1. Earth’s Structure and Pangaea

2. Review Inside the Earth
The Earth has 4 layers.
Crust (rock)
Mantle (rock)
Outer Core (metal)
Inner Core (metal)

3. Continental Drift Theory
Continental Drift states that the continents were once a single landmass (Pangaea), broke apart, and “drifted” to their current locations.
Proposed by Alfred Wegener (1915).
He had evidence that Pangaea existed…
Lived in the early 1900’s

4. Pangaea Large single landmass that existed 245 m.y.a.
Evidence that Pangaea existed
Continents fit together like puzzle pieces (mountain ranges lined up)
Mesosaurus – Reptile fossil found on South America and Africa – It couldn’t swim!
Glossopteris – Tropical plant fossil that was found in Antarctica!
The continental drift theory was NOT accepted because Wegener could not explain HOW the continents were moving/drifted apart.

5. When magma is heated it becomes less dense and rises.

6. Why WERE the continents moving??
…because of sea-floor spreading!
Two oceanic plates pull apart, magma rises through the gap in the middle, the magma cools and forms new sea floor. (Oceanic crust)
Continents are connected to the sea-floor. When the sea-floor moves, so does the continents!

7. Sea-Floor Spreading Evidence
Brand new rock was found at the mid-ocean ridge.
Rock gets older and older the farther you get away from the ridge. Oldest rocks were found at the trenches.
Magnetic Reversals – Iron in the rocks switched directions every time the Earth’s polarity switched.

8. Sea-Floor Spreading in detail…

9. Check these sites out!