Estimate of the Influx of Extraterrestrial Material during the Silurian

Abstract

Parkin and Tilles¹ recently described the methods used for measuring the influx of extraterrestrial material to the Earth's surface and discussed critically the significance of the results so far obtained. In particular, they mentioned unpublished work by J. L. Barker, in which the abundances of osmium and iridium in deep sea sediments had been applied to the estimation of the infall rate. This was of interest because, in the course of an extensive study of the distribution of rhenium and osmium in rocks², the abundances of trace elements in a Silurian shale had been applied in a similar way. Although the relevant data required for the calculation have been published previously^3–6 the result has not, and to do so is the intention of this communication.