Professor Napier and his colleague Victor Clube, formerly dean of the Astrophysics Department at Oxford University, go so far as to describe the 'unique complex of debris' within the Taurid stream as 'the greatest collision hazard facing the earth at the present time.' Coordination of their findings with those of Allen West, Jim Kennett, and Richard Firestone, as led both teams--the geophysicists and the astronomers--to conclude that it was very likely objects from the then much younger Taurid meteor stream that hit the earth around 12,800 years ago and caused the onset of the Younger Dryas. These objects, orders of magnitude larger than the one that exploded over Tunguska, contained extraterrestrial platinum, and what the evidence from the Greenland ice cores seems to indicate is an epoch of 21 years in which the earth was hit , with the bombardments increasing annually in intensity until the fourteenth year, when they peaked and then began to decline before ceasing in the twenty-first year.