1. EVIDENCE OF
CONTINENTAL DRIFT

3. Wegener’s Continental Drift Hypothesis
States that the continents once formed a single landmass, broke up, and drifted to their present locations.
His evidence includes:
Shape of the continents
Fossil evidence
Similar rocks

4. The shape of some of the continents look like they could fit together like …

5. …Puzzle Pieces

6. Fossils of the same species are found on two different continents.
Fossil Evidence
Fossils of the same species are found on two different continents.

9. Rock type and structure correlation

10. Coal Deposits

11. Glacial Deposits

12. Wegener had a lot of evidence…

13. …so why was his hypothesis almost universally rejected?
He could not satisfactorily explain the forces moving the continents.
Scientists could not explain how the continents were moving.
Flaws in Wegener’s data had the continents moving much to far and too fast.

14. Pangaea
The large land mass was called Pangaea.

17. Continental Drift - animation

19. Mid-Ocean Ridges and Sea-Floor Spreading
Mid-ocean ridges are places where
sea-floor spreading takes place.

20. Mid-Ocean Ridges and Sea-Floor Spreading
As the tectonic plates move away from each other, the sea floor spreads apart and magma fills the gap.

21. As the new crust forms, the older crust gets pushed away from the mid-ocean ridge.
This means that the older crust is farther away from the mid-ocean ridge than the younger crust is.

22. Evidence for Sea-Floor Spreading: Magnetic Reversals
Throughout Earth’s history, the north and south magnetic poles have changed places many times.

23. Magnetic Reversal of Earth’s Poles

24. Magnetic Reversals and Sea-Floor Spreading
The molten rock at the mid-ocean ridges contains tiny grains of magnetic minerals like iron.
These minerals align with the magnetic field of the Earth while liquid, then when they cool and harden, they make a record of the magnetic poles.
This record is then carried slowly away from the spreading center of the ridge as sea-floor spreading occurs.

25. Magnetic Reversals and Sea-Floor Spreading