Unlike every other planet in the solar system, Earth's surface is 70% liquid water, which while useful for life, is strange because everything we know about how and when our planet formed says Earth should be bone dry. Watch and learn...

During the Middle Ages miners began to notice that the deeper they dug into the Earth's surface the warmer it became. The physicist Kelvin came up with a theory that the Earth's started off hot and has been cooling down ever since....