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I am a geochemist and I work on a variety of different systems. My interests range from mantle sources and present day volcanic systems to the formation of the Earth and the early Solar System. My main scientific focus concerns investigating the formation of Earth and the sources and processes of the early solar system. I achieve this by using and developing new isotopic techniques to examine a variety of different rocks and meteorites.

To find out more about my research please see a full list of my publications here and my google scholar page here. I describe some of the areas in which I am interested below.

Isotope anomales in bulk meteorites

Since the solar system formed, 4.567 billion years ago, it has undergone substantial processing and elemental isotopic compositions have been significantly, but not fully, homogenised. By examining the small variations in the isotopic compositions of elements in meteorites we are able to investigate the astrophysical birth environment of the solar system.

During my PhD, I worked on the mass-independent compositions of Ni isotopes in meteorites. I found that the variation in the isotopic compositions of Ni in meteorites showed evidence for a variable contribution from the Si/S zone of a type II supernova. Significantly, this is a much more likely source than the type Ia supernova source which had been favoured by previous workers.

You can read more about this work in my papers, particularly Steele et al 2011 and Steele et al 2012.

Isotope anomalies in hibonite grains and meteorite inclusions

The Ti isotope variations observed in hibonites represent some of the largest isotope anomalies observed in the solar system. Titanium isotope compositions have previously been reported for a wide variety of different early solar system materials, including calcium, aluminum rich inclusions (CAIs) and CM hibonite grains, some of the earliest materials to form in the solar system, and bulk meteorites which formed later. These data have the potential to allow mixing of material to be traced between many different regions of the early solar system. We have used independent component analysis to examine the mixing end-members required to produce the compositions observed in the different data sets. The independent component analysis yields results identical to a linear regression for the bulk meteorites. The components identified for hibonite suggest that most of the grains are consistent with binary mixing from one of three highly anomalous nucleosynthetic sources. Comparison of these end-members show that the sources which dominate the variation of compositions in the meteorite parent body forming regions was not present in the region in which the hibonites formed. This suggests that the source which dominates variation in Ti isotope anomalies between the bulk meteorites was not present when the hibonite grains were forming. One explanation is that the bulk meteorite source may not be a primary nucleosynthetic source but was created by mixing two or more of the hibonite sources. Alternatively, the hibonite sources may have been diluted during subsequent nebula processing and are not a dominant solar system signatures.

Read more about this work in Steele and Boehnke 2015

Earth's accretion

In some of my current work, I am looking at the final stages of Earth's accretion. Working with Maria Schonbachler (ETH) and Carsten Munker (Cologne), I am measuring Cr isotope compositions in archean rocks, which are some of the old rock preserved on Earth. Using these data we aim to investigate the final stages of Earth's accretion.

© Bob Steele 2019