英语听力：自然百科 地球力场 Earth's Force Field—14

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By analyzing¹ different samples of lava², Herrero / Bervera  has built up a picture of how the filed has changed since long before humans were around.

 

 

 

They are actually the recorders of the Earth's magnetic field in hundreds of years, thousands of years, and this is what we need actually to know something about the Earth's magnetic filed. 

 

 

 

 

 

Lower layers of rock take Herrero Bervera progressively further back in time. 

 

 

 

To unlock the information, he takes a sample of the ancient lava, as well / he is showing how the field strength has changed, the sample will also reveal another vital piece of information. He carefully notes the sample's exact location.

 

 

 

And we would, we're going to measure it, demand the decision of the sample we collected in the field. 

 

 

 

Back at the lab, he analyses it using a magnetometer like a pottery³, lava contains / magnetite. When it cools, particles of magnetite lining⁴ up with the Earth's magnetic field like tiny compass needles, recording⁵ both its strength and its direction. In this sample, the magnetite lines with today's magnetic north. 

 

 

 

This sample wasn't placed in the past 700,000 years when the field was actually gluttonized by a normal polarity . 

 

 

 

But in old samples, they discover something incredible. The magnetic particles point South rather than North. They date back to a time when the magnetic field polarity was the opposite of today's.

 

 

 

There was a reversal actually recorded by these lava floors. I will be actually / able to see a sequence of points that are actually defining the behavior or the evolution of the magnetic field from the one polarity to the other polarity.

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