The ocean is, on the average, nearly three miles deep. The continents barely stick out above sea level. The rocks that make up the continents are lighter than the rocks of the sea floor. But those lighter rocks are still much heavier than the water of the sea. If there were nothing keeping those continental rocks gathered up into piles three miles high, they would be spread all over the sea floor. The planet earth would be completely covered with water with no land sticking out above water. What keeps those rocks piled up into continents? Origin of the Continents proposes an answer to that long standing puzzle. There is a cycle, a phenomenon that gathers one kind of rocks into continents and spread another kind of rocks out over the sea floor. This phenomenon is called the "Lithologic Cycle."