Seminar Hugh O’Neill

On Earth, the most abundant element in nearly every rock is oxygen, which is unsurprising given that oxygen is the third most abundant element in oursolar 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%. The important point is that 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. In our solar system, O is calculated to condense from the solar nebula in significant amounts from the highest temperatures as oxides in the most refractory components, to the finish, as planetary ices like H2O. This sequence is entirely different from that of any other element in the Periodic Table. 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.