LOW SEA LEVELS, DROUGHTS AND MAMMALIAN EXTINCTIONS

DRASTIC environmental changes and mammalian extinctions have been reported to coincide with low ocean levels. These low levels were, therefore, interpreted as being caused by major climatic coolings with glacial eustatic regressions, although no continental glaciations, or cooling of Pleistocene-type, has been recorded outside Antarctica earlier than ∼ 3 Myr ago. We give here a simple geophysical solution to this problem, which is that any regression (glacial eustatic, tectono eustatic or geoidal eustatic) will also affect the ground water table under the continents by geoid changes and hence lead to drastic environmental and faunal changes, including extinctions. Instead of extinction by temperature decrease, the chain reaction 'regression-drought-extinction' is proposed. Continental geoid fluctuations affecting the ground water table are not only essential for correct interpretation of the pre-Pleistocene climate but also for understanding and modelling of the Pleistocene climate, because the dryness in equatorial and low-latitude regions during ice ages may be interpreted rather as an effect of the lowered geoid and ground water table than of the temperature decrease, although, in this case, the latter is of a significant order of magnitude. © 1978 Nature Publishing Group.