我看机经里面说有这么一道题，关键词是coastal, clovis, 25000, 40000.利用搜索引擎我找到了这篇文章，目测应该就是GRE的真题啊亲爱的同学们。果断分享中。大家顶起来啊。
Recent discoveries in New World archaeology along with new scientific methods for analyzing data have led to new ideas regarding the origin of the first peoples of the Americas and their time of arrival.
The traditional theory held that the first Americans crossed the land bridge from Siberia to Alaska around 11,500 years ago and followed an "ice-free corridor" between two large Canadian ice sheets (the Laurentide and Cordilleran) to reach unglaciated lands to the south. These first inhabitants, whose archaeological sites are scattered across North and South America, were called the Clovis people, named after the town in New Mexico where their fluted spear points used for hunting mammoth were first found in 1932.
There is now convincing evidence of human habitation sites that date earlier than the Clovis culture including sites located in South America. Monte Verde, a well-studied site located along a river near southern central Chile, dates 12,500 years ago. This site contains the buried remnants of dwellings, stone tools including large bifacial projectile points, and preserved medicinal and edible plants. How did people manage to settle this far south at such an early date? A coastal migration route is now gaining more acceptance, rather than the older view of small bands moving on foot across the middle of the land bridge between Siberia and Alaska and into the continents. Emerging evidence suggests that people with boats moved along the Pacific coast into Alaska and northwestern Canada and eventually south to Peru and Chile by 12,500 years ago—and perhaps much earlier. Archaeological evidence in Australia, Melanesia, and Japan indicate boats were in use as far back as 25,000 to 40,000 years ago. Sea routes would have provided abundant food resources and easier and faster movement than land routes. Many coastal areas were unglaciated at this time, providing opportunities for landfall along the way. Several early sites along the coast of Canada, California, Peru, Ecuador, and Chile date between 10,000 and 12,000 years ago. Many potential coastal sites are now submerged, making investigation difficult.
澳大利亚、Melanesia和日本的考古表明25,000 to 40,000 years ago开始有船。
The long-held perspective that comets are pristine remnants（残留部分） from the formation of the solar system has evolved（演变发展） from the prevailing views of 30 years ago, finds planetary scientist Dr. S. Alan Stern in a paper published in the journal Nature.
"It's fair to say that a sea change has taken place," says Stern, director of the Space Studies Department in the SwRI Space Science and Engineering Division. "We used to consider comets as wholly unchanged relics that had been stored ever since the era of solar system formation in a distant, cold, timeless deep freeze called the Oort cloud. We now appreciate that a variety of processes slowly modify comets during their storage there," he says. "As a result, it's become clear that the Oort cloud and its cousin the Kuiper Belt are not such perfect deep freezes."
我们过去认为彗星是从太阳系建立时起就存储在一个distant, cold, timeless deep freeze的叫做Oort cloud中不变的残余物。我们现在认为存储时许多缓慢的过程改变了彗星，所以很明显Oort cloud和Kuiper Belt不是完美的deep freezes。
The first evolutionary process to be recognized as affecting comets during their long storage was radiation damage, followed by the discovery that sandblasting from dust grains in the interstellar medium plays an important role. Next, researchers theorized that comets in the Oort cloud are heated to scientifically significant temperatures by passing stars and supernovae, says Stern. More recently, researchers are finding that comets in the Kuiper Belt are heavily damaged by collisions.
第一个进化过程：放射损坏，在一个发现。。。之后。然后，研究者认为Oort cloud中的彗星在经过stars and supernovae时被加热。最近，研究者发现Kuiper Belt里的彗星损毁严重。
"It also now seems inevitable that most comets from the Kuiper Belt, though constructed of ancient material, cannot themselves be ancient -- instead they must be 'recently' created chips off larger Kuiper Belt Objects, formed as a result of violent impacts," says Stern. "This is truly a paradigm shift. Many of the short-period comets we see aren't even ancient!"
The classical view that comets do not evolve while they are stored far from the sun in the Oort cloud and Kuiper Belt began to change as far back as the 1970s, but the pace of discoveries about the way comets evolve picked up considerably in the 1980s and 1990s.
不变的观点可以追溯到1970s，发现彗星演变的步伐加速发生在1980 s and 1990s
As a result of these findings, astronomers now better appreciate that comets, though still the most pristine bodies known, have been modified in several important ways since their birth, says Stern.
The realization that comets evolve during their long storage in the Oort cloud and Kuiper Belt provides insight and context to more confidently evaluate the results of astronomical and space mission observations of comets. So, too, it suggests that cometary sample return missions now on the drawing board for NASA should employ relatively deep subsurface sampling if truly pristine, ancient material is to be collected.
意识到彗星演变 给更可信的评估彗星观测结果 提供了远见和背景。它也表明如果收集到更原始的彗星样本，应该用相对深的表面的样本。
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