From the Outer Solar Nebula to Earth: Linking Protoplanetary Disk Evolution to Terrestrial Planet Formation

Speaker: Dr Elishevah van Kooten (University of Copenhagen)
Series: Department of Earth Sciences Seminars (downtown)

Understanding the formation of Earth and the terrestrial planets requires placing their accretion histories within the broader physicochemical evolution of the protoplanetary disk. In particular, the outer disk plays a critical role in regulating the distribution and delivery of volatiles—such as water and organic compounds—to the initially hot and volatile-poor inner Solar System, directly influencing the habitability of rocky planets. Models of terrestrial planet formation, ranging from classical accretion scenarios to pebble accretion and giant planet migration, all depend on how material was transported and mixed across the water snow line.

Nucleosynthetic isotope evidence indicates that Earth incorporated a significant component of material that originated beyond the snow line, highlighting the need for stronger constraints on the structure and evolution of the outer disk. Carbonaceous chondrites have long provided our principal cosmochemical record of this region, but their limited diversity may not represent the full range of outer Solar System environments. Recently recognized anomalous carbonaceous chondrites, including ungrouped and isotopically unusual meteorites, offer new opportunities to investigate disk dynamics and mass transport processes.

In this seminar, I will review leading models of terrestrial planet formation in light of nucleosynthetic isotope constraints and present new Si, Mg, Fe, and Cr isotope data from both anomalous and grouped carbonaceous chondrites. These data indicate that the outer disk was replenished by a late influx of isotopically distinct material that contributed more than 30% of the mass in the gas giant formation region yet appears to have played little role in the main accretion phase of the terrestrial planets. Instead, Earth's volatile inventory is most consistent with delivery from CI-like planetesimals that formed near an inward-migrating water ice line. Together, these findings reveal a dynamic and evolving outer disk and demonstrate how cosmochemical records can be integrated with astronomical observations to build physically consistent models for the formation of Earth and the terrestrial planets.