Narrow Results

Cycles of glaciation with an average period of ~100 kyr are mediated by impacts of cometary bolides. Ice-age conditions are dry and dusty with low rates of precipitation. Comets in the mass range 10¹⁵–10¹⁶ g impacting the oceans could release enough water vapour into the atmosphere to enhance a depleted greenhouse effect. The energy deposited in the oceans would also warm the surface layers, thus starting up an evaporation-precipitation cycle which ushers in warmer interglacial interludes. The latter have neutral stability and are necessarily short-lived, eventually drifting back to glacial conditions on timescales of ~10 kyr.