 decays, the resulting argon-40 is initially trapped within mineral crystals. It is subsequently released into the atmosphere through igneous activity and the process of outgassing, where gases from the Earth's interior escape to the surface.123
- Helium: Atmospheric helium is primarily the product of the radioactive decay of uranium and thorium. During this decay process, alpha particles—which are the nuclei of helium atoms—are emitted. While some of this helium remains trapped in rocks, a portion is released into the atmosphere. Unlike heavier gases, helium is light enough that some of it eventually escapes Earth's gravitational field into space.14