Research Interest:

The solar nebula is the gas and dust cloud from which the planets formed. Several different kinds of primitive meteorites called chondrites were formed by grain agglomeration in the solar nebula and have experienced nearly no alteration since their formation. By studying the compositions of such chondrites we obtain information that can be used to model the solar nebula, i.e., to infer its composition, its pressure, and its temperature history. We separate different components of these chondrites and use neutron activation and electron microprobe analysis to study their compositions. One example is our study of chondrules, millimeter-size spherules formed as molten droplets in the nebula. The origin of chondrules is still poorly understood.

One of our projects combines chemistry, biology and geology; we are investigating the association between the accretion to the Earth of large, kilometer-size objects and massive biological extinctions. The chemical evidence for the accretionary events are large enhancements of noble-metal concentrations in thin sediment layers. Our recent determinations of Ir in a sea-sediment core have allowed us to determine the size of the impacting body that produced the Australasian tektites.

Other research projects we are pursuing include: (1) the characterization of unusual classes of chondritic meteorites, and interpretation of the results in terms of formation in the solar nebula at specific distances from the Sun; (2) the characterization of iron meteorites, and the interpretation of the results in terms of various models including planetary core formation followed by fractional crystallization; and (3) the relationships of the meteorites to known asteroids.