1. Evidence of Plate Tectonics
Continental Jigsaw
Fossils
Rocks
Climate

2. E.S. Plate Tectonic Notes
Continental Drift
Alfred Wegener, in 1912 noticed that the continental shorelines on either side of the Atlantic looked like they would fit together.
Wegener did not believe this was a coincidence and developed a hypothesis called Continental Drift.

3. Continental Drift “JIGSAW”
Hypothesis stated that the continents were once a part of a single land mass which he named Pangaea.
The northern hemisphere is called Laurasia and the southern called Gondwanaland.

4. Continental Drift The large ocean is called Panthalassa.
Wegener believed that 200 million years ago Pangaea began to break apart.
He believed that the continents drifted to their present positions creating mountains.

5. FOSSIL Evidence supporting Continental Drift
Fossils of mesosaurus had been found in eastern South America and western Africa.

7. ROCK Evidence supporting Continental Drift
The type of rocks in western Africa and eastern Brazil were the same.
The Caledonian
and Appalachian Mountains line up when North America and Europe are placed next to each other.

8. CLIMATE Evidence supporting Continental Drift
There is evidence that there were glaciers in southern Africa.
Today southern Africa has tropical climates.

9. Despite all of this evidence, continental drift was the laughing stock in the scientific community because Wegener could not describe what would cause the continents to drift over solid rock.

10. New Evidence
Seafloor Spreading- In 1947 scientists mapped out the Mid-Atlantic Ridge --an undersea mountain range.

11. New Evidence
These scientists discovered that the ocean floor is relatively young compared to the age of the continental rocks.
The mountain ranges were found to be volcanic.

12. Seafloor Spreading
Harry Hess hypothesized that there might be magma welling up from beneath this ridge. This would push rocks away from the ridge, making the rocks older farther away from the ridge.

13. Seafloor Spreading
These scientists needed proof for their hypothesis to be accepted.
These ocean rocks were radiometrically dated and found to get older away from the ridge.

14. Plate Tectonics
Later, information about the interior of the earth was discovered by studying earthquake waves.
We now have a theory called Plate Tectonics.

15. Plate Tectonics
the lithosphere (crust) of the earth is divided into plates which float on and travel over the mantle.

16. Differences Between Continental & Oceanic Lithosphere
younger (180 million years or less)
more dense
~7 km thick
Continental –
older (4 billion years
old)
less dense
~35-40 km thick