1. Continental Drift and Seafloor Spreading
Restless Continents
Continental Drift and Seafloor Spreading

2. Continental Drift
The hypothesis that states that the continents once formed a single landmass, broke up, then drifted into their present locations.
This massive, collective landmass was called PANGEA…

3. ALFRED WEGNER
German scientist; Proposed the most famous version of the continental drift theory, (but he could not explain why or how the continents drifted apart.)
His evidence included:
Continental Puzzle
Matching Fossils
Rocks Types and Structure
Ancient Climates

4. Continental Puzzle

6. Fossilized Evidence
Continental Drift explains why fossils of the same plant and animal species are found on continents that are on different sides of the Atlantic Ocean.
Many of these ancient species could not have crossed the Atlantic Ocean.
This is hard to explain without the theory of Continental Drift

7. Fossilized Evidence
Also found on different continents are evidence of the same ancient climate conditions:
Same rocks
And fossilized plants

8. The Breakup of Pangea
Wegner believed Pangea existed 245 million years ago.
Pangea further split into two continents – Laurasia and Gondwana – about 180 million years ago.
These two continents split again, forming the continents we know today.

9. Many did not accept Wegner’s theory of continental drift…until the theory of plate tectonics and seafloor spreading came about!

10. Mid-oceanic Ridges and Seafloor Spreading
Sea-floor Spreading: The process by which new oceanic lithosphere forms as magma rises toward the surface and solidifies.
As the tectonic plates move away from each other, the sea floor spreads apart, and magma fills in the gap.
As new crust forms in the ridge, older crust gets pushed away. (hence, the further away crust is from the ridge, the older it is)

11. Seafloor Spreading Video

12. Magnetic Reversal – evidence of sea-floor spreading
Throughout Earth’s History, the North and South magnetic poles have changed places many times.
The poles flip, which causes the Earth’s polarity to flip.

13. Magnetic Reversal – evidence of sea-floor spreading
The molten rock at the mid-ocean ridges contains tiny grains of magnetic minerals (these minerals align with the Earth’s magnetic field).
When the magnetic field reverses, the minerals align in the opposite direction.
As the sea-floor spreads, it carries these magnetic minerals with it, creating a record of Earth’s polarity.

14. Magnetic Reversal