Plate Tectonics is a theory explaining the structure of the earth’s crust and many associated phenomena as resulting from the interaction of rigid plates which move slowly over the underlying mantle.

Look at the pictures earth’s interior (in resources) to get an idea of how the Earth looks like from the inside. And then try to answer the following questions:

Are the layers of the same thickness?
Which layer is the hottest?
On which layer do we live?

The Earth is composed of four different layers. Many geologists believe that as the Earth cooled the heavier, denser materials sank to the centre and the lighter materials rose to the top. Because of this, the crust is made of the lightest materials (rock- basalts and granites) and the core consists of heavy metals (nickel and iron).

Now watch the following video that will help you understand the characterisitics of each layer of the Earth’s structure.

The crust is continuously moving because of what are called convection currents.
Convection currents are caused by the very hot material at the deepest part of the mantle that is rising, then cooling, sinking again and then heating, rising and repeating the cycle over and over.
When the convection currents flow in the mantle they also move the crust. The crust gets a free ride with these currents.

Watch the following video explaining convection currents in the mantle.

Due to these currents the Earth’s crust was divided into several plates called tectonic plates that glide over the mantle. These are pieces of Earth’s crust and uppermost mantle, together referred to as the lithosphere. The plates are around 100 km thick and consist of two principal types of material:
• oceanic crust (also called sima from silicon and magnesium) and
• continental crust (sial from silicon and aluminium).

Look at the map of the Major Tectonic Plates (in resources) to see where these plates meet (plate boundaries).

Plate boundaries are the most active and are the place where most earthquakes, volcanic eruptions and eruptions form.

To follow up this lesson, work out worksheet Structure of the Earth WS (in resources).
Then check your work using Structure of the Earth ANS ( in resources)