【文章內(nèi)容簡介】 ow signs of having been speared. ■Perhaps the paintings were inspired by the need to increase the supply of animals. Cave art seems to have reached a peak toward the end of the Upper Paleolithic period, when the herds of game were decreasing.■Therefore, if the paintings were connected with hunting, some other explanation is needed. 翻譯：___________________________________________________________________10. Continued sedimentation—the process of deposits39。 settling on the sea bottom—buries the organic matter and subjects it to higher temperatures and pressures, which convert the organic matter to oil and gas. ■As muddy sediments are pressed together, the gas and small droplets of oil may be squeezed out of the mud and may move into sandy layers nearby. ■Over long periods of time (millions of years), accumulations of gas and oil can collect in the sandy layers. ■Both oil and gas are less dense than water, so they generally tend to rise upward through watersaturated rock and sediment.■Unless something acts to halt this migration, these natural resources will eventually reach the surface. 翻譯：________________________________________________________________________11. Scientists have known for some time that certain plants, called hyperaccumulators, can concentrate minerals at levels a hundredfold or greater than normal. ■A survey of known hyperaccumulators identified that 75 percent of them amassed nickel, cobalt, copper, zinc, manganese, lead, and cadmium are other minerals of choice.■Hyperaccumulators run the entire range of the plant world. ■They may be herbs, shrubs, or trees.■Many members of the mustard family, spurge family, legume family, and grass family are top hyperaccumulators. Many are found in tropical and subtropical areas of the metals may afford some protection against planteating insects and microbial pathogens.Certain minerals are more likely to be accumulated in large quantities than others.翻譯：______________________________________________________________________12. Speculation on the origin of these Pacific islands began as soon as outsiders encountered them。 in the absence of solid linguistic, archaeological, and biological data, many fanciful and mutually exclusive theories were devised. Pacific islanders were variously thought to have e from North America, South America, Egypt, Israel, and India, as well as Southeast Asia. ■ Many older theories implicitly deprecated the navigational abilities and overall cultural creativity of the Pacific islanders. ■ For example, British anthropologists Smith and assumed that only Egyptians would have been skilled enough to navigate and colonize the Pacific. ■They inferred that the Egyptians even crossed the Pacific to found the great civilizations of the New World (North and South America). ■ In 1947 Norwegian adventurer Thor Heyerdahl drifted on the balsalog raft westward with the winds and currents across the Pacific from South America to prove his theory that Pacific islanders were Native Americans (also called American Indians).Later theories concentrated on journeys in the other direction.翻譯：_____________________________________________________________________13. One interpretation regarding the absence of fossils during this important 100millionyear period is that early animals were soft bodied and simply did not fossilize. ■Fossilization of softbodied animals is less likely than fossilization of hardbodied animals, but it does occur. ■ Conditions that promote fossilization of softbodied animals include very rapid covering by sediments