Upheavals in the Earth
How were the mountains formed?
If we were able to slice open a mountain range such as the Rockies, the Andes or the Alps, we would see that the layers of rocks had been broken, bent and crumpled. We would also find that many of the rock layers that now tower thousands of feet above sea level were once formed at the bottom of the ocean. We know that this happened because the fossil remains of sea animals have been found in rocks on the topmost peaks.

From these facts, we conclude that the mountains were formed from the rocks of ancient sea floors - and that powerful forces from within the earth broke and folded and raised these rocks into their present positions. When the mountain ranges rose slowly out of the sea in this way, other forces began at once to go to work. Swift-flowing streams and slow-moving glaciers began tearing the mountains away. (This process of wearing away - usually, wearing away land by the action of moving water - is called erosion.) Landslides moved material from higher places to lower ones. As soon as the mountains rose above the sea, erosion began to destroy them.

Geologists believe that the surface of the earth is constantly changing in this way - that the earth's crust is in constant motion, like the waves on the surface of a sea. But instead of rising up and levelling off again in a splitsecond, as sea waves do, the movement of the "waves" of the earth's surface is measured in terms of hundreds of millions of years.
How were the mountains formed?