1. CONTINENTAL DRIFT

2. The Story of Alfred L. Wegener
There once was a German Geologist who noticed similar rocks & fossil remains were found on continents which seemed to fit together
He called this “super” continent called Pangaea
In 1912 Wegener published the first version & died defending his theory

3. PANGAEA
the large landmass that included all of Earth’s present day continents

4. WEGENERS CONTINENTAL DRIFT
Alfred Wegener in the early 1900’s proposed the hypothesis that continents were once joined together in a single large land mass he called Pangaea (meaning “all land” in Greek).

5. WEGENERS CONTINENTAL DRIFT
He proposed that Pangaea had split apart and the continents had moved gradually to their present positions - a process that became known as continental drift.

6. Pangaea about 200 million years ago, before it began breaking up
Pangaea about 200 million years ago, before it began breaking up. Wegener named the southern portion of Pangaea Gondwana, and the northern portion Laurasia.

7. The continents about 70 million years ago
The continents about 70 million years ago. Notice that the breakup of Pangea formed the Atlantic Ocean. India’s eventual collision with Eurasia would form the Himalayan Mountains.

8. The position of the continents today
The position of the continents today. The continents are still slowly moving, at about the speed your fingernails grow. Satellite measurements have confirmed that every year the Atlantic Ocean gets a few inches wider!

9. Support for Continental Drift
1. SHAPE of the continents
Continents fit together like puzzle pieces

10. Support for Continental Drift
1. SHAPE of the continents
Wegener was not the only one to notice the fit of the continents.
1858: Antonio Pelligrini depicted Africa and South America connected.
He was one of the first scientists to publish maps depicting the apparent fit of the continents.

11. Support for Continental Drift
2. FOSSIL EVIDENCE
SAME FOSSILS: DIFFERENT CONTINENTS
Mesosaurus was incapable of swimming across a large ocean.

12. Evidence for Continental Drift
Lystrosaurus: mammal like reptile, herbivore, about the size of a small dog.
Mesosaurus: freshwater reptile, carnivore.
Glossopteris: extinct seed fern was about 12 ft (3.6 m) tall.
Cynognathus: metre-long predator of the Lower Triassic. It was one of the more mammal-like of the "mammal-like reptiles",

13. Support for Continental Drift
3. ROCK EVIDENCE – Mountain ranges
SAME ROCK: DIFFERENT RANGE Existing mountain ranges separated by vast oceans contain rocks of identical mineral content.
A prime example are the Appalachian Mountains in the eastern U.S and the Caledonian Mountains in the British Isles.

14. Support for Continental Drift
3. ROCK EVIDENCE – Mountain ranges
Rock sequences (meaning he looked at the order of rock layers) in South America, Africa, India, Antarctica, and Australia show remarkable similarities.
Wegener showed that the same three layers occur at each of these places.
Picture from

15. SAME SCARS: DIFFERENT CONTINENTS
Support for Continental Drift
4. GLACIAL SCARS/ CLIMATE CHANGE
SAME SCARS: DIFFERENT CONTINENTS
The land area that shows evidence of this glaciation now lies near the equator in a subtropical or tropical climate.

16. Support for Continental Drift
5. LOCATION OF Coal Deposits/ climate change
Large tropical swamps existed during the same time in the Northern Hemisphere with lush vegetation which eventually became the coal fields of the eastern U.S., Europe, and Siberia.

17. 5. LOCATION OF Coal Deposits/ climate change
Support for Continental Drift
5. LOCATION OF Coal Deposits/ climate change
Coal deposits have been found in temperate and polar regions; however, coal is formed in tropical regions.

18. CONTINENTAL DRIFT IN DOUBT
Why didn’t people believe in continental drift?
People couldn’t image how the earth could be millions of years old
People couldn’t image a force great enough to move the continents
Wind and currents could possibly move fossils
Theory was not accepted by scientists

19. CONTINENTAL DRIFT IN DOUBT
Everyone agreed that Wegener’s evidence was compelling. But wouldn’t we feel the movement?
Also, wouldn’t there be evidence to show that the continents were still moving today?
Wegener was a meteorologist and his theory was not well accepted. (He died on an expedition in Greenland collecting ice samples)
BUT by the 1960’s evidence would prove continental drift is TRUE and…. The story continues (as does all good science!)

20. Seafloor Spreading
One reason scientists had a hard time with Wegener’s theory is that there was no mechanism for the continents motion.
Then comes along seafloor spreading!

21. Seafloor Spreading
In the 1960’s, a scientist named Henry Hess made a discovery that would vindicate Wegner.
Using new technology, radar, he discovered that the seafloor has both trenches and mid-ocean ridges.
Henry Hess proposed the sea-floor spreading theory.
Picture from USGS

22. Seafloor Spreading
Hess proposed that hot, less dense material below Earth’s crust rises toward the surface at the mid-ocean ridges.
Then, it flows sideways, carrying the seafloor away from the ridge in both directions.
Picture from

23. Seafloor Spreading
As the seafloor spreads apart at a mid-ocean ridge, new seafloor is created.
The older seafloor moves away from the ridge in opposite directions.
This helped explain how the crust could move—something that the continental drift hypothesis could not do.

24. Evidence for Spreading
In 1968, scientists aboard the research ship Glomar Challenger began gathering information about the rocks on the seafloor.
Scientists found that the youngest rocks are located at the mid-ocean ridges.

25. Mechanism for Plate Tectonics
Seafloor Spreading provided insight to the mechanism for how the continents moved.
The magma which pushes up at the mid-ocean ridge provides the new land pushing the plates, and the subduction zones gobble up the land on the other side of the plates.
Picture from
The mechanism that made continental drift was convection currents!

26. Plate Tectonic Theory
Both Hess’s discovery and Wegner’s continental drift theory combined into what scientists now call the Plate Tectonic Theory.
Theory of plate tectonics:
The Earth’s crust and part of the upper mantle are broken into sections, called plates which move on a plastic-like layer of the mantle

27. Tectonic plates move. The boundaries created where they meet are called FAULTS

28. Three types of plate boundary
Divergent
Convergent
Transform
Firstly, there are three types of plate boundary, each related to the movement seen along the boundary.
Divergent boundaries are where plates move away from each other
Convergent boundaries are where the plates move towards each other
Transform boundaries are where the plates slide past each other.
Presenter: See diagrams for each - it is important to remember the names of the boundary types and the motion involved.

29. Rift Valleys are areas where the crust is pulling away slowly.
There are three types of plate movement boundaries
1. Divergent
Also known as seafloor spreading
Plates are separating from each other as a new land mass forms
This is seen at mid-ocean ridges and rifts
Plate separation is a slow process. For example, divergence along the Mid Atlantic ridge causes the Atlantic Ocean to widen at only about 2 centimeters per year.
Picture from
Author Hobart M. King
Rift Valleys are areas where the crust is pulling away slowly.

30. There are three types of plate movement boundaries
2. Convergent
Two continental plates collide. & crumple the edges of the plates & form mountains.
We can see the end result of the collision between the Indian & Eurasian plates which are the Himalayan Mountains.
Picture from USGS
Picture from Author Hobart M. King

31. Continent-Oceanic Crust Collision
SUBDUCTION is another type of a convergent plate movement.
At a convergent boundary where continental crust pushes against oceanic crust, the oceanic crust which is thinner and more dense than the continental crust, sinks below the continental crust.
This is called a Subduction Zone.
The oceanic crust descends into the mantle at a rate of centimetres per year. This oceanic crust is called the “Subducting Slab” (see diagram).
When the subducting slab reaches a depth of around 100 kilometres, it dehydrates and releases water into the overlying mantle wedge (Presenter: explain all of this using the diagram).
The addition of water into the mantle wedge changes the melting point of the molten material there forming new melt which rises up into the overlying continental crust forming volcanoes.
Subduction is a way of recycling the oceanic crust. Eventually the subducting slab sinks down into the mantle to be recycled. It is for this reason that the oceanic crust is much younger than the continental crust which is not recycled.

32. Subduction
Oceanic crust and lithosphere subducts underneath the continental crust and lithosphere
Oceanic lithosphere heats and dehydrates as it subsides
The melt rises forming volcanism
E.g. The Andes
The Andes mountain range along the western edge of the South American continent is an example of a mountain belt formed by subduction.
The continental crust of the South American plate has buckled under the compressional strain of converging with the Nasca and Antarctic plates. Additionally there are many volcanoes, the result of melting of the subducting slab and the production of new material that has risen through the crust to the surface.

33. Ocean-Ocean Plate Collision
When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone.
The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench.
The worlds deepest parts of the ocean are found along trenches.
E.g. The Mariana Trench is 11 km deep!
When two oceanic plates converge, because they are dense, one runs over the top of the other causing it to sink into the mantle and a subduction zone is formed.
The subducting plate is bent down into the mantle to form a deep depression in the seafloor called a trench.
Trenches are the deepest parts of the ocean and remain largely unexplored.

34. There are three types of plate movement boundaries
3. Transform
Two plates slide past each other
Example: San Andreas Fault in California
Picture from
Author Hobart M. King

35. Transform
Convergent
Divergent

36. Plate Tectonic Theory Plate Tectonics explains Earthquakes Mountains
Volcanoes