1. Developing the Theory of Plate Tectonics

2. Alfred Wegener was a meteorologist studying the atmosphere.

3. 1911:
Wegener noticed the continental edges look like they fit together.
Found papers describing identical fossils of plants and animals found on opposite sides of the ocean.

4. 1911-1915: Found descriptions of many matching geological features on different continents.
Coal deposits in non-tropical places
Glacial remains span two continents
Matching Mountain Ranges on opposite continents.
Others

5. 1915: Published The Origin of Continents and Oceans, which outlines his idea of continental drift.
Earth's continents were once all together in a supercontinent called Pangaea. Pangaea broke apart and the continents have been moving ever since.
Other scientists reject it, mostly due to his inability to explain how the continents move.

6. 1930: Alfred Wegener dies.

7. 1940s: World War II brings detailed maps of the ocean floor that reveal the mid-ocean ridges.

8. 1950s: Scientists study the mid-Atlantic ridge
1950s: Scientists study the mid-Atlantic ridge. Rocks in the middle are newest and get older further out.

9. Scientists also find alternating strips of rocks with identical magnetic polarity on each side of the ridge. Igneous rock's properties align with Earth's magnetic field as it cools. Since Earth's magnetic field reverses from time to time, alternating bands of rocks are found on both sides of the Mid-Ocean Ridge.

10. Scientists discovered that many earthquakes found concentrated in areas that outline parts of the Earth's crust. These pieces of the crust were called "plates."

11. “Plates” Move
The circular motion of the softened material in the mantle (convection) drags plates.
As old crust is pulled under newer crust when two pieces collide, the gravity pulls that crust along, something called Slab Pull.

12. Evidence Wegener used to develop the theory of continental drift:
1. Continental shape looks like they would fit together.
2. Identical fossils found on different continents.
3. Glacial deposits and other landforms spanning multiple continents.

13. Evidence Hess had to develop his theory of sea-floor spreading:
4. Map of the ocean bottom shows the age and magnetic polarity of the rock are symmetrical at sea-floor spreading areas.

14. The Theory of Plate Tectonics:
New evidence used to develop
The Theory of Plate Tectonics:
5. Location of Earthquakes and Volcanoes is not random; we use those locations to describe the locations of each of the boundaries.

15. The Theory of Plate Tectonics
Earth's lithosphere (crust and top of the mantle) is divided into sections, called plates, that move because of the convection currents in the mantle caused by the internal energy of the Earth.