Viewmaster Reels by MrViewmaster
Our Planet Earth Geology Viewmaster Science Series Complete B 678
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| B675 Geology Bookley
OCR Excerpts A PLANET OF CEASELESS CHANGE Earth as we see it today is one frame of a moving picture that has been running for billions of years, and will run for billions of years more. Wherever we are, all around us, the ages-long story of erosion, of lands rising and falling, of volcanoes erupting and glaciers forming, of rocks and minerals being created, is in the making. Within one's own life span, the changes may seem infinitesimally small, but in geology a thousand years are as a day.* The Earth is a huge book. Its pages are the rocks that lie, layer upon layer, to make up its crust. To scientists who have learned to read them, the rocks tell a fascinating story—the autobiography of our planet. This story, as revealed by the science of geology, stretches our minds, for it takes us on a journey into a million million yesterdays. The one great theme of this diary of the Earth is Change. We see change around us every day, in little ways. Tin cans rust. Road embankments cave in. Rain cuts a gully across a vacant lot. The same forces that cause these changes, given enough millions of years, can destroy a mountain range. Thanks to the patient, observant work of generations of inquisitive men who wondered about such things as erosion, fossils, earthquakes, volcanoes, and rocks, we know that the Earth has had plenty of time for such seeming miracles of change to take place. Our planet, scientists agree, is nearly five billion—or 5,000 million—years old! Knowing something about the science of geology makes the study of rocks and the viewing of natural scenery more inter- esting. As we see the mountains, plains, lakes, and other land- forms of our world, we can look at them with deeper under- standing of the forces that shaped them; and we can imagine the scenery we have missed—the landscapes of a vanished past, whose clues remain only in the rocks they left behind them. THE GRAND CANYON COUNTRY INVASION FROM SPACE In the midst of an Arizona plain lies Meteor Crater, 570 feet deep and almost a mile wide. It is the scar left by a giant meteorite that slammed into the Earth perhaps 12,000 years ago. Iron fragments of the space invader lie buried 1,500 feet beneath the crater bed. Fortunately, catastrophies of this kind are rare because the Earth's atmosphere serves as a shield, and most meteorites burn up before striking our planet. But Meteor Crater is a reminder that we are not alone as we circle the Sun. The craters that pock the face of our airless Moon are probably scars of countless collisions with Solar System "debris." BATTLEGROUND OF THE ELEMENTS This scene dramatizes the difference between the Earth and the Moon. Like the Moon, the Earth has a rocky crust; but it also has air and water, and these make life possible. Land, air, and water—these three interact. Each contains bits of the others. Clouds move across the sky; rivers transport mud and sand; rocks and soil imprison water and air. It is the unceasing warfare of water and air against land that changes the landscapes of the Earth. The sea, kept in constant motion by air movements, washes in toward the land, building sandy beaches in its calmer moments and destroying rocky cliffs in its stormy periods. The lonely rock islands, or stacks, standing off from shore in this Oregon coast scene are remnants of cliffs that once faced the sea there. FROM THE REGIONS OF INNER HEAT Many areas of the Earth, such as the Hawaiian Islands, are built entirely of lava rock (a rather unsettling thought). Hawaii, the "Big Island," is still volcanically active, and residents sometimes see a sight of terrible beauty such as this.Lava, boiling upward from fissures in the ground, rolls toward us at night — its outer surface beginning to cool and darken, its inner heart still glowing with heat. Volcanoes and geysers are evidences of a fact we often forget: Only a thin outer layer of our planet's crust is cool enough to support life! GEOLOGICAL ODDITY Near Yosemite National Park, California, is Devils Postpile National Monument. A cluster of rock columns, like the pipes of a great organ, forms a cliff face 60 feet tall. It originated 100,000 years ago when a thick flow of lava cooled, cracking into many-sided columns. Now the destructive forces of air, water, and gravity are at work. Air and water, in the form of weather, are breaking up the columns, and gravity is pulling the pieces down into a pile of debris. We call this wearing-down process erosion. EROSION, THE SCULPTOR OF ROCKS Much of the world's most picturesque scenery is caused by the destructive work of erosion. Even the slow, patient fingers of rain and frost can sculpture strange and beautiful forma- tions. These huge balanced rocks in Rhodesia, Africa, are part of a group of rounded granite boulders known as the Giant's Playground. There is nothing mystical about them; they are simply typical examples of weathered granite, which often flakes off at the edges, taking on a rounded form that sometimes is as smooth as a pebble on the beach. THE WAY OF A GLACIER High in the Austrian Alps, a river of ice—a glacier—crawls sluggishly down a mountain slope. Thus water, even in its solid form, responds to the pull of gravity by seeking lower levels. Though ice moves slowly, it is a powerful tool of erosion. It sharpens mountain peaks, gouges hollows in slopes, and grinds valleys wider, smoother, and straighter. Note the almost classical symmetry of the valley in this picture, with its curved profile of sides and bottom that re- sembles the letter U. U-shaped valleys may be shallow or deep, but wherever they occur they are the trademarks of glaciers, either modern or ancient. VALLEYS YOUNG, MATURE, AND OLD Water, running in the channels of brooks and rivers, is the supreme land-leveler. We could see dramatic proof of this if it were possible for a movie camera to take pictures of the same river valley from the same location for several million years, and if we could view the film speeded up so that a mil- lion years was compressed into a minute. Beginning with a steep-walled, narrow gorge such as Ausable Chasm in upstate New York, we would see a valley progress through three stages which geologists call young, mature, and old. The Ausable River has cut a "young" valley through an- cient sandstone. Our imaginary movie would show the valley ETC ETC |
