Describe the evidence for continental drift. (12 marks)
Describe the evidence for continental drift. (12 marks)
The study of rocks and fossils formed over millions of years has helped geologists establish a time chart. It is evident that the Earth's surface has changed greatly. There is a noticeable jigsaw like fit between South America and West Africa. Other similar shaped coastlines on different continents can also be noticed. There is evidence that all the continents were joined together as one large super continent, which was named 'Pangaea'. The evidence for Wegener's theory (above) can be collected into 3 groups, they are, biology, geology and climatology.
In India and Antarctica a similar plant fossil was found as well as a reptile, named 'Mesosaurus' which existed only in South Africa and Brazil. This showed that similar vegetation and wild life existed in places that are thousands of miles away from each other now, as it is unlikely the animals could travel distances by sea. This suggests that they were once close together in an area with the right conditions.
The second strand of evidence for continental drift is that rocks of resembling age, type, formation and structure have been found in Southeast Brazil and South Africa as well as the mountains in eastern USA which are similar to that of north west Europe. This suggests that the rocks were formed together in the same place.
The third piece of evidence of continental drift is that coal which could have only been formed in warm, damp conditions, was found beneath the Antarctic ice cap and in Britain, which does not have a warm climate any more. Evidence ...
This is a preview of the whole essay
The second strand of evidence for continental drift is that rocks of resembling age, type, formation and structure have been found in Southeast Brazil and South Africa as well as the mountains in eastern USA which are similar to that of north west Europe. This suggests that the rocks were formed together in the same place.
The third piece of evidence of continental drift is that coal which could have only been formed in warm, damp conditions, was found beneath the Antarctic ice cap and in Britain, which does not have a warm climate any more. Evidence of glaciation had been noted in India and tropical Brazil, looking at a world atlas we can see that Brazil and India are very near the equator. This shows that these places have not always been where they are now.
This evidence shows that some continents and countries could not have been where they are now at present because of the biological, geological and climatological reasons. But there are three more recent pieces of evidence found since Wegener made his theory in 1912.
It was realised that the mountainous range of islands in the Atlantic were volcanic and recent. This showed that magma was rising from between cracks in the Earths surface: the plate boundary, and forming new volcanoes. The sea floor is spreading, the evidence for this is that the newest rocks have been found near the North Atlantic Ridge, and the oldest rock near North America. Therefore shows that the Atlantic is spreading apart, therefore the Eurasian plate and North American are moving further and further apart.
Another piece of recent evidence is the magnetic fields that have been studied, it shows that periodically the magnetic poles have been alternating many times, and is identical on both sides of the ridge e.g. the Mid-Atlantic Ridge.
Explain the processes responsible for continental drift (8 marks)
The Earth is made of three layers, the core (in the centre), the mantle (in the middle), and the crust (continental and oceanic plates). The core is extremely hot, this causes mantle to become molten and to rise in convectional currents, and once it is cool it sinks. All the time these convectional currents are moving the plates.
These plates, oceanic and continental, sometimes are constructive (moving apart), are colliding (two continental plates), or destructive (two different plates moving together) or passive (sliding past each other) due to the convection currents. Different landforms can be found at these places e.g. (submarine) volcanoes, fold mountains, rift valleys, transform faults, island arcs and batholiths.
Constructive margins are when plates move apart because the convectional currents are in opposite directions. As the earth never has 'gaps', magma flowing under the crust rises and fills the space in; this is why we have sea floor spreading. But because the Earth is neither shrinking nor getting larger, there is not enough space for the new crust and the old, so some of the older oceanic crust must be destroyed in another place on Earth.
This destroying of oceanic crust happens at destructive plate margins, or subduction zones. This is when an oceanic plate and continental plate moves towards each other. Oceanic crust is heavier therefore it will sink beneath the continental crust and be destroyed forming a deep-sea trench as it returns back into molten magma.
In other places in the world e.g. the Himalayas, where two continental plates are converging, neither will sink like at a destructive margin but it will form Fold Mountains. Mount Everest has risen since it was last climbed. Two plates are passive when they are sliding past each other either in the same direction at different speeds or in opposite directions, this is all due to convectional currents beneath the crust in the mantle.
