The earth's crust is made of huge, thick plates which float above the molten lava, which makes up most of the earth's liquid
core. These plates are made of rock that are absolutely enormous. From 80 to 400 miles (50 to 250 km) thick. They can move
in both directions, horizontally and vertically. After long periods of time the plates can also change in size. They can
increase in size because their margins are added to, crushed together or pushed back.
The plates are moving at a very very slow rate. Estimated at 1 to 10 cm a year. However over long long periods of time ,
the changes in the locations of the plates could be tracked. Most of the earth's volcanoes and earthquakes occur at the plate
boundaries as they interact. The layers atop the plates are called the crust. There are two distinguishable types of crusts.
Oceanic crusts and Continental crusts.