1. Continental Drift
By: Ms. R. Wallace, WFHS

2. The continents! As accurate maps were developed,
people noticed the continents fit together like puzzle pieces.

3. The Earth Moves!!
Alfred Wegener (1912) proposed that the continents were joined together in the past and broke apart about 200 million years ago.
Was rejected by scientific community.
Continental Drift: continents have moved horizontally to their current location

4. Pangea

5. Evidence for Continental Drift
Fossil and climate clues
fossils like Mesosaurus (reptile) and Glossopteris (fern) were found on different continents
Warm weather fossils indicate similar climates

6. Evidence Continued Structural (Rock) clues
Similar rock structures were found on different continents
Ex. Coal fields, glacier deposits, folded mountains

7. Sea Floor Spreading
Marie Tharp – first scientific map of the entire ocean floor (including mid-atlantic ridge)
Harry Hess – worked on sea floor spreading and helped develop theory of plate tectonics

8. Sea floor spreading!
They suggested that mid-ocean ridges (underwater mountain chains) were formed when hot, less dense material in the mantle (2nd layer of the Earth) is heated and carries the seafloor ways from the ridge.

9. This is called RIDGE PUSH and Gravity Pull

10. Age Evidence
Rocks in the seafloor are much younger than on the continents and the youngest rocks are at the center of mid-ocean ridges

11. Youngest rock in RED!

12. Magnetic Clues called Paleomagnetism
The Earth’s core creates a magnetic field and periodically (around every 500,000 to 1,000,000 years) reverses polarity.

13. Paleomagnetism
For example all rocks that form from cooling magma will be magnetized with north pole (magnetic north). When the magnetic field switches, rocks would crystallize and have a magnetism that lines up with the South Pole (magnetic south).

14. Paleomagnetism

15. Magnetic Pole Reversal
Rocks in the ocean show many magnetic reversals proving that new rock was being formed at mid-ocean ridges.
BiorYRNU