Signs of Nemesis: Meteors, Magnetism
Thomsen, Dietrick E., Science News
Signs of Nemesis: Meteors, magnetism
A well-known hypothesis blames impactsof cometes--triggered by Nemesis, the alleged companion star to the sun-- for mass extinctions of biological species that appear to have occurred periodically in the history of the earth. In the attempt to show that such cometary impacts did happen, proponents of this hypothesis are marshaling evidence from other events that might have been the result of an enlarged presence of comets in the inner solar system at the appropriate times.
The latest piece of such evidenceconcerns the ages of the so-called H class of chondritic meteorites. It was presented in San Francisco, at the recent meeting of the American Physical Society and the American Association of Physics Teachers, by Richard A. Muller of the Lawrence Berkeley (Calif.) Laboratory (LBL).
The H class are the chondrites with ahigh iron content. The work by Saul Perlmutter of LBL and Muller indicates a periodicity in the ages of the H chondrites that coincides with the times of mass extinction.
The meteorites are presumed to bepieces broken off asteroids, by the impact of another asteroid or perhaps a comet. It turns out that large numbers of such meteorite liberations bunched up at or near the times of the mass extinctions. The cause of such wholesale meteorite formation, the researchers suggest, could be showers of comets moving through the asteroid belt--the same comets that, hitting the earth, triggered the climate changes necessary for mass extinctions.
The climate changes that would havebeen caused by the comet showers could also have brought about reversals of the earth's magnetic field (SN: 3/29/86, p.197), according to an analysis published by Muller and Donald E. …