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11 Cards in this Set

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What is continental drift?
the theory that the continental landmasses have changed position over time.
What is the geological evidence for continental drift?
The way in which continents (e.g. South America and Africa)appear to fit together. Especially when you look at the continental shelf rather than the present coastline.

Rock types and geological structures are similar on both sides of the Atlantic. E.g. The Appalachian Mountains (N.America) and the Caledonian Mountains (Scotland) both have the same sequence of igneous and sedimentary rocks.
What biological evidence for continental drift is there?
Some fossils (e.g. Mesosaurus) are found in both SW.Africa and Brasil - landmasses wre joined and creatures lived in the whole combined area

Fossils of a fern (Glossopteris) are found widely across the southern continents.

Fossils of Triassic period reptiles have been found in areas which are now far apart. E.g. Cynagnathus in S.America and Africa.
What is the Climatological evidence for continental drift?
The coal and oil reserves found in Antatrtica suggests that this area was once in a different climatic zone.

Glacial striations in Brazil and W.Africa
Gklacial deposits in India, South Americal and the Vaal Valley in South Africa.

These landmarks suggest that the areas once had very simelar climatic conditions even though they are now far apart and in very different climatic zones.
According to Wegener, what was Earth like 300 million years ago?
All the continents were joined together 300 million years ago as a single supercontinent caleed Pangaea
According to Wegener, what was happening to the tectonic structure of Earth 200 million years ago?
The continents drifted apart. This formed:
-a northern hemishere aseemblage known a Laurasia comprising of Eurasia and North America.

- A Southern hemisphere group called Gondwanaland consisting of Africa, Australasia, India, South America and Antartica
Why was Wegener's theory not widely accepted?
-He was not a meteorologist
- He could not explain how or why the plates moved (He did have some suggestions though - centrifugal force and the gravitational force of the moon).
What is the plate tectonic theroy?
The Earth's crust is divided into several major and a number of smaller plates of relatively rigid crust material. The plates move in realtion to each other, riding on the weak, soft and partially molten rocks beneath.
What evidence is there for sea-floor spreading and plate tectonic movement?
The basaltic rocks near the mid atlantic ridge are much newer than those found near the continental shelves. This is evidence that rocks were formed at the ridge and have then moved apart being replaced by new rocks which form at the ridge.
how does the palaeomagnetism of basalt rocks suggest that rock has been formed at a ridge and then moved apart?
There is a parallel pattern of magnetism in the rocks. this develops because, as the magma cools and solidifies, the metallic elements within it are magnetised in the direction of the Earth's magnetic field. There have been many reversals of the earth's magnetic field over time - The pattern of magnetism found in the rocks relates to the alternating pattern of of northely and southerly magnetism of the earth's magnetic field.
What is the mechanism for the movement of the tectonic plates?
Convection currents beneath the earth's surface.