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The ocean bottom ------a region nearly 2.5 times greater than the total land area of the Earth ---- is a vast frontier that even today is largely unexplored and uncharted. Until about a century ago, the deep-ocean floor was completely inaccessible, hidden beneath waters averaging over 3,600 meters deep. Totally without light and subjected to intense pressures hundreds of times greater than at the Earth's surface, the deep-ocean bottom is a hostile environment to humans, in some ways as forbidding and remote as the void of outer space. Although researchers have taken samples of deep-ocean rocks and sediments for over a century, the first detailed global investigation of the ocean bottom did not actually start until 1968, with the beginning of the National Science Foundation's Deep Sea Drilling Project (DSDP).Using techniques first developed for the offshore oil and gas industry, the DSDP's drill ship, theGlomar Challenger, was able to maintain a steady position on the ocean's surface and drill in very deep waters, extracting samples of sediments and rock from the ocean floor. The Glomar Challenger completed 96 voyages in a 15-year research program that ended in November 1983. During this time, the vessel logged 600,000 kilometers and took almost 20,000 core samples of seabed sediments and rocks at 624 drilling sites around the world. The Glomar Challenger's core samples have allowed geologists to reconstruct what the planet looked like hundred of millions of years ago and to calculate what it will probably look like millions of years in the future. Today, largely on the strength of evidence gathered during the Glomar Challenger's voyages, nearly all earth scientists agree on the theories of plate tectonics and continental drift that explain many of the geological processes that shape the Earth. The cores of sediment drilled by the Glomar Challenger have also yielded information critical to understanding the world's past climates. Deep-ocean sediments provide a climatic record stretching back hundreds of millions of years, because they are largely isolated from the mechanical erosion and the intense chemical and biological activity that rapidly destroy much land-based evidence of past climates. This record has already provided insights into the patterns and causes of past climatic change --- information that may be used to predict future climates. 重点单词： Basic to any understanding of Canada in the 20 years
after the Second World War is the country's impressive
population growth. For every three Canadians in 1945, there
were over five in 1966. In September 1966 Canada's population
passed the 20 million mark. Most of this surging growth
came from natural increase. The depression of
the 1930's and the war had held back marriages, and the
catching-up process began after 1945. The baby boom continued
through the decade of the1950's, producing a population increase
of nearly fifteen percent in the five years from 1951 to 1956.
This rate of increase had been exceeded only once before
in Canada's history, in the decade before 1911. when the prairies
were being settled. Undoubtedly, the good economic conditions
of the 1950's supported a growth in the population, but the
expansion also derived from a trend toward
earlier marriages and an increase in the average size of families.
In 1957 the Canadian birth rate stood at 28 per thousand, one
of the highest in the world. 重点单词： Are organically grown foods the best food choices?The advantages claimed for such foods over conventionally grown and marketed food products are now being debated. Advocates of organic foods ----- a term whose meaning varies greatly --- frequently proclaim that such products are safer and more nutritious than others. The growing interest of consumers in the safety and nutritional quality of the typical North American diet is a welcome development. However, much of this interest has been sparked by sweeping claims that the food supply is unsafe or inadequate in meeting nutritional needs. Although most of these claims are not supported by scientific evidence, the preponderance of written material advancing such claims makes it difficult for the general public to separate fact from fiction. As a result, claims that eating a diet consisting entirely of organically grown foods prevents or cures disease or provides other benefits to health have become widely publicized and form the basis for folklore. Almost daily the public is besieged by claims for "no-aging"
diets, new vitamins, and other wonder foods. There
are numerous unsubstantiated reports that natural
vitamins are superior to synthetic ones, that
fertilized eggs are nutritionally superior to
unfertilized eggs, that untreated grains are better than
fumigated grains, and the like. 重点单词： There are many theories about the beginning of drama in ancient Greece. The one most widely accepted today is based on the assumption that drama evolved from ritual. The argument for this view goes as follows. In the beginning, human beings viewed the natural forces of the world, even the seasonal changes, as unpredictable, and they sought, through various means, to control these unknown and feared powers. Those measures which appeared to bring the desired results were then retained and repeated until they hardened into fixed rituals. Eventually stories arose which explained or veiled the mysteries of the rites. As time passed some rituals were abandoned, but the stories, later called myths, persisted and provided material for art and drama. Those who believe that drama evolved out of ritual also argue that those rites contained the seed of theater because music, dance, masks, and costumes were almost always used. Furthermore, a suitable site had to be provided for performances, and when the entire community did not participate, a clear division was usually made between the "acting area" and the "auditorium". In addition, there were performers, and, since considerable importance was attached to avoiding mistakes in the enactment of rites, religious leaders usually assumed that task. Wearing masks and costumes, they often impersonated other people, animals, or supernatural beings, and mimed the desired effect --- success in hunt or battle, the coming rain, the revival of the Sun --- as an actor might. Eventually such dramatic representations were separated from religious activities. Another theory traces the theater's origin from the human interest in storytelling. According to this view, tales (about the hunt, war, or other feats) are gradually elaborated, at first through the use of impersonation, action, and dialogue by a narrator and then through the assumption of each of the roles by a different person. A closely related theory traces theater to those dances that are primarily rhythmical and gymnastic or that are imitations of animal movements and sounds. 重点单词： Staggering tasks confronted the people of the United States, North and South, when the Civil War ended. About a million and a half soldiers from both sides had to be demobilized, readjusted to civilian life, and reabsorbed by the devastated economy. Civil government also had to be put back on a peacetime basis and interference from the military had to be stopped. The desperate plight of the South has eclipsed the fact that reconstruction had to be undertaken also in the North, though less spectacularly. Industries had to adjust to peacetime conditions: factories had to be retooled for civilian needs. Financial problems loomed large in both the North and the South. The national debt had shot up from a modest $65 million in 1861, the year the war started, to nearly $3 billion in 1865, the year the war ended. This was a colossal sum for those days but one that a prudent government could pay. At the same time, war taxes had to be reduced to less burdensome levels. Physical devastation caused by invading armies, chiefly in the South and border states, had to be repaired. This herculean task was ultimately completed, but with discouraging slowness. Other important questions needed answering. What would be the future of the four million Black people who were freed from slavery? On what basis were the Southern states to be brought back into the Union? What of the Southern leaders, all of whom were liable to charges of treason? One of these leaders, Jefferson Davis, president of the Southern Confederacy, was the subject of an insulting popular Northern song,"Hang Jeff Davis from a Sour Apple Tree", and even children sang it. Davis was temporarily chained in his prison cell during the early days of his two-year imprisonment. But he and the other Southern leaders were finally released, partly because it was unlikely that a jury from Virginia, a Southern Confederate state, would convict them. All the leaders were finally pardoned by President Johnson in 1868 in an effort to help reconstruction efforts proceed with as little bitterness as possible. 重点单词： |
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