Evidence of the Plate Tectonic Theory

What is the Plate Tectonic Theory?

The Theory of Plate Tectonics states that the rigid, outer layer of the Earth (the lithosphere) is divided into a couple of dozen plates that move around on the surface of the Earth.

How did this theory come to be? The Plate Tectonic Theory is fairly new (only

about 90 years old).

Alfred Wegner was the first scientist to present the idea that the Earth’s plates are moving and were once a Supercontinent. He called this supercontinent, “Pangaea”. This idea of continental drift is also known as the Supercontinent Theory.

Of course there were many “haters” at the beginning, but now most consider this theory to be true based on EVIDENCE.

What is EVIDENCE?

Evidencenoun \ˈe-və-dən(t)s

- Something that furnishes proof.- A thing helpful in forming a conclusion.

How could you define evidence in your own words?

Evidence #1: Puzzle Pieces The first piece of evidence

noticed by Wegner was that the edge of continental shelves fit together like puzzle pieces.

• Wegner was not the first person to notice these similar edges. In fact, many old explorers had also noticed this on their maps.

Evidence #2: Fossils Paleontologists also found that there were

fossils of similar species found on continents separated by great distances.

For example, how could you explain finding the fossils of a small hen that could not fly in both Massachusetts and England?

The only explanation found by scientists is that the plates are slowly drifting apart over geologic time.

Evidence #3: Rock Layering

A third piece of evidence is found through the layers of rock under the Earth’s surface. Rocks that were formed at different places around the globe have different magnetizations (the amount of magnetic power a rock has). By using this information, when rock layers were uncovered with similar magnetization patterns as rocks in other continents, geologists became more convinced of some type of plate movement.

Evidence #4: Seafloor Spreading Seafloor spreading occurs at divergent

boundaries on the ocean floor where new oceanic crust is formed from volcanic activity.

Geologist have tested the oceanic crust at these boundaries and determined that the crust near the rift valley is much younger than that further away from the boundary.

Seafloor Spreading:The Mid-Atlantic Ridge

• The Earth’s longest mountain chain isn’t the Andes in South America, the Himalayas in Asia, or even the North American Rockies!! It is an underwater mountain chain that is 47,000 miles long.

• The chain runs down the middle of the Atlantic Ocean, around Africa, through the Indian Ocean, between Australia and Antarctica, and north through the Pacific Ocean.

• Running along the top of the chain is a deep crack called a RIFT VALLEY. It is here that the new ocean floor is continuously created. Magma wells up from the Earth’s interior and then is cooled by the ocean, creating new crust!

Putting it All Together… • In conclusion, the Theory of Plate Tectonics is

commonly recognized and understood to be truth. The plates are slowing moving toward, away, and past each other at the boundaries of their plates.

• Next time we will learn more about the various types of plate boundaries and their names.