Speaker
William McDonough
(University of Maryland)
Description
Compositional models of the core and lower mantle will be reviewed and assessed. Assumptions in the models along with constraints and uncertainties of the Earth’s interior will be presented. Although a compositional model for the lower mantle that matches that of the upper mantle for major elements is most compatible with observations and constraints, uncertainties are such that competing compositional models are tenable.
Based on chondritic models, more than 90% of the mass for the Earth is composed of Fe, O, Mg and Si and the addition of Ni, Ca, Al and S accounts for more than 98% by mass the composition of the Earth. Geoneutrino studies are placing global scale limits on the amount of Th and U in the Earth, which in turn will constrain models for the composition of the bulk silicate Earth, the mode proportion of the Ca-bearing phase in the deep mantle, and the thermal evolution of the planet.
Compositional models for the core are constrained by limited variation in chondrites for key siderophile element ratios (e.g., Fe/Ni, Ni/Co, and Ni/Ir). However, the amount and relative proportions of light element(s) in the core remain poorly constrained, with tradeoffs and modeling uncertainties in core temperatures and compositional space that allow for a range of model solutions. Constraints on the absolute and relative abundances of moderately volatile and volatile elements in the bulk Earth are consistent with only ~2% by mass of sulfur and a negligible role for H, C or N in the core. There is no evidence that heat producing elements (HPE: K, Th and U) are in the core at any significant level. Important targets for neutrino oscillation studies include establishing Z/A constraints for the outer core and Z/A contrast between inner and outer core.
Author
William McDonough
(University of Maryland)
