The Solar System was evidently formed 4567 million years ago in much the same way as stars with planets are forming today. Following 'in-fall' in a molecular cloud, a disk of gas and dust surrounded the infant Sun.  Material in the disk aggregated into small bodies (planetesimals) that in turn coalesced to make our planets.  Meteorites are interpreted  as fragments of planetesimals that failed to become a large planet, and thus they preserve evidence for the nature of Solar System material at a very early, pre-planetary stage in the disk.  Recent research has refined the timing of meteorite formation with truly remarkable precision, and this new knowledge has forced a change in our understanding of events during the first five million years.  In particular, so-called primitive meteorites, whose chemistry is remarkably similar to that of the Sun, were always presumed to be samples of the first-formed planetesimals; they now turn out to be bits of the last-formed planetesimals.  The earliest planetesimals were, it seems, so radioactive that they melted rapidly; iron meteorites are interpreted as surviving bits of their once-molten cores.

Biography -

Studied mineralogy and petrology (PhD 1972) at the University of Cambridge, and taught at TCD in the Department of Geology since 1971.  Interests span the whole range of 'hard rock' geology, and since 1992 they have focused on the geology of asteroids, and the formation of planets.