No abstract

Otherwise unrelated geophysical and astrophysical observations can be consistently accounted for by postulating that the earth has been subjected to comet storms. The phenomena include features of the fossil record, impact craters and glass, geomagnetic reversals, and cosmic ray exposure ages ofH-chondrite meteorites. Monte Carlo analyses of both the extinction data and the crater data suggest that these data are periodic.Theoretically, periodicity in impacts on the earth requires that the impacting bodies arrive in large numbers as in a comet storm. A number of causes have been suggested for periodic showers of comets, but presently only the Nemesis hypothesis of a solar companion star is consistent with all the known data. We are searching for this star by measuring the parallax of faint red stars that would have been missed in catalogues of bright and nearby stars. So far, we have rejected about 20% of the 2,691 stars in our list of candidates in the northern hemisphere.