1. Continental Drift and Sea Floor Spreading

2. Tectonic Plates!

3. Plate Tectonics
The term tectonics is Greek. Coming from the word “tektonikos” meaning of a builder.
They are pieces of the lithosphere that move around.
They fit together like a jigsaw puzzle.
Float on top of the mantle similar to ice floating on water.

4. Continental Drift
Alfred Wegner claimed that the continents were once a single land mass that drifted apart.
Started as a single supercontinent called Pangea.
There are four main pieces of evidence that support Wegner’s claim.

5. Evidence Claim Number 1 – Geographic Fit
Pieces “fit together like a puzzle”

6. Evidence Claim Number 2 – Geologic Rock Structures.
The Mountains in Africa and the Mountains in Argentina, South America are the same type.
These mountain chains match up when the ends of the continents are joined.

7. Evidence Claim Number 3 – Fossil Evidence
Fossils of the same plants and animals are found in different continents that do not touch currently.

8. Evidence Claim Number 4 – Geographical Oddities
Coal deposits in Antarctica. (plant life needed to make coal).
Antarctica would have had to be located closer to the equator.
Glacial Deposits in Africa.
Africa would have had to be located further from the equator at that time.

9. Sea Floor Spreading

10. Sea Floor Spreading
In 1960 Harry Hess studies Wegner’s theory of continental drift.
He proposes the idea that the ocean floors move like conveyer belts, which causes the continents to move.

11. Sea Floor Spreading He called this idea sea floor spreading.
The ocean floor spreads out at the Mid-Ocean Ridge.
New material is added on either side of the ridge.
There are three forms of evidence for sea floor spreading.

12. Evidence 1 – Molten Material
Scientists found pillow rocks on the ocean floor.
These are made from molten material that has cooled quickly.
This is evidence that molten material has erupted again and again along the mid ocean ridge.

13. Evidence 2 – Magnetic Stripes
The earth is like a giant magnet with a north and south pole.
The Earth’s magnetic pole reversed themselves every 780,000.
Rocks on the ocean floor are in a pattern of magnetized stripes.
These stripes show when the Earth reversed its magnetic field.

14. Evidence 2 – Magnetic Stripes Continued
Molten material contains iron.
As it cools the iron bits line up in the direction of the magnetic poles
When the rock hardens, the iron is locked into place giving them a permanent “magnetic memory.”
Magnetic memory is symmetrical across the mid ocean ridge.

15. Evidence 3 – Drilling Samples
Scientists studied the age of rocks they sampled from the ocean floor.
They found that the farther from the ridge, the older the rock.
The closer to the center of the ridge the younger the rocks were.
Evidence 3 – Drilling Samples