Evolutionary Processes and Reversals of the Earth's Magnetic Field

Abstract

IT has been suggested that there is a connexion between reversals of the Earth's magnetic field and evolutionary processes1–3. This topic has excited much interest since the discovery of an apparent correlation between levels of field reversal and microfaunal discontinuities in deep sea sediment cores4. The Earth's magnetic field is known to have reversed its polarity at least nine times during the past 4 × 106 yr5,6 and at frequent intervals before that except during the Permian7. Briefly, the ideas of Uffen1,2 and Simpson3 are that during the process of a reversal there is a period of reduced or zero intensity of the dipole field during which there should be a great increase of cosmic radiation at the Earth, which is no longer shielded by its magnetic field. This enhanced radiation will produce a higher mutation rate, which will result in some kind of evolutionary discontinuity. There is good evidence that during the process of reversal, the Earth's dipole field is reduced in strength, probably passing through zdro4,8. The other assumptions are less acceptable.