#wegener's theory

[biology-geology-beaches-india]

TSRNOSS, p 769.

[a2geographyprocrastination]

1. Plate Movement - Sea floor spreading and Paeleomagnetism

Sea floor spreading was discovered when the mid atlantic ridge was discovered and studied.

Evidence for this was the alternating polarity of rocks in the earth's crust either side of the mid atlantic ridge.

Iron particles in the lava that erupts from an ocean ridge are aligned with the Earth's magnetic field. when the lava solidifies, these iron particles create a permanent record of the earth's polarity at the moment that piece of crust was created. This is called Palaeomagnetism. since the Earth's polarity reverses approximately every 400,000 years, a series of magnetic stripes.

These "stripes" are mirrored of either side of the ocean ridge, and therefore suggest that the ocean crust is spreading away from this boundary as new crust is being created.

Since new crust is being created and yet the Earth is not getting bigger, crust must also be being destroyed it accomodate for the new crust created at the ocean ridges. this destruction of the earth's crust occurs at ocean trenches, where one plate is being pulled under another. this is called Subduction.

[a2geographyprocrastination]

1. Plate Movement - Evidence for Wegener's Theory

Geological evidence

The visible fit of South America and Africa - see picture of Pangaea

Matching glacial deposits in South America, Antarctica and India which must have been formed before the continents moved apart.

Similar orientation of striations on rocks in Brazil and west Africa.

Rock sequences in northern Scotland similar to those in eastern Canada, suggesting that they were laid down in the same conditions and location.

Biological evidence

Similar fossils of shellfish found in India and in Australia

fossils of this guy, the Mesosaurus (a kind of lizard), are found in both South America and Africa.

fossilised remains of a plant that existed when coal was being formed are only found in India and Antarctica.

[a2geographyprocrastination]

1. Plate Movement - plate tectonics theory

1912 - Alfred Wegener.

  Creator of the theory of continental drift, stating that a supercontinent, Pangaea, existed about 300 million years ago.

He also said that Pangaea later split into two continents - Laurasia in the north and Gondwanaland in the south.