Plate Tectonic Theories

Continental Drift, Sea Floor Spreading, and Plate Tectonics

Alyssa Clayton

Continental Drift

Evidence Exhibit A: The coastlines of different continents fit together like a puzzle.

Evidence Exhibit B: Fossils of plants and animals were found on continents where they could not have existed.

Continental Drift Presentation


A dutch mapmaker was the first to notice how the coast lines of South America and Africa fit together, but Alfred Wegener was the first to come up with the idea of Pangaea. The problem was, his only evidence was that the continents fit together like a puzzle.

The fossils of warm weather plants were found on a cold-weather continents. The fossils of a fresh-water reptile called Mesosaurus was found on a continent it could not have lived on, and the reptile did not swim there, because of the salt-water. The only explanation is that all the continents were together at one time, and the animals/plants lived in one area.

Sea Floor Spreading

Evidence Exhibit A: Young and old rocks were found on the ocean floor.

Evidence Exhibit B: Magnetic pole reversals were in the rocks on the ocean floor.

Summation: Young rocks were more towards the center of the ocean. Older rocks were near the outside of the ocean. Therefore, the oceanic crust was being pushed back, and became older. The young rocks were just formed near the center by the magma rising and pushing the crust away.

Over time, the magnets in the rocks would switch back and forth, going N-S-N-S. This proved that the plates were slowly being pushed away, otherwise, the rock would all be either North or South.

Seafloor Spreading Presentation

Plate Tectonics

Evidence Exhibit A: Convergent boundaries create mountains and subduction zones.

Evidence Exhibit B: Divergent boundaries create rifts and volcanoes.

Summation: Convergent boundaries push together, so they create mountains when it is two continental plates. But when an oceanic and a continental plate push together, they create a subduction zone because the oceanic goes underneath the continental plate.

Divergent boundaries pull apart from each other, so the create rifts when they come apart. Sometimes they create volcanoes because there is magma trying to escape from underneath, so when the two plates pull apart, it comes up as a volcano.

Plate Tectonics Presentation