Face Of The Earth (1953)

[music] [bell] Millions and millions of years ago, from a cloud of cosmic dust, a fiery Earth was born. The face of the Earth changes because of a conflict between two groups of geologic forces. The first group, like the waves crashing on the land, attack the Earth from the outside. Little by little, they wear the Earth down. Because it takes a long time for these wearing down forces to change the Earth, we cannot always see them doing it. Nevertheless, they are at work everywhere. In polar regions and in the highest mountains, glaciers form. And underneath the slow-moving tongues of glacial ice, a great force is at work, breaking up the rocks, gouging and scarring the face of the Earth. In the deserts, the sun's heat is at work, baking the rocks and drying [music] out the mud flats. In dust storms, the force of winds is at work, sweeping up and shifting the dry topsoil and sand. Rocks, split by freezing water and growing roots, roll down by the force of gravity. With the rain, running water goes to work, washing away the land. Of all the wearing down forces, running water is the most important. The force of running water in streams slowly gnaws away the rocks, cuts into the face of the Earth, and carves out gullies. In thousands of years, it may deepen and widen these gullies into huge, steep-walled canyons. [music] If there were only these wearing down forces at work, long before now, the land would have been worn away completely and covered [music] entirely with water. But there is a group of building up forces also at work. They draw their energy from [music] deep inside the Earth, and they are slowly building the land up from within. They even [music] raise land out of the sea. The highest mountain ranges now stand where [music] once there were shallow seas. We know this is true because when we dig into some of the rock layers, we find seashell fossils buried there. Sometimes these building up forces break the rock layers and push them out of line. And sometimes the pressure from these building up forces squeezes the layers into great up and down folds. [music] Many minerals, formed in hidden crevices down inside the Earth, are raised from the depths by the building up forces. [music] Pyrite, barite, [music] cuprite, [music] neptunite, dioptase, agates, [music] malachite, [music] and many others. Volcanic explosions build up the Earth in another way. They blast holes through weak places in the crust and pour out hot lava. This lava eventually cools, hardens, and becomes new land. At such volcanic explosions, geologists have an opportunity to examine directly some of the forces at work inside the Earth. Just as we cannot see this waterfall actually cutting into the rock, so we cannot always see the conflict [music] between the building up and the wearing down forces. The conflict, however, is going on all the time. Let's see some of the results of this conflict. Here, in the Painted Desert, while the building up forces within the Earth were slowly raising the land up, the force of running water was wearing it down and fashioning the hills. We can see the forms cut by rain and streams. [music] [music] In the Petrified Forest, the wearing down forces have uncovered [music] giant trees that were buried for a long time under the Earth. While they were buried, the trees were changed to rock by the work of underground water rich in minerals. The high plateaus and deep canyons of the [music] southwestern United States are in a region that was raised many times over millions of years by the building up forces. In Grand Canyon, the force of down-cutting streams has carved a trench 10 miles across and 1 mile deep into the face of the Earth, and has laid bare some of the oldest rocks in North America. In Zion Canyon, the wearing down forces have cut through these ancient sand dunes that are piled one on top of another. After desert winds had heaped up and buried the loose grains, mineral cement changed the sand into hard layers of sandstone. [music] In Bryce Canyon, younger rocks are being worn away by [music] rain and wind. Because of their weakness, they take on these strange up and down shapes. [bell] Though Bryce Canyon looks quiet and still, here, as everywhere, the struggle is going on between the building up forces and the wearing down forces. In this conflict, lies the story of the Earth's changing face. [music]