1. Learning Objectives
I can describe Alfred Wegener’s hypothesis of continental drift.
I can explain how sea-floor spreading provides a way for continents to move.
I can describe how new oceanic lithosphere forms at mid-ocean ridges.
I can analyze how magnetic reversals provide evidence for sea-floor spreading.

2. Ch.4, Sec.2 - Restless Continents
continental drift: the hypothesis by Alfred Wegener that states that the continents once formed a single landmass, broke up, and drifted to their present locations.
- many fossils & rocks
are found only on certain parts of certain continents.

3. Ch.4, Sec.2 - Restless Continents
- the continents slowly drifted away from Pangaea, which was the super-continent that existed 245 million years ago. (same time as dinosaurs)

4. Ch.4, Sec.2 - Restless Continents
sea-floor spreading: the process by which new oceanic lithosphere forms as magma rises toward the surface and solidifies.

5. Ch.4, Sec.2 - Restless Continents

6. Ch.4, Sec.2 - Restless Continents
- the best evidence of sea-floor spreading comes from magnetic reversals recorded in the ocean floor.
- iron in the newly formed rock at the mid-ocean ridges has a magnetic field that is slowly spreading across the sea floor & reversing the polarity.
- intervals occur once every 200,000 years on average

7. Ch.4, Sec.2 - Restless Continents

8. Ch.4, Sec.2 - Restless Continents
- geologists predict that the continents will continue to move into another supercontinent, called Pangaea Ultima, in 250 million years!

9. Ch.4, Sec.2 - Restless Continents

10. Ch.4, Sec.2 - Restless Continents

11. Exit Slip
How do magnetic reversal fields at oceans’ floors prove that the sea-floor is spreading?