1. The Interior of the Earth
What exactly is in there?

2. Of course we do not know for certain, but we are pretty sure the Earth’s interior is made of several distinct layers.

3. Starting from the outside, there is the relatively thin crust, the very thick mantle, and then the outer core and inner core.

4. The lithosphere includes the solid crust and the solid uppermost layer of the mantle. (The lithosphere is broken up into tectonic plates.) The asthenosphere is the semi-liquid layer of upper mantle. (The plates are believed to flow slowly on top of the asthenosphere.)

5. The mantle is thick - it makes up about 84% of the volume of the Earth
The mantle is thick - it makes up about 84% of the volume of the Earth. And it is hot - it is believed that convection currents in the mantle are what make the plates move.

6. The outer core and inner core are even hotter.

7. The outer core is liquid iron, but the inner core – even though it is hotter – is SOLID iron. Yes, solid – NOT liquid. Can you guess why?

8. The answer might surprise you.
How do you suppose scientists know so much about the interior of the Earth?
The answer might surprise you.

9. Earthquakes. Seismic waves actually
Earthquakes! Seismic waves actually. (P and S waves, to be more specific.)

10. An understanding of the interior of the Earth helps us to understand the driving force behind plate tectonics. (Click on image for a video – 5:42)