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Discuss the evidence for plate tectonic theory.

This question is a 10 marker and comes at the end of the 25 mark section on Plate Tectonics. 

When answering a Discuss question it is important to remeber that it is in essence a mini essay, however, it is shorter, approximately 2-3 pages. This may seem daunting for a 10 marker but hopefully over time you will realise that it is actually a challenge to keep the answer short.

This introuction requires the student to state that this theory has been worked on as early as 1620 by Francis Bacon, and that it is constantly evolving and that new evidence is constantly being found. This furthers eplanations of various tectonic and volcanic processess. 

Main evidence:

1912 Alfred Wegener. Super continet (called Pangea). Evidence includes

continental fit (e.g. South America and Africa-This is particuarly the case if continental shelfs (often below the suface of the sea) are matched together)

Geological evidence-same rock types, same formations found only in Africa and SA. 

Similar glacial depostis in Antarctica, SA, and India. 

Mountain types and compostion same in eastern USA and NW Europe.

Climatological evidence-Antarctica, N America, Svarlbard, UK all contain coal depostis of similar age formed in tropical conditions, therefore continets must have drifted apart since the carboniferous period. 

Biological evidence-same fossils on eithe side of Atlantic. e.g. Mesosaurus only in southern Africa and in SA. More specifically found in sediments from permian age, 280 million years ago. 

plant remains in India and Antarctica identical. Obviously different climates now, so must have once been joined and sharing same climate.

Seperate evidence found from paleomagnetism.

This expands on Wegener's theory's by explaining how continents could move over a solid earth. 

1948 survey of Atlantic ocean floor revealed Mid Atlantic Ridge (MAR). 1000 km wide, heights of up to 2.5 km. volcanic rocks. Similar range found in pacific later, extending over 5000 km. 

Later surveys showed paleomagnetic stiping to either side of MAR. 

Volcanic rocks/lava, is rich in iron. This iron becomes aligned with magnetic field of earth. Every 400,000 years polarity of earth changes. This is mirrored by bands of rock in normal and reverse polarity orrientation being found either side of the MAR going spreading outwards. 

Lots of fieldwork on Iceland (sits and is being created currently by the MAR) gives us further evidence. 

Subduction of crust in other areas shows us that tectonic plates are moving. 

So far the evidence has just been listed. However, it is necessary to discuss this. The stundent needs to discuss what conutations this evidence has on us. For example, it allows us to trace plate boundaris and so where there are potentially hazardous tectonic areas-earthquakes, volcanoes, tsunamis. etc. 

In essence more than just basic fact listing is needed. Some flare is required as long as the essay remains logical and concise. 

Philip B. A Level Geography tutor, A Level German tutor, GCSE Geograp...

1 year ago

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