National Geographic : 1952 Jan
Our Home-town Planet, Earth Examining the Iron-hearted Globe, Science Gains New Knowledge of Earthquakes, Volcanoes, and Earth's Birth and Future BY F. BARROWS COLTON SEEN from as far away as Mars, our native planet, Earth, would look like a bright star, a tiny island out in space, shining by light reflected from the sun. For most people this is a new way to think of Earth, as a heavenly body, a planet, so accustomed are we to seeing it only as the solid ground beneath our feet. But today everyone is growing "planet minded." Rockets already have climbed to the upper borders of the atmosphere. There is serious talk of flying to the moon. New telescopes are exploring stupendous distances out into the vast universe. Constantly it is becoming easier to see Earth in its true per spective.* So it is timely to take a new look at our old "home-town" planet, to see it for what it really is, a mighty whirling ball of rock, car rying more than two billion human passengers on a journey through the depths of space. Mysteries of Mother Earth Though man has been living upon the earth for tens of thousands of years, only recently has he begun to penetrate its inner secrets. We still know more, in some ways, about stars billions of miles away than about what is happening inside the earth, a few hundred miles beneath our feet. Our globe has been rolling around the sun for perhaps three billion years, but even today we know less about whence it came than of what may be its ultimate fate. Fascinating mysteries still remain. Was Earth condensed from one of many clouds of dust particles scattered through space when the universe was young? Or was it born as a globule of molten rock torn from the sun by a passing star? Will our globe speed on forever at 66,600 miles per hour around the life-giving sun, or will it some day break up, sharing the sus pected fate of one nameless planet? How long can man survive on this little outpost in the infinite? How long can he count on continued stores of minerals, stowed away in Earth's crust? We are just beginning to learn answers to some of these questions, and to understand the gigantic forces at work deep down in our restless globe. Scientists by the thousands today are delv ing intensively into Earth's buried secrets, spurred on not only by curiosity but even more by the pressing need to find new sup plies of oil, metals, and radioactive minerals to help keep modern civilization going. "X-ray View" of Earth's Vitals New understanding of earthquake waves gives us an "X-ray view" of Earth's interior down to its very center. As these vibrations spread out from earthquakes, some of them travel right through the globe. Reappearing on the other side, they record information about the kind and condition of the rocks they have passed through. To pick up these messages, the earthquake experts constantly "keep their ears to the ground," day and night, around the clock, at 400 stations all over the world. With a seismologist at Harvard University I watched these tremblings as they happened, "play-by-play." The shocks recorded wavy lines on a moving strip of paper that fed out like stock quotations on ticker tape (pages 120, 128). Other scientists showed me how they squeeze rocks and metals in powerful presses and super-heat them in electric furnaces to duplicate terrific pressures and temperatures several hundred miles inside the earth. Under those conditions familiar substances undergo weird, almost unbelievable, changes. Brittle hard rocks are plastic at the same time; they can flow like cold molasses. All over the world geologists are exploring between decks in our "spaceship" to learn what stores remain on hand for the long voy age ahead. Most supplies are believed ample for a long time still. Earth as Seen from the Moon For an over-all look at Earth, take a trip to the moon in imagination and look back at the planet you've left behind. Seen from that distance, averaging 239,000 miles, Earth would loom up in the sky as a whitish disk four times the diameter of the sun. It would show outlines of our continents, white cloud banks drifting across it, and perhaps flashes of sunlight reflected from seas and lakes. Circling closer on a spaceship, you would see what most of us forget, that water covers * See "Mapping the Unknown Universe," by F. Barrows Colton, NATIONAL GEOGRAPHIC MAGAZINE, September, 1950.