英语听力：自然百科 地球力场 Earth's Force Field—13

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We were used to the idea that a compass points somewhere near the North Pole and hence we can use it for navigation, but there are periods in the past when the compass would have pointed² in exactly the opposite direction.

 

 

 

Glatsmire's research also suggests that there's a decline in the magnetic field strength before and after these reversals. Does this explain why the magnetic field is currently weakest beneath the South Atlantic? Are the magnetic poles about to reverse? 

 

 

 

We've never witnessed a reversal so we don't really know what would look like. We could guess and would almost surely take the bauble³ of the magnetosphere and contract/ it inward, closer to the surface of the Earth.

 

 

 

If this is the start of the magnetic field reversal, our planet will face increasing exposure to cosmic radiation for thousands of years to come. But so far, the random⁴ reversal of the Earth's magnetic field has only been seen inside a computer. For concrete evidence, scientists turn their attention to the volcanic⁵ islands of Hawaii. 

 

 

 

Locked inside this ancient lava⁶ is a pristine⁷ record of Earth's magnetic field stretching back millions of years. 

 

 

 

Professor Emilio Herrero-Bervera is searching for clues to Earth's magnetic past. 

 

 

 

One of the reasons why we are coming here is because we're looking for the lava floors that are relatively⁸ thin, you can see the boundary of this lava floor and these are all the boundaries. From here you see another one, and another one and another one, all these fantastic sequence of lava floors we're talking about 300 floors, 400 floors.

 

 

 

Molten lava from these island volcanoes accumulates over millions of years. When the lava flows hit the seawater, they cool rapidly, creating snapshots of Earth's magnetic field strength.

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