The continental drift theory and it’s effects on evolution Essay
The continental drift theory and it’s effects on evolution
Continental Drift is the principle that the continent landmasses have not remained in fixed positions, but have moved around the earth’s surface apparently independently. It is important in evolution because of the effects it has had on evolution and taxonomic diversity, brought about by the collision and moving apart of landmasses. The drifting apart of land masses brings about vicariance, where organisms are split up by the development of barriers, isolating descendent populations which then evolve to form new taxa.
Pre-continental drift theory, it was believed that species originated in a particular area, and spread out from there to colonise new habitats. However, it was noted that on a worldwide scale many taxa had obvious close relatives in regions that were geographically widely separated with natural barriers i.e.; oceans, deserts or mountain chains. Therefore, continental drift theory was able to explain many previously unanswered questions. An example of this is Nothofagus. Nothofagus is restricted to the southern hemisphere, and is widely dispersed geographically. Although there are significant morphological differences between the species of Nothofagus, they all have seeds seemingly poorly adapted for long range dispersal, and are also intolerant of immersion in salt water.
Continental drift reconstruction recognises that the southern continents were once united as a single massive continental land mass called Gondwanaland, and this lends weight to the vicariance hypothesis. Further evidence comes from fossil record, where remains of pollen grains of Northofagus have been found in regions outside the present range of any living species, namely Antarctica, Western Australia and Patagonia. This also confirms that the climate of Antarctica in Cretaceous times was very different from today. Landmasses undergo major changes of climate as they move across different latitudes.
This affects evolutionary processes in that greater species diversity accumulates under tropical climatic conditions. Another effect that continental drift has on evolutionary processes is that of continental collision. Marine fauna, deep water and coastal are likely to suffer destruction of habitat and hence extinction. Also, when these land masses collide, species that have become adapted to identical niches, disperse onto the other continent and from there spread out. At first this will increase diversity, but then competition and extinction are likely to decrease the number of species.
Collision of continents are also likely to form mountain belts. This is the result of the landmasses being forced together and the outer parts of the land being forced upwards. This in itself would affect evolutionary processes, in that they will provide new and diverse habitats, but also serve as natural barriers, which could encourage vicariance.
The ocean also shows evidence of continental movement. It has been for example, on examination of Ordovician rocks in Scotland, the fossils were shown to have greater similarity to fossils more geographically dispersed than to adjacent fossil faunas of the English Lake District and Wales. The accepted suggestion for the anomalous distribution of Ordovician Faunas, is that an ocean, known as the Iapetus Ocean, separated the landmasses which today are most of North American and Europe.
The Iapetus Ocean eventually closed, and with the opening up of the Atlantic Ocean, Scotland, which was formally part of North America, remained attached to Europe. As Iapetus started to close a genus of floating graptolites called Rhabdinopora, which can swim enormous distances, traversed the ocean to colonise the other side. As the width of the ocean decreased, Bethnic invertebrates such as trilobites and brachiopods also crossed. This was achieved by their swimming larval forms, which allow dispersal.
In conclusion, it appears continental drift has had a far-reaching affect on the patterns of evolution among organisms. Marine species have had obvious effects by opening and closing of oceans, such as Iapetus. Changes in climate as the continents moved have created opportunity for species diversity, and continental collision, new habitats and natural barriers, which encouraged vicariance and allopatric speciation.