Reversals of the Earth's magnetic field and climatic changes

Abstract

IT has been suggested that evolution may be influenced by reversals of the Earth's magnetic field^1–3. It was observed that there were correlations between discontinuities in microfossil assemblages (or evolutionary discontinuities) and reversals of the Earth's magnetic field in deep sea sediment cores^4–6. This observation was put on a firm base when Hays⁷ showed statistically that reversals directly or indirectly exert a selective influence on radiolaria. The explanation offered by Uffen^1,2 and Simpson³ for the connection between evolution and reversals was that during reversals of the Earth's magnetic field, the intensity of the field would be reduced to a very low value, allowing organisms at the surface of the Earth to be bombarded by increased cosmic radiation normally shielded by the field. This increased radiation should then cause an enhanced mutation rate and hence produce an evolutionary discontinuity. It was, however, shown later that the estimated increase in the mutation rate would be small and unlikely to cause evolutionary discontinuities^8–10.