theory of plate tectonics
In 1912 Alfred Wegener, a german geophysicist and meteorologist published his theory of 'Continental Drift' in order to explain our present geological positioning of earth's continents. This concept describes how the continents have moved relative to one another and the ocean floor, rather than being permanently locked in place.
Wegener theorized that originally all continental land was joined as a single supercontinent called Pangea (meaning 'all earth') which split into 2 parts 140 million years ago; Laurasia in the north which included North America, Greenland and Eurasia and Gondwanaland in the south which was made up of South America, Africa, India, Australia and Antarctica. It was believed these two subcontinents were separated by the Tethys Sea, with oceans making up the rest of the world.
Wegener theorized that originally all continental land was joined as a single supercontinent called Pangea (meaning 'all earth') which split into 2 parts 140 million years ago; Laurasia in the north which included North America, Greenland and Eurasia and Gondwanaland in the south which was made up of South America, Africa, India, Australia and Antarctica. It was believed these two subcontinents were separated by the Tethys Sea, with oceans making up the rest of the world.
*Top Tip*
Click below for an animation showing the splitting up of Pangea
Click below for an animation showing the splitting up of Pangea
Wegener's theory was based on various pieces of scientific evidence:
1. The jigsaw fit of the continents. When pieced together they fit near perfectly with very little overlap.
2. Faunal/Biological- fossils of the Mesosauras were found in both South Africa and South America
where it is unlikely this freshwater reptile could have migrated thousands of miles across the Atlantic in salt water, or evolved identically on separate continents. Living species of earthworms belonging to the same family were found in North America, South America and Africa which would not exist if the continents were not connected at one time.
3. Geological- rocks of both similar age and type were found in south east Brazil, South Africa, the Appalachian Mountains in eastern USA and mountains of North West Europe. These locations are at different latitudes and so unless these locations were previously been joined, this is unlikely. Rock sequences in northern Scotland closely agree with those in eastern Canada, indicating that they too were laid down under the same conditions in one location.
4. Climatologic- Coal was found in Antarctica yet this is unlikely to have formed at its current latitude as it requires warm, wet conditions and dense vegetation. In addition, there is evidence of glaciation in tropical Brazil.
Wegener's ideas did not achieve immediate acceptance because people argued they could not see or feel any of the suggested tectonic movements. His theory sparked controversy as a result of its one fatal flaw; there was a lack of evidence for a propelling mechanism to drive this continental drift.