Topic 4: The Moving Crust http://www.learner.org/interactives/dynamicearth/index.html

Antarctica is a frozen land, so cold and icy that no trees can grow there. Yet scientists have discovered fossils of ancient trees in Antarctica What do you think this means?

The Himalayas (central Asia) are the tallest mountains in the world The Himalayas (central Asia) are the tallest mountains in the world. But fossils of seashells can be found high in these mountains, far from any ocean How do you think they got there?

Have the continents always looked this way?

How well do the continents fit together? Is it a perfect fit?

If the continents were fixed in place, why do they look as though they could be joined? Supercontinent At one time, the continents had been joined together in a large single land mass Pangaea

Since the time of Pangea, the continents have slowly drifted apart CONTINENTAL DRIFT Started about 200 million years ago and is still continuing today

What evidence supports this hypothesis? 1. Biological Fossils of the same plants & animals were found on different continents

2. Geology Rocks found on either side of the Atlantic Ocean were similar in formation, age and other properties

3. Climate Coal is formed in warm, swampy climates Coal beds in North America, Europe, & Antarctica seem to be connected

4. Glacial Deposits Rocks moved and laid down by glacier movement Found spread over the southern hemisphere Grooves under the glaciers show the direction the glaciers moved

Plate Tectonics The Earth’s crust is divide into large, irregular pieces TECTONIC PLATES Plates are always moving on Earth’s MOLTEN mantle http://www.cbc.ca/news2/interactives/world-quakes/

3 ways plates can move: Converge Two plates pushing together Creates ridges Form subduction zones One plate passes below another Diverge Two plates pulling apart Creates trenches (openings)

Transform / Shear Plates slide past each other in opposite directions

Why do tectonic plates move? Convection currents Flow resulting from the warmer materials of the Earth’s core rising and then sinking as it cools