New theory on formation of mountains, oceans

Press, Volume CX, Issue 32460, 21 November 1970, Page 13

New theory on formation of mountains, oceans

(By

WALTER SULLIVAN)

Who has not wondered what thrust up the mountains and carved out the ocean basins? For thousands of years men have pondered these questions and the more they learned the more difficult did the answers seem to become. Thus geologists who first penetrated the mountain fastnesses of Nepal and Tibet found to their amazement that the highest mountains in the world, despite their remoteness from the sea, were formed of sedimentary rocks laid down, over a 500-million-year period, on the floor of an ocean. Those who fly across Pennsylvania and Virginia see paralied ridges, such as those of the Poconos and Blue Ridge, so machine-like in their uniformity that it is hard to believe they were not formed by intelligent action —some gargantuan bulldozer that carved those parallel furrows and ridges. Now, at last, an answer appears to be emerging—a comprehensive theory that explains how the various mountain ranges were formed, why the Pacific Ocean is rimmed with volcanoes and earthquake activity, and many other perplexing features of the earth’s surface. It has even emboldended one geology professor to predict the evolution of a mighty new mountain system along the East Coast of the United States. As new discoveries have made the theory seem increasingly plausible, there has been a race among geologists to find, in it, solutions to the major problems of their science. Evolution of the theory was initiated when geologists began to take seriously the argument that continents have drifted about on the earth and that India and Antarctica, now separated by a quarter of the globe’s circumference, were once joined. Crust divided If that were so, and India then drifted across the oceans to collide with Asia, it could have scooped up the ocean sediments that now form the Himalayas. Indeed the folds that extend from those mountains around into Burma look, on a relief map, strikingly like bedding that'

has been pushed and rumpled. However, it has been the discovery that the crust of the earth is divided into giant, movable plates, some forming continents and some forming ocean floors, that has cleared the way for a more complete and plausible theory. It has been shown that such plates are moving away from midocean rifts, such as that which bisects the Atlantic. Some oceanic plates are burrowing under a continent, as along the Pacific coast of South America, causing earthquakes and volcanic eruptions. These plate motions appar-. ently are enough to carry an entire continent to new geographical locations. Recently two scientists with the Environmental Science Services Administration published a series of maps showing how such forces tore apart an ancient continent, Pangaea, and transported its various parts to become today’s continents. The two scientists are Dr Robert S. Dietz and John C. Holden. Rock formations All of this took place within the last 200 million years, but two other geologists have reconstructed movements that they believe go back at least a billion years. They are Dr John M. Bird of the State University of New York at Albany and Dr. John F. Dewey of Cambridge University in England. In the Journal of Geophysical Research they have published an analysis of what may occur when two continents drift into one another, or when an advancing ocean floor burrows under a continent, or when such an advancing floor slips under other plates of oceanic material. They have proposed how such processes generated the many rock formations and minerals characteristic of coastal mountains. In a parallel article, published by the Geological Society of America, they have reconstructed how the crushing of an ocean that antedated the Atlantic produced the Appalachians in a succession of mountain-building events. In fact Dr Bird believes that the Atlantic Ocean has been opening and closing in a cyclic manner for more than a billion years. The last time that it closed, some 350 million years ago, the compression, in Dr

Bird’s view, formed a continuous system of mountains that extended from Scandinavia, through the British Isles, Greenland, Canada, the eastern United States, as far as Venezuela. Today the remnants of these mountains are remote from one another because of the reopening of the Atlantic. It was when Europe and Africa again broke away from the Americas, between 150 and 200 million years ago, that the final stage of Appalachian formation took place. Dr Bird’s prediction that a great new mountain range will arise along the East Coast of the United States is based on his expectation that the Atlantic will close again. The ocean floor would then again be driven under the East Coast, much as th* Pacific floor is penetrating under Chile and Peru. While this may occur “soon” on a geologic time scale, producing volcanic eruptions and earthquakes, it should not alarm residents of that region. "Soon,” in this case, does not mean tomorrow but, more likely, a million years hence.—Copyright. “New York Times” news service.