1. Continental Drift

2. What is it?
Continental Drift - Earth’s continents were once joined in a single landmass, and gradually moved, or drifted apart.
People thought this for centuries - they began thinking this when the first maps were introduced to the world.
Alfred Wegener came up with the hypothesis of continental drift.

3. Fossil Evidence
The same fossils have been discovered in South America as well as in western Africa.
Mesosaurus - a reptile that lived in ancient time
Lived 270 million years ago
Fossils are only found in these two places

4. Climate Evidence Today, Greenland lies near the north pole.
There are fossils being dug up in Greenland that have ancient tropical plants.
How did tropical plants get to an area that is so cold and covered in ice?
South Africa is warm today?
South Africa has evidence that it was once covered by ice.

5. Geologic Evidence
The kinds of rocks on each continent can be matched to another continent.
The rock layers in Brazil match the rock layers in western Africa.
Rocks in the Appalachian Mountains match rocks found in Scotland.

6. Pangaea
With so much evidence that the continents were once connected, Wegener drew a conclusion.
The continents all were connected in a supercontinent that was named Pangaea.
Pangaea split apart 200 million years ago.

7. How do the continents move?
1950s - Scientists begin mapping the sea floor.
How would you think the sea floor would look?
They thought it would look smooth.
Scientists found mid-ocean ridges, or underwater mountains.

8. Mid-Ocean Ridges Form along cracks in the crust
Molten rocks rise though the cracks, cool, and the mountains are formed.
Newer rock comes out, and pushes the older rock away.
Scientists tested rocks and found that the youngest rocks were by cracks in Earth.
The oldest ocean rock is only billion years old.
The continents that we live on is about 4 billion years old.

9. If we keep getting new rock, why is Earth the same size?
Deep sea trenches
The older crust comes to a trench, and it sinks into the trench.
Old crust is destroyed at the same rate new crust is being formed; this is why we are not getting any bigger.
This proves that Earth is moving!

10. Why do plates move? Tectonic plates rest on the asthenosphere.
Rocks move by convection.
Convection - energy transfer by the movement of material
Hot softer rock rises, cools, and sinks, process starts again and again
This is called a convection current.
These convection currents are present in the mantle.

11. Plate Tectonic Theory
Theory of plate tectonics - The lithosphere is made up of huge plates that move over the surface of the earth
Plates move over a long period of time in three main ways
Past each other
Move apart
Push together
Earthquakes, volcanoes, and mountain ranges occur when the plates run into each other.