Each year, about 2 kg of helium-3, a rare isotope of helium gas, escapes from Earth’s interior, mostly along the mid-ocean ridge system. Helium-3 is primordial, created shortly after the Big Bang and acquired from the Solar Nebula as the Earth formed. Geochemical evidence indicates the Earth has deep reservoirs of helium-3, but their locations and abundances remain uncertain. New models of volatile exchange during Earth’s formation and evolution...
