英语听力：自然百科 地球力场 Earth's Force Field—2（在线收听） |
Radiation causes damage at the most fundamental level. It mutates the blueprint of life, DNA. Earth's magnetosphere is our crucial defense. It's so fundamental to our evolution and continued existence that the race is on to understand why it's changing. Although scientists can peer millions of miles into space, they still can't see the Earth's magnetic field. NASA scientist Dr. Mario Acuna's simple demonstration helps us to visualize its basic structure. “We can use a real bar magnet to visualize what the magnetic field of the Earth may look like. So, we're gonna put this under this.
It’s a cardboard here. And now we are going to sprinkle slowly, some iron filings. In school, we all play with iron filings and we sprinkle them on a bar magnet, then we see these lines that form, that go from North to the South. And that in a fact, basically describes the rough geometry of the Earth's magnetic field.”
So, just as iron filings arrange themselves, around the north and south poles of a bar magnet, the Earth's magnetic field spurts out like a fountain at the magnetic South Pole. It encircles the entire planet and streams back down into the Earth at the magnetic North Pole.
Scientists believe it's generated 3000 miles beneath our feet, deep within the Earth's interior. From here, it throws out a vast magnetic cocoon that envelops the entire planet. This blocks out the solar wind, a constant barrage of superheated charged particles streaming from the Sun at up to a million miles per hour.
Professor Daniel Lathrop from the University of Maryland has seen how powerful the solar wind can be.
“Solar wind comes in and hits the bow shock on the magnetosphere, and tends to just go around them with whole thing shaped like a big tadpole. Most of the radiation then ends up streaming past the Earth. A little bit leaks in and hits the atmosphere near the Poles.”
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| 原文地址：http://www.tingroom.com/lesson/zrbaike/2011/259934.html |