OXYGEN IN EARTH-LIKE PLANETS
Seminars
Semester 1
Prof. Hugh O’Neill is an earth scientist whose career has focused on experimental petrology and geochemistry. His work has aimed at advancing our understanding of how rocky planets form, using experimental and theoretical studies of the thermodynamic properties of minerals and melts to solve large-scale geological problems. He has contributed to the understanding of several key questions relating to our planet, including: the chemical composition of Earth and how it differs from other planets; the origin of the Moon; the geochemical evolution of the Earth’s mantle; and the origin of basalts. His current research interests include the composition of the Earth compared to other rocky planetary bodies, the solubilities of volatile species in magmas, diffusion and other transport properties of minerals, the trace-element geochemistry of basalts, and X-ray Absorption Spectroscopy of geomaterials. Hugh is based at the School of Earth, Atmosphere and Environment at Monash University in Melbourne, Australia, and also has a part-time position at the Guangzhou Institute of Geochemistry in China. As well as being a Fellow of the Royal Society and of the Australian Academy of Sciences, he is a Fellow of the American Geophysical Union, the Mineralogical Society of America and the Geochemical Society.
The most abundant element in nearly every rock is oxygen, which is unsurprising given that oxygen is the third most abundant element in the solar system, after H and He. For example, the Bulk Silicate Earth composition of Palme and O’Neill (2014) contains 44.3 wt% oxygen, which is 58.4 % by atomic fraction. The oxygen contents of the most common rocks at the solid Earth’s surface, mid-ocean ridge basalts, are very similar at 44.1(4) wt%. However, small differences in the O contents among rocky planets are expected to translate to large changes in just about every property that characterize such planets, from core formation to the development of gaseous atmospheres. Importantly, the amount of O in the composition of a rocky planet is not well constrained by cosmochemical processes. Uniquely among the elements, O is calculated to condense from the solar nebula in significant amounts from the start, as oxides in the most refractory components, to the finish, as planetary ices like H2O. In this talk, the factors affecting O abundances in the primitive solar system materials thought to make up rocky planets will be reviewed, and then the O abundances in the Bulk Silicate Earth will be assessed from the viewpoint of these factors.