NEW ESTIMATES OF THE SIZES AND IMPACT VELOCITIES OF ARCHEAN IMPACTORS

We have constructed a numerical model of spherule formation in an impact produced vapor plume. This model tracks the expansion of the vapor plume using a one-dimensional Lagrangian hydrocode coupled with the ANEOS equation of state for silica. As the vapor plume expands and cools spherules begin to condense from the vapor. We model the condensation process by including the equations for nucleation and growth as described by homogeneous nucleation theory. A major result of this model is a new understanding of the dependence of spherule size on both impactor size and impact velocity. We make a comparison between the models results and the observations of spherule sizes in the Archean spherule layers. This comparison leads to an estimate of the impactor sizes and impact velocities responsible for these spherule layers.