EPSS Colloquium fall-2017

A paradigm has arisen over the relationship of late accretion and the delivery of water and other volatile compounds and element. Late accretion, which can be defined as the addition of materials after metal-silicate equilibrium, is effectively tracked using the highly siderophile elements (HSE). Thus, there should be a link between the HSE and volatile elements. Alternatively, the distribution of volatile elements and the HSE in the Earth and Moon were set by a range of fundamental processes, including planetary accretion processes and the feedstocks that formed the proto-Earth and Moon, as well as late accretion. The timing of these processes on planetary bodies likely varied in response to mechanisms of accretion, availability and nature of feedstock materials, and cessation of metal-silicate equilibrium. Arguably, the most complex locations to address these issues in the inner Solar System are the Earth and Moon. The likely origin of these bodies, during a late-stage catastrophic ‘Giant Impact’, led to significant volatile loss from the Moon, redistribution of the HSE and volatile elements between the colliding bodies, planetary-scale magma oceans, prolonged late accretion and, in the case of Earth, silicate remixing (aka Plate Tectonics). Given this diverse array of processes, how is it possible to go about deriving likely distributions of the HSE and volatile elements in Proto-Earth or Moon materials? In this talk, I will review evidence from the distribution of volatiles and HSE in chondrites and achondrites – the likeliest examples of possible feedstock materials to the proto-Earth and Moon and possible scenarios of feedstock composition.