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The climate of earth has fluctuated quite a bit over the last 4.6 billion years of our planet’s history and it can be expected that the climate will continue to change. One of the most intriguing questions in earth science is whether the periods of ice ages are over or arc we living in an "interglacial" period of time between ice ages The geologic time period we are now living in is known as the Holocene (全新世). This epoch began about 11,000 years ago which was the end of the last glacial period and the end of the Pleistocene (更新世) epoch. The Pleistocene was an epoch of cool glacial and warmer interglacial periods which began about 1.8 million years ago. Since the glacial period known as the "Wisconsin" in North America and "Wrm’ in Europe when over 10 million square miles (about 27 million km2 ) of North America, Asia, and Europe were covered by ice, almost all of the ice sheets covering the land and glaciers in the mountains have retreated. Today, about ten percent of the earth’s surface is covered by ice; 96% of this ice is located in Antarctica and Greenland. Glacial ice is also present in such diverse places as Alaska, Canada, New Zealand, Asia, and California. As only 11,000 years has passed since the last Ice Age, scientists can not be certain that we are indeed living in a post- glacial Holocene epoch instead of an interglacial period of the Pleistocene and thus due for another ice age in the geologic future. Some scientists believe that an increase in global temperature, as we are now experiencing, could be a sign of an impending ice age and could actually increase the amount of ice on the earth’s surface. The cold, dry air above the Arctic and Antarctica carries little moisture and drops little snow on the regions. An increase in global temperature could increase the mount of moisture in the air and increase the amount of snowfall. After years of more snowfall than melting, the Polar Regions could accumulate more ice. An accumulation of ice would lead to a lowering of the level of the oceans and there would be further, unanticipated changes in the global climate system as well. Our short history on earth and our shorter record of the climate keeps us from fully understanding the implications of global warming. Without a doubt, an increase in the earth’s temperature will have major consequences for all life on this planet. According to the passage Holocene ______.
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The climate of earth has fluctuated quite a bit over the last 4.6 billion years of our planet’s history and it can be expected that the climate will continue to change. One of the most intriguing questions in earth science is whether the periods of ice ages are over or arc we living in an "interglacial" period of time between ice ages The geologic time period we are now living in is known as the Holocene (全新世). This epoch began about 11,000 years ago which was the end of the last glacial period and the end of the Pleistocene (更新世) epoch. The Pleistocene was an epoch of cool glacial and warmer interglacial periods which began about 1.8 million years ago. Since the glacial period known as the "Wisconsin" in North America and "Wrm’ in Europe when over 10 million square miles (about 27 million km2 ) of North America, Asia, and Europe were covered by ice, almost all of the ice sheets covering the land and glaciers in the mountains have retreated. Today, about ten percent of the earth’s surface is covered by ice; 96% of this ice is located in Antarctica and Greenland. Glacial ice is also present in such diverse places as Alaska, Canada, New Zealand, Asia, and California. As only 11,000 years has passed since the last Ice Age, scientists can not be certain that we are indeed living in a post- glacial Holocene epoch instead of an interglacial period of the Pleistocene and thus due for another ice age in the geologic future. Some scientists believe that an increase in global temperature, as we are now experiencing, could be a sign of an impending ice age and could actually increase the amount of ice on the earth’s surface. The cold, dry air above the Arctic and Antarctica carries little moisture and drops little snow on the regions. An increase in global temperature could increase the mount of moisture in the air and increase the amount of snowfall. After years of more snowfall than melting, the Polar Regions could accumulate more ice. An accumulation of ice would lead to a lowering of the level of the oceans and there would be further, unanticipated changes in the global climate system as well. Our short history on earth and our shorter record of the climate keeps us from fully understanding the implications of global warming. Without a doubt, an increase in the earth’s temperature will have major consequences for all life on this planet. What can be inferred from the passage
Throughout history, gold has been a precious material, eagerly sought and cherished. It was probably the first metal to be mined because it is beautiful and imperishable (which will always exist or cannot wear out), and because beautiful objects can be made from it-even with primitive tools. The amount of gold known to ancient peoples probably totaled not much more than the amount produced each year by the world’’s largest gold mine located in the Witwatersrand district of South Africa. Stores of gold discovered by archaeologists in Greece, Scythia, and Egypt, as well as the gold from Indian treasuries in Mexico and Peru, represented years of patient collection of small quantities from streams and veins (矿脉) , often by slave labor. The essential value of gold has always been known, even before gold was used in coinage. It remains the only universally recognized standard of value in international monetary exchange. Most of the world’’s refined gold is absorbed by governments and central banks to provide backing for paper currency. But the amount of gold used in arts and in industry is increasing. In addition to its use for jewelry, decorative finishes, and dentistry, its special properties have led to many applications in modern science and technology. Surface coatings of gold protect earth satellites from heat and corrosion, and certain electrical components and circuits of spacecraft are made of gold when extreme reliability is required. Gold was first produced in the United States from the southern Appalachian region, beginning about 1792. These deposits, though rich, were relatively small and were quickly depleted. The discovery of gold at Sutter’’s Mill in California sparked the gold rush of 1849-50. Hundreds of mining camps sprang to life as new deposits were discovered. As a result, the production of gold increased rapidly. During World War I and for some years thereafter, annual production declined to about two million ounces. When the price of gold was raised in 1934 to $35 an ounce, production increased rapidly. Shortly after the start of World WarⅡ, gold mines were closed and the government did not permit them to reopen until 1945. Since then the production of gold has not exceeded two million ounces a year. The largest producing gold mine in the United States is the Homestake Mine in South Dakota, which yields about 575,000 ounces of gold each year. Other mines scattered throughout various parts of the world produce even larger amounts of this highly prized and eagerly sought yellowish material. The author suggests that
Throughout history, gold has been a precious material, eagerly sought and cherished. It was probably the first metal to be mined because it is beautiful and imperishable (which will always exist or cannot wear out), and because beautiful objects can be made from it-even with primitive tools. The amount of gold known to ancient peoples probably totaled not much more than the amount produced each year by the world’’s largest gold mine located in the Witwatersrand district of South Africa. Stores of gold discovered by archaeologists in Greece, Scythia, and Egypt, as well as the gold from Indian treasuries in Mexico and Peru, represented years of patient collection of small quantities from streams and veins (矿脉) , often by slave labor. The essential value of gold has always been known, even before gold was used in coinage. It remains the only universally recognized standard of value in international monetary exchange. Most of the world’’s refined gold is absorbed by governments and central banks to provide backing for paper currency. But the amount of gold used in arts and in industry is increasing. In addition to its use for jewelry, decorative finishes, and dentistry, its special properties have led to many applications in modern science and technology. Surface coatings of gold protect earth satellites from heat and corrosion, and certain electrical components and circuits of spacecraft are made of gold when extreme reliability is required. Gold was first produced in the United States from the southern Appalachian region, beginning about 1792. These deposits, though rich, were relatively small and were quickly depleted. The discovery of gold at Sutter’’s Mill in California sparked the gold rush of 1849-50. Hundreds of mining camps sprang to life as new deposits were discovered. As a result, the production of gold increased rapidly. During World War I and for some years thereafter, annual production declined to about two million ounces. When the price of gold was raised in 1934 to $35 an ounce, production increased rapidly. Shortly after the start of World WarⅡ, gold mines were closed and the government did not permit them to reopen until 1945. Since then the production of gold has not exceeded two million ounces a year. The largest producing gold mine in the United States is the Homestake Mine in South Dakota, which yields about 575,000 ounces of gold each year. Other mines scattered throughout various parts of the world produce even larger amounts of this highly prized and eagerly sought yellowish material. With respect to gold, the author favors the statement that
Scholars and students have always been great travelers. The official ease for "academic mobility" is now often stated in impressive terms as a fundamental necessity for economic and social progress in the world, and debated in the corridors of Europe; but it is certainly nothing new. Serious students were always ready to go abroad in search of the most stimulating teachers and the most famous academies; in search of the purest philosophy, the most effective medicine, the likeliest mud to gold. Mobility of this Kind meant also mobility of ideas, their transference across frontiers, and their simultaneous impact upon many groups of people. The point of learning is to share it, whether with students or with colleagues. One presumes that only eccentrics have no interest in being credited with a startling discovery, or a new technique. It must also have been reassuring to know that other people is other parts of the world were about to make the same discovery or were thinking along the same lines, and that one was not quite alone, confronted by inquisition, ridicule or neglect. In the twentieth century, and particularly in the last 20 years, the old footpaths of the wandering scholars have become vast highways. The vehicle which has made this possible has of course been the aeroplane, making contact between scholars even in the most distant places immediately feasible, and providing for the very rapid transmission of knowledge. Apart from the vehicle itself, it is fairly easy to identify the main factors which have brought about the recent explosion in academic movement. Some of these are purely quantitative and require no further mention: there are far more centers of learning, and a far greater number of scholars and students. In addition one must recognize the very considerable multiplication of disciplines, particularly in the sciences, which by widening the total area of advanced studies has produced an enormous number of specialists whose particular interests are precisely defined. These people would work in some isolation if they were not able to keep in touch with similar isolated groups in other countries. Frequently these specializations lay in areas where very rapid developments are taking place, and also where the research needed for developments is extremely costly and takes a long time. It is precisely in these areas that the advantages of collaboration and sharing of expertise appear most evident. Associated with this is the growth of specialist periodicals, which enable scholars to become aware of what is happening in different centers of research and to meet each other in conferences and symposia(座谈会). From these meetings come the personal relationships which are at the bottom of almost all formalized schemas of cooperation, and provide them with their most satisfactory stimulus. According to the passage, scholars and students are great travelers because ______.
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