1. The Earth is composed of layers including a solid crust, mantle of hot rock, and an inner and outer core made of iron and nickel. 2. Earthquakes send seismic waves that are detected by seismometers around the world, allowing scientists to learn about the Earth's internal structure. 3. There are two types of seismic waves - P waves and S waves. S waves cannot pass through liquids, which provides evidence that the outer core is liquid based on waves not being detected on the opposite side of the Earth from some earthquakes.

1. MOVEMENT AND CHANGE Movements in the Earth

2. Structure of the Earth

12. Longitudinal waves (P waves)

14. Transverse waves (S waves)

22. MOVING PLATES

30. mantle explosive volcanoes powerful earthquakes crust melts