1. The Restless Continents

2. Have you ever looked at a map of the world?
Did you notice how the coastlines of continents on opposite sides of the oceans appear to fit together like the pieces of a puzzle?

3. Is this a coincidence?
How is it that the coastlines fit together so well?
Is it possible that the continents were actually together sometime in the past?

4. Wegener’s Continental Drift Hypothesis
One Scientist who looked at the pieces of this puzzle was Alfred Wegener in the early 1900’s
He wrote about his hypothesis: Continental Drift

5. Continental Drift
The hypothesis that the continents once formed a single landmass, broke up, and drifted to their present locations.

6. Continental Drift explained a few puzzling questions
Why do the continents seem to fit together like a giant puzzle?
Why are fossils of the same plant and animal species found on continents that are on different sides of the Atlantic Ocean?
Mesosaurus – SA, Africa
Glossopterous –Antartica, Africa, Australia
Why are rocks with different magnetic alignments found in the same place (paleomagnetism)?

7. The Hypothesis
Wegener made many observations before proposing his hypothesis of continental drift.
He thought that all the present continents were once joined in a single, huge continent called Pangaea

8. Pangaea “Pangaea” means “all earth”
It existed about 245 million years ago
It split into two huge continents about 180 million years ago
Laurasia
Gondwana
These two continents split again about 65 million years ago to form the continents we know today

9. But Wegener’s theory of continental drift was not widely accepted during his lifetime….
Many scientists would not accept his hypothesis.
They said that the calculated strength of the rocks that make up the Earth’s crust would not allow the crust to move in that way.
Many years later, other evidences were presented that supported his theory.

10. What do you think… Our continents will look like in the future?
Will we move back together?
Will we be further apart?
What evidence will future scientists use to show our current day locations?

11. Demonstration of Sea Floor Spreading
Fold your 1 meter of paper in half to form a “V”
Slide the paper between two tables. Have them close enough to grip the paper, but far enough apart so that the paper can slide through the crack.
Using the ruler, slide the paper out 10 cm one each side.
Draw a vertical line on the paper at the table’s crack. Label this area “1” on both sides of the paper
Measure out 10 more cm, draw your line and label this area “2”on both sides of the paper
Continue this until you have 5 sections on each side

12. The Restless Planet: Sea Floor Spreading
Unit 2: Sixth Grade

13. So what did Wegener believe was moving the continents?
Sea-floor Spreading !
It was proposed that as the tectonic plates move apart, it creates a rift that allows magma to rise to the surface of the ocean floor and solidifies.
Mid-Ocean ridges are places where sea-floor spreading takes place
Mid-Atlantic Ridge
This creates new crust in that area, further pushing the continents apart.
Evidence: older crust is farther away from the mid-ocean ridge than newer crust is.

14. Sea-Floor Spreading http://www. youtube. com/watch

15. Mid-Atlantic Ridge

16. Debate
We will be debating the most compelling evidence to support the theory of continental drift.
There will be three groups.
Group 1: Fossil Similarities
Group 2: Landform Similarities
Group 3: Sea Floor Spreading
You will have 20 minutes to form your argument.
Use notes, ITs, netbooks to find info
Write your points on the construction paper as bullets
Groups will then present their arguments to the class

17. Other evidence to support continental drift
Stratigraphy: studying the layers of the Earth, showed that the geologic columns in Antarctica and India were similar
Glaciation: Glacial deposits in Canada were also found in India and southern Africa
Marine Corals
Mountain Belts: ancient mountains in South Africa and near Buenos Aires, Argentina align when the two continents are fitted together.

18. More evidence to support Sea-Floor Spreading
Magnetic Reversals
Throughout Earth’s history, the north and south poles have changed places many times.
The molten rock at the mid-ocean ridges contains tiny grains of magnetic minerals.
They act as compasses, lining up with the magnetic field of the Earth.
When the magma cools, these tiny compasses are preserved in the rock.
When the poles reverse, the mineral grains are aligned in with the “incorrect” pole.
Paleomagetism

19. Magnetic Reversals