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Continental Drift

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Clare Chiu

on 8 May 2010

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Transcript of Continental Drift

Continental Drift: it's true! by Clare & Katie ~The continents looked as though they might fit together like puzzle pieces.
*The continental shelves actually fit together even better.

~The original supercontinent was named Pangaea by Wegener.
*'pan means all and 'gaea means earth.

~Wegener also realized that other evidence also supported his theory.
*There were matching geologic features and rocks on different continents.
*There were matching fossils, like Mesosaurus, on different continents.
*There was evidence of different climates, (eg. Such as glaciers) on warm continents. Early maps of the world caused Wegener to propose the continental drift theory. Like pieces of a jigsaw puzzle, the continents
fit together into one, large whole. How can continents move?? Wegener’s evidence for continental drift did not explain how entire continents could change locations. ~New scientific equipment allowed scientists to measure the slow but steady drift of Earth’s tectonic plates.
~It was noted that earthquakes and volcanoes appear in certain patterns along the edges of tectonic plates.
~Mapping of the ocean floor revealed the Mid-Atlantic Ridge, a long mountain range running down the middle of the Atlantic Ocean.
~Rocks taken from the Mid-Atlantic Ridge were younger than other ocean rocks.
~Sediments along the ridge became thicker farther away from the ridge.
~Paleomagnetism shows that iron-based rocks along the ridges are striped with reversing magnetic fields. Volcanoes are frequently found on boundaries between tectonic plates. Sea Floor Spreading: An explanation ~Magma (melted rock) rises and falls like warm and cold liquids.
~The convection currents of magma formed a spreading ridge where they broke through Earth’s crust.
*Like a “new crust” conveyer belt
*Magnetic striping of basalt rock shows long stripes of new rock moving away from ocean ridges and also reveals the direction of Earth’s magnetic field at that time. Hess suggested that magma rose to form new rock at certain places. Wilson then unified the ideas of Wegener and Hess into the plate tectonic theory. ~Continental drift occurs because of areas like these ridges that push along tectonic plates floating on Earth’s surface.
~Geologic hot spots are anywhere magma rises to Earth’s surface. Evidence of continental drift Fossils of Mesosaurus (yellow) have been found in only two places: southeastern South America and southwestern Africa.

Because Mesosaurus was a small, freshwater animal, it seemed unlikely the animal would have survived crossing the 6000 km of open ocean between the two continents The Cynognathus (red) and Lystrosaurus (orange) are also land animals could not have swum across miles of miles of open ocean.

The existence of Pangaea seemed the best explanation for the fossil findings: members of the same species would have been separated when the giant landmass broke apart. Another interesting example was the Glossopteris (green), a fern.

Wegener could not understand why fossils of this plant would be found so widely spread apart, from South America and Africa to Australia, India, and Antarctica. Ferns do not grow in cold climates, and there was no evidence that, 200 million years ago, polar climates were milder.

If, however, the continents were once joined as Pangaea, the location of the fossilized ferns made sense: In the past, Antarctica must have been closer to the equator and thus had a warmer climate. Since then, Antarctica has moved to its present location at the South Pole. He noted mountain ranges that begin on one continent, end at the coastline, and then appear to continue on a continent across an ocean.

There are also many similarities between rock structures, such as folds, and the ages of rocks on continents that are separated by thousands of kilometres of ocean.
*For example, rocks found in Newfoundland are the same type and age as rocks found in Greenland, Ireland, Scotland, and Norway.

Wegener reasoned that the world’s major mountain ranges would have been continuous when the continents were joined as Pangaea. Wegener’s analysis of rocks and mountain ranges supported his idea that the continents were once joined. -Evidence of glaciers were found in parts of the world that are now tropical, such as parts of India and Africa

*PALEOGLACIATION refers both to the extent of ancient glaciers and to the rock markings they have left behind.

-Coal deposits in Antarctica.
More evidence found by other scientists...
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