题型：阅读理解 题类：常考题 难易度：普通
上海市黄浦区2019届高三上学期英语期末考试试卷
The surface of Venus has never seemed very hospitable. Temperatures change around 470℃(900°F), the result of a runway greenhouse effect, and the pressure of its atmosphere, thick with carbon dioxide and sulfuric acid(硫酸), is some 90 times that of Earth's. Lead(铅) would flow like water on Venus, and water cannot have existed in liquid form for perhaps a billion years.
Now NASA'S Magellan spacecraft seems to have found one more horror in the nasty landscape: active volcanoes. Last week the space agency released the first detailed map of Venus and the most dramatic images ever made of its surface. The picture offer the best evidence to date that a planet once assumed dead is actually a lively pot of geological change.
The most amazing image is of Venus's second tallest mountain, Maat Mons, which rises 8km(5 miles) . Most of the planet's many peaks, including 9.5-km-(6-mile-) high Maxwell Montes, look bright in the radar pictures Magellan takes from its orbit above the permanent could cover. That means they are strong reflectors of radar waves. But Maat Mons is dark; like the Stealth bomber, it absorbs much of the radar falling on it.
This interesting fact, say project scientists, is a strong hint that the mountains has recently been covered with lava(熔岩). Rock that sits on the surface of mountaintops appears to weather quickly in the hot , chemically reactive atmosphere, creating a soil that is rich in iron sulfide(硫化铁). It is this mineral, the scientists believe, that can easily be seen on radar. If Maat Mons doesn't have any, it has probably been resurfaced, perhaps within the past few years.
Such resurfacing has undoubtedly taken place in Venus lowlands: earlier images of the planet showed vast areas that are remarkably free of craters(火山坑). That would be easy to explain on a Planet like Earth, where cratering from meteor strikes is erased by steady erosion. But while there is some evidence of wind erosion on Venus, the best explanation for the lack of cratering is periodic lava flow. Magellan has found direct evidence of such flows, including domelike upwellings and hardened streamed of rock trailing down the sides of Venusian peaks. There are also signs of other geologic activities, including dramatic faulting and several distinct incidents of mountain building. But the evidence can't indicate whether they really occurred millions of years ago. The case for active Venusian volcanoes is not yet proved, but Magellan, which is now well into its second complete survey of the planet's surface, may eventually settle the issue.
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