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Project Progress

Work continues on reconstructing Earth’s orbital and climate history for the past 100 million years. Possible connections between chaos in the motion of inner planets and asteroid impacts are being investigated with new numerical simulations. Our team made significant progress on coupling orbital-dynamical and viscoelastic modeling of the Galilean satellites this past year. We obtained detailed information on the likely rotational states (so-called Cassini states) of the Galilean moons. This information is now being used to interpret data from the Galileo space mission. We have discovered that simple, commonly adopted viscoelastic models of deformations may lead to rotational instabilities. Combining our simulation results with observations is expected to provide new constraints on the internal structures of the Galilean satellites.

Results of a geochemical study of three early Archaen spherule beds from Barberton, South Africa, were reported in 2003. The three units have anomalous Cr isotope ratios that, together with large Ir anomalies, confirm that they contain substantial components of extraterrestrial material resembling carbonaceous chondrite meteorites. The beds appear to be global ejecta from very large-body impacts that were larger than the Cretaceous-Tertiary event. Since all three of these major events occurred within 20 million years of one another, it appears that the flux of impactors at ca. 3.2 Ga was an order of magnitude greater than today.

Papers from the Rubey Colloquium on Impacts and the Origin, Evolution, and Extinction of Life held at UCLA were published this year.