[MUSIC] JOAN CARTAN-HANSEN, HOST: There are four basic states of matter: solid, liquid, gas, and plasma.
When matter changes from one state to another, it's called a phase change.
So, what causes a phase change?
Well, there are a few different things.
One is to change the temperature.
Make it cold and water turns from a liquid into a solid.
Turn up the heat and water goes from a liquid into a gas.
Pressure can also change matter's state.
Deep in the earth, the solid rock is under a lot of pressure.
But as the rock moves toward the surface, the pressure drops and the temperature changes.
So solid rock turns into liquid magma.
On the other hand, if you take carbon dioxide gas and put it under high pressure, it turns into a solid called dry ice.
Water, by the way, is the only abundant compound on earth that regularly goes through phase shifts from solid to liquid to gas and back.
Other compounds make the shifts, but not as easily as water.
For more information about states of matter, check out the Science Trek website.
You'll find it at science trek.org