Richard B. Firestone, Lawrence Berkeley National Laboratory
Allen West, GeoScience Consulting
Theodore E. Bunch, Northern Arizona University and NASA Ames Research Center (retired)
James H. Wittke, Northern Arizona University

We have found evidence of an extraterrestrial impact event in sediments dated to 13,000 ca yr. BP at the Gainey, Murray Springs, Blackwater, and Topper Clovis sites and four additional sites in Manitoba. High concentrations of magnetic particles and spherules were extracted with a magnet at each of these sites but not from the adjacent sediment layers. Carbon rich impactites, charcoal, and low-density, nonmagnetic spherules were also found in association with the magnetic particles but nowhere else. Survey of these sediments with a radiation meter indicated a sharp increase in radioactivity near the 13,000 ca yr. BP layer at all sites and a second increase at the Topper site in a layer estimated to be 40,000 ca yr. BP. Samples from the younger layer were analyzed by Neutron Activation Analysis and found to be substantially enriched in U, and Th, naturally radioactive elements, explaining the increased radioactivity in this layer. These results are consistent with the explosion of a near-earth supernova that would have irradiated the earth 40,000 years ago with a gamma-ray burst and again 13,000 years ago with the impact of a cloud of supernova ejecta. Supporting evidence from the cosmogenic isotope record of the past 40,000 years, analysis of lunar and Martian sediment data, and elemental and isotopic analysis of the impact layers and artifacts will be presented. The implications to the extinctions of megafauna and the impact on humans during that time will be discussed.

Richard B. Firestone
Dr. Richard B. Firestone graduated from the University of Michigan and received his Ph.D. from Michigan State University in 1974. He is a nuclear scientist at the Lawrence Berkeley National Laboratory and author of 5 books, including the Table of Isotopes, and 200 papers on subjects ranging from nuclear physics, to archaeology, analytical chemistry, and denitrification. With colleagues at the Budapest Reactor he has developed the technique of Prompt Gamma-ray Activation Analysis (PGAA), a nondestructive method for the simultaneous quantitative analysis of all elements from hydrogen to uranium in a variety of materials. He is interested in studying near-earth cosmic catastrophes, the signatures they leave on the solar system, and their impact on life and climate on our planet.