1. Continental Drift

2. Alfred Wegener
Alfred Wegener - German scientist who presented his ideas on continental drift to the scientific community in 1912.
The evidence that he presented included: the puzzle like fit of the continental coastlines, evidence from rock formations, fossil evidence and ancient climate evidence.

3. 1) Puzzle-like fit of continental coastlines
Wegener was not the first to notice this phenonmenon – he was the first to present his ideas that the continents moved with evidence.

4. . . . This came from his idea about a supercontinent which existed, called “Pangaea”

5. 2) Evidence from Rock Formations
There are rock formations that are older than 200 million years located in the Appalachian mountains, Greenland and Europe. This strengthened the argument that the landmasses were once connected.

6. 3)Fossil Evidence
Mesosaurus Dinosaur: Found in Africa and S. America – there is no
way it could have swam!
Dinosaurs from Dino Cove liked the Subzero temperatures.

7. Glossopteris – a seed fern found on several continents that today have different climates. Their seed pods are too big to have blown to all the different places. These ferns grow in tropical climates, so this shows that the places where the fossils were found were at one time near the equator

8. 4)Ancient Climate Evidence
Coal Beds
Glacial Deposits
Coal is formed in wet, swampy climates
Coal beds found in Antarctica indicate that this continent must have been in a different position 200 mya.
We see evidence of glacial deposits in Africa, India, Australia and S.America. This shows that these areas must have been closer to the poles in the past.

9. Wegener’s Hypothesis is Rejected!
Even though Wegener had evidence, he did not provide a mechanism for HOW the continents move. He thought that the Earth’s rotation might move the continents through the oceanic crust.
Other scientists showed that the Earth’s rotation does not provide a strong enough force to move continents. Also, if continents moved through a stationary ocean floor, we would see evidence of crustal shattering (which we do not).

10. Other scientists showed that the Earth’s rotation does not provide a strong enough force to move continents. Also, if continents moved through a stationary ocean floor, we would see evidence of crustal shattering (which we do not).
MODERN THEORY #1: Convection currents in the mantle roll the plates along like a conveyor belt!

11. MODERN THEORY #2: “Slab-Pull” Plates will sink from density, are pulled down by gravity, and sucked in by the gooey mantle

12. These Modern Theories (and others) made the current Theory of Plate Tectonics
New evidence in the 1950’s would provide the mechanism for Alfred Wegener’s hypothesis. The Theory of Plate Tectonics evolves:
The crust is broken into pieces called “plates”
The plates move around on top of the molten mantle in different ways.