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Mitchell Earth Sciences, B67
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Isotopes are useful probes of planet formation and evolution for at least two reasons.
Some exhibit nucleosynthetic anomalies providing clues to their original location. Others undergo
decay, providing age constraints. In this talk, I'll discuss two applications of these
ideas. The fact that the silicate Earth records different fractions of "carbonaceous" material in
different elements implies that it experienced a change in the material it was accreting over time.
The first ~95% was "non-carbonaceous", while the last ~5% was "carbonaceous" and volatile-rich.
Reconciling these constraints with existing planetary accretion scenarios is not easy. In the second
part, I'll discuss the idea that the pile-up of lunar ages around 4.35 Gyr is not the signature of
magma ocean crystallization but is instead related to a tidal heating event. This story allows the
Moon to be older (~4.45 Gyr or so), which is easier to reconcile with dynamical models.
Francis Nimmo's interests are the interiors and evolution of solid
solar system bodies. He received his BA in 1993 and PhD in 1996, both from
Cambridge University. He joined the faculty at UC Santa Cruz in 2005 and received
the Macelwane medal and Urey prize in 2007. He served on the GRAIL, Cassini, New
Horizons and InSight missions and is a member of four teams on Europa Clipper.
He was elected to the National Academy of Sciences in 2020 and the Royal Society
in 2024.