TECTONICS - Theories of plate motion
- Created by: aliceoliviaaa
- Created on: 26-04-18 10:34
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- Theories of plate motion
- Plates move at a speed of 2-5cm per year.
- There are 7 large major plates - (African, Pacific etc).
- and smaller minor plates (Nazca, Philippine Sea).
- And dozens of small microplates.
- All the plates fit together to form the lithosphere. each plate is 100km thick approx. the lower part is upper mantle, and the upper part is crust (oceanic or continental).
- 1) Alfred Wegener's continental drift hypothesis (1912)
- now separate continents were once joined (PANGAEA, a super-continent).
- 2) Arthur Holmes internal radioactive heath theory (1930)
- internal radioactive heat was the driving force of mantle convection that could move tectonic plates.
- 3) discovery of aesthenosphere - a weak deformable layer beneath the rigid lithosphere - the lithosphere is sitting on it.
- 4) discovery of magnetic stripes in the oceanic crust of the sea bed: Paleo-magnetism. (1960)
- magma on the oceanic crustal sea bed which 'locks in' the earth's magnetic polarity at the time it cools. Scientists can use this to determine historic periods of high tectonic activity. (create a geo-timeline)
- This proves that new oceanic crust is being produced at sea-floor spreading. (Divergent)
- magma on the oceanic crustal sea bed which 'locks in' the earth's magnetic polarity at the time it cools. Scientists can use this to determine historic periods of high tectonic activity. (create a geo-timeline)
- 5) Tuzo Wilson recognised transforming faults (1965)
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