The Ice Age
Does Crustal Overturn Drive Evolution
Crustal overturn, or smaller crustal mass movements may have been an important driving force for the evolution of life, just as much as commetary impacts.
Crustal overturn triggered by the collapse of a major ice mountain would normally rotate the crust around an equatorial axis - turning round two points on the equator on opposite sides of the earth. These equatorial regions at these two points may suffer little climate change through this event and intothe next epoch. These will remain as centres of biological diversity fromwhich species will migrate out. The further away from this axis of rotation, the bigger the changes in climate that are possible after an overturn. At the most extreme tropics become polar and poles become tropical, examples of which are clearly shown by the stratigraphy of the rocks laid down by successiveevents.
In regions where the changes in climate are not too drastic, the animals and plants may be poorly adapted to the climate, but unles they are overwhelmed by better adapted migrants, they may survive and evolve to suit the changed climate. However the crustal overturn is likely to initiate a mass extinction event.
This is exactly what we find at the end of the last ice age. The diverse animal life of Siberia almost wiped out, along with the plants that supported them. The south of South America also left almost devoid of much of its animal life by a sudden cooling of the climate, but the biological diversity of theAfrican tropics and Central America remain almost intact in regions where the climate remained much the same.
The Sahara turned from woodland and savannah into desert as the moisture that was brought by moist westerly winds during the ice ages drained away, or evaporated. It has little plant or animal life adapted to these desert conditions.
The ancient deserts of Australia with their biological diversity remain intact, but they are spreading into the regions occupied by tropical forest. The wild life of Southern Australia is suprisingly well adapted to a colder climate - wallabies can fend for themselves in the cold temperate climate of the Yorkshire moors in the UK, and many eucalyptus trees grow wellin colder, wetter conditions.
The great barrier reef of Western Australia only started to grow at theend of the last ice age - before that the region was too far south and toocold for coral reefs - but the corals survived the ice age in all their diversity in warm tropical seas.
This information is copyright Peter Thomson 2001-2004