Margot Debruycker’s PhD

The origin of sulfur and other volatile elements on Earth

Understanding the origin of terrestrial planets is a fundamental aspect of planetary sciences. The origin and the timing delivery of Earth’s volatiles remain debated. A substantial fraction of Earth’s volatiles may have been brought during the main stage of planetary growth. They would have been carried by the parent bodies of the Earth and would have never escaped the planet. Alternatively, volatiles could have been delivered late during planet formation to a dry proto-Earth. The provenance of Earth’s volatiles is another open question. Some suggest that volatiles were provided by parent bodies from the inner solar system. Other invoke volatile-rich material from the outer solar system: asteroids from the outer solar system could have been thrown towards the inner disk and contributed to Earth’s accretion.

Sulfur is a volatile element, with a condensation temperature similar to that of selenium and zinc. Constraining the origin of sulfur on Earth may help disambiguating scenarios of volatile origins. For instance, based on its concentration in the mantle, the budget of terrestrial sulfur has been tied to a late-veneer of the volatile-rich CM chondrites. However, the sulfur isotope composition of CM chondrites shows mass-independent isotopic anomalies that are inconsistent with Earth’s composition. The anomalies challenge scenarios involving CM chondrites as a major