The geochemistry of silicon containing molecules participating in the dynamic physical and chemical processes operative in the upper layers of the earth, the atmosphere, hydrosphere and lithosphere, has been studied using the radionuclide Si 32 as a tracer. In this paper, first of a series, the results of measurements of its concentration in wet precipitations at several stations in India covering the latitude belt 10-32° N are described. The measurements are discussed in relation to the observations of fallout of the short-lived cosmic-ray-produced isotope, Be 7. The observed fallout pattern of Si 32 is discussed in relation to the large-scale atmospheric processes operative in its eventual removal from the atmosphere. The discussion of the analyses leads to reasonable estimates of the rate of production of Si 32 in the atmosphere. This information is of significance for the interpretation of observed activities of Si 32 in the hydrosphere.