英语听力：自然百科 地球力场 Earth's Force Field—10

 Larry Newitt from the Geological Survey of Canada charts the movement of the magnetic North Pole as it wanders the icy reaches of northern Canada. 

 

To determine where the magnetic pole / is, we can't rely on one single observation. What I try to do is surround the estimated position of the pole, taking as many observations as possible. 

 

This wandering is / symptomatic of fluctuations¹ in the geodynamo. In recent decades, scientists have noticed that the pole has been moving faster. 

 

Over much of the past a hundred years, it has been around 10 kilometers per year. But since about 1970, it started to accelerate and now it's moving along at about 40 kilometers per year.  

 

In around 50 year's time, it might twitch² Siberia. So does the wandering pole's acceleration³ have any connection with the Earth's weakening magnetic field? 

 

Professor Jeremy Bloxham is searching for an answer. He uses the records of / early sailors to chart the magnetic north movement over the past 300 years. 

 

Because of the importance of the magnetic field to navigation, people on trading ships and voyages of exploration back in the 17th century or the 18th century were making very careful systematic⁴ measurements of the magnetic field.

 

Bloxham feeds the historical data into a computer which creates an impression of the Earth's magnetic history. 

 

What we have here is an animation⁵ that would show us how the field has changed over the 300 years or also since 1690. And in the shades of red and orange, were showing the strength of the magnetic field as it comes out of the core. And in the shades of blue, the strength of the magnetic field as it goes back into the core. 

 

Over the last 150 years, scientists have measured a 10% decline in the overall strength of the Earth's magnetic field. It's fading 10 times faster and if the geodynamo suddenly stops, crucially, parts of the field are behaving differently. 

 

Now, as we get into the beginning of the twenty of century, we begin to see the emergence⁶ of this blue patch here, beneath Southern Africa which then drifts to the west and joins up with this other patch, making a large region of the core-mantle boundary with the field is going in the opposite direction from what we would expect.

1 fluctuations   

波动，涨落，起伏( fluctuation的名词复数 )

参考例句：

• He showed the price fluctuations in a statistical table. 他用统计表显示价格的波动。
• There were so many unpredictable fluctuations on the Stock Exchange. 股票市场瞬息万变。

2 twitch   

v.急拉，抽动，痉挛，抽搐；n.扯，阵痛，痉挛

参考例句：

• The smell made my dog's nose twitch.那股气味使我的狗的鼻子抽动着。
• I felt a twitch at my sleeve.我觉得有人扯了一下我的袖子。

3 acceleration   

n.加速，加速度

参考例句：

• All spacemen must be able to bear acceleration.所有太空人都应能承受加速度。
• He has also called for an acceleration of political reforms.他同时呼吁加快政治改革的步伐。

4 systematic   

adj.有系统的，有计划的，有方法的

参考例句：

• The way he works isn't very systematic.他的工作不是很有条理。
• The teacher made a systematic work of teaching.这个教师进行系统的教学工作。

5 animation   

n.活泼，兴奋，卡通片／动画片的制作

参考例句：

• They are full of animation as they talked about their childhood.当他们谈及童年的往事时都非常兴奋。
• The animation of China made a great progress.中国的卡通片制作取得很大发展。

6 emergence   

n.浮现，显现，出现，（植物）突出体

参考例句：

• The last decade saw the emergence of a dynamic economy.最近10年见证了经济增长的姿态。
• Language emerges and develops with the emergence and development of society.语言是随着社会的产生而产生，随着社会的发展而发展的。