科学美国人60秒:巴哈马群岛成因-托福听力下载

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　　科学美国人60秒中英文翻译：巴哈马群岛成因

　　科学美国人60秒英文文本

　　Imagine paradise.

　　Now imagine the Bahamas.

　　Hard to tell the difference.

　　The island nation boasts brilliant white sands, clear waters and vibrant coral reefs.

　　The waters of the Bahamas are so clear because they're low in nutrients.

　　They're therefore relatively free of the microscopic life that turns richer waters murky—and is normally associated with the deposition of calcium carbonate.

　　So how did the reefs come to be?

　　巴哈马群岛.jpg

　　A group of scientists argue that dust from across the Atlantic in Africa may have initiated the process.

　　Dust blows off the Sahara today, reaching all the way to the Americas.

　　Fertilized by the dust, cyanobacteria can then grow and pull carbon dioxide out of the water.

　　That activity in turn causes calcium carbonate to precipitate, an event known as a whiting.

　　And the cyanobacteria also fix nitrogen from the atmosphere, helping other microorganisms to thrive.

　　This may have been going on for a very long time.

　　Enough of such cyanobacterial work over enough time and eventually you get the Bahamas, built out of calcium carbonate.

　　At least that's what's suggested by trace elements in Bahama sediments.

　　The hypothesis is in the journal Geology.

　　Fertilizing similarly nutrient poor waters might help reduce rising levels of carbon dioxide that are causing uncomfortable global warming.

　　And maybe we'd get some pretty nice islands out of the deal—eventually.

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