Because of these many modifications, the origins of Earth's volatile elements (hydrogen (water), carbon, nitrogen, and the noble gases) remains enigmatic, and it is difficult to determine if they originated from the solar gas that remained after solar-system formation (the solar nebula) or from differentiated bodies, such as asteroids, which may have collided with a young Earth.
Noble gases are excellent tracers for studying the origins of volatile elements on Earth. Because they are chemically inert, scientists use them to trace physical processes without having to consider the many chemical reactions taking place within Earth's different reservoirs (core, mantle, crust and atmosphere). In a study published in Nature, researchers from the Centre de Recherches Pétrographiques et Géochimiques (CNRS and Université de Lorraine, Nancy, France) and Instituto Nazionale di Geofisica e Vulcanologia (Palermo, Italy) report the results of high-precision noble gas analyses of a CO2-rich mineral spring gas located in the recent volcanic province of Eifel, Germany .
The team, which includes DCO collaborator Bernard Marty (CNRS and Université de Lorraine, Nancy, France), analyzed the isotopic abundances of xenon in CO2-rich gas samples (99.8% CO2). These gases are emitted from gas-rich minerals in the Eifel magmatic region (see photographs). Thanks to advanced purification techniques, the team was able to completely separate xenon from the CO2, allowing them to measure its abundance and isotopic composition with high precision using a state-of-the-art noble gas mass spectrometer.
Left: Victoriaquelle well, Germany. Right: View of the inside of the Victoriaquelle well. The water is agitated by rising bubbles of CO2. Gases are sampled through the funnel, which is plunged into the water and is attached to a sampling tube. The tube is directly connected to pre-evacuated stainless-steel bottles. All photos courtesy of Bernard Marty.
The collected gas samples, directly derived from an underlying magma body, recorded the origin of terrestrial volatiles and the early evolution of our planet. The authors demonstrate that part of the volatile elements trapped in Earth's mantle came from asteroidal material, from planetary bodies whose remnants now reside between Mars and Jupiter. In contrast, noble gases in the atmosphere came from a different cosmochemical source, possibly comets.
The data also point to a deep mantle origin for Eifel volcanism, from a source isolated from whole mantle convection for most of Earth's history. The discovery of these fossil gases opens the door to a better understanding of the origin of water and other life-supporting species on Earth.