ESCI B.S2.O3.A4 Plate Motion

• Model the factors that cause tectonic plates to move (e.g., gravity, density, convection). 

When Alfred Wegener came up with his Continental Drift Hypothesis most other scientists didn't accept the theory because it had no way of explaining how the continents moved. It wasn't until the discovery of a liquid mantle and mid-ocean ridges that scientists had a mechanism that could explain movement. The inner Earth is still hot from the heat of formation. It continues to heat because as radioactive material decays it heats the core. This heating causes convection currents in the mantle. But convection currents are not the only thing moving the tectonic plates. As plates are created by upwelling magma at the mid-ocean ridge coll they become more dense. Plates that are farther away from the ridge are cooler and more dense. This causes the plate to sink. The sinking dense part of the plate drags the plate down with it. This is known as "slab pull".

See the process animated in this video: 

ESCI B.S2.O2.A4 Plate Tectonics Explained VID Links to an external site.

Your Assignment:  Answer the following questions in the text box:

• How does slab pull and sea-floor spreading work together to move tectonic plates?
• Explain how each of the 3 factors affects plate movement:
• Gravity
• Density
• Convection