Earth is a volatile-rich planet. Volatile elements have played an important role in the geological evolution of Earth and were also responsible for creating habitable environments, where life could evolve and be sustained. Earth accreted within the protoplanetary disk inside the snowline, where the surrounding environment was too hot for volatiles to condense during accretion. However, Earth could have accreted volatiles by capture of nebular gases in the early magma ocean stage or from asteroids and comets that formed beyond the snow line impacting Earth early on in the accretion process. Otherwise, Earth could have accreted dry with its volatiles delivered by asteroidal or cometary impacts much later in its history, after the dissipation of the protosolar nebula. The exact sources of Earth’s volatiles and how and when they were delivered have remained uncertain. Chondritic meteorites, made of primitive materials that escaped differentiation, are thought to be one such source of volatiles on the terrestrial planets.
To constrain the source and timing of Earth’s volatile delivery, scientists seek to sample the deepest and most pristine parts of Earth’s interior. Mantle plumes, like those below massive volcanoes such as Yellowstone, are upwellings of hot material from thousands of kilometer deep regions within the Earth. A recent study led by Michael Broadley from the Centre de Recherches Pétrographiques et Géochimiques (CNRS and Université de Lorraine, France) and colleagues analyzed the isotopic compositions of noble gases from the Yellowstone volcano. The study found that krypton and xenon isotopic compositions in Yellowstone volcanic gases derived from the deep mantle are, in fact, similar to those of chondritic meteorites. These isotopic compositions are also similar to those of noble gases from mid-ocean ridge basalts sourced from the upper mantle. Therefore, this research suggests that Earth may have largely retained chondritic volatiles from impacts during the earliest stages of accretion and did not rely completely upon volatile delivery via later impacts. READ MORE