英语听力：自然百科 地球力场 Earth's Force Field—15

 By analyzing¹ thousands of lava² samples, geophysicists discover/ that the Earth's magnetic field has reversed over 18,000 times in the last 20 million years. On either side of these reversals is a long period of dramatically reduced field strength. 

 

 

 

During this process of reversal, the magnetic field drops very significantly and intensively. And it's happened many, many, many times rather in Earth history, / you know, they're 4.5 billion years old, and I'm saying it happens every a few hundred or thousand years or so. 

 

 

 

 

 

Years of research revealed that the last reversal occurred 780,000 years ago. 

 

 

 

It's easy to understand why there is such an interest and the possibility of a magnetic reversal. The last magnetic reversal occurred more than three quarters of a million years ago, and so in a real sense well overdue³ for another, and so the question is not if another reversal will occur, but when. 

 

 

 

Many scientists now believe that the South Atlantic Anomaly is the start of a global magnetic field reversal, the decay of our magnetic field will accelerate with serious consequences for life. 

 

 

 

Kind of radiation we are talking about is known to damage DNA⁴ and RNA and cell's structure, and it is a serious cause of cancer incidents. 

 

 

 

On Earth, magnetic field reversals are comparatively rare and erratic⁵, but on our nearest star, they occur far more frequently. 

 

 

 

Every 11 years, the direction of the Sun's magnetic field flips⁶. So the Sun's magnetic field isolates⁷ regularly, whereas the Earth has these long periods, whereas the E.U. magnetic field's direction remains⁸ more or less constant and then it flips suddenly. 

 

 

 

Although the Sun's magnetic field isn't generated in exactly the same way as the Earth, scientists still observe it closely. 

 

 

 

So you get these very different dynamos operating under the same laws of physics under glow of different environments, so by studying both of them and comparing them, we learn more about both possibilities

1 analyzing   

v.分析；分析( analyze的现在分词 )；分解；解释；对…进行心理分析n.分析

参考例句：

• Analyzing the date of some socialist countries presents even greater problem s. 分析某些社会主义国家的统计数据，暴露出的问题甚至更大。 来自辞典例句
• He undoubtedly was not far off the mark in analyzing its predictions. 当然，他对其预测所作的分析倒也八九不离十。 来自辞典例句

2 lava   

n.熔岩，火山岩

参考例句：

• The lava flowed down the sides of the volcano.熔岩沿火山坡面涌流而下。
• His anger spilled out like lava.他的愤怒像火山爆发似的迸发出来。

3 overdue   

adj.过期的，到期未付的；早该有的，迟到的

参考例句：

• The plane is overdue and has been delayed by the bad weather.飞机晚点了，被坏天气耽搁了。
• The landlady is angry because the rent is overdue.女房东生气了，因为房租过期未付。

4 DNA   

(缩)deoxyribonucleic acid 脱氧核糖核酸

参考例句：

• DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
• Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。

5 erratic   

adj.古怪的，反复无常的，不稳定的

参考例句：

• The old man had always been cranky and erratic.那老头儿性情古怪,反复无常。
• The erratic fluctuation of market prices is in consequence of unstable economy.经济波动致使市场物价忽起忽落。

6 flips   

轻弹( flip的第三人称单数 )； 按（开关）； 快速翻转； 急挥

参考例句：

• Larry flips on the TV while he is on vacation in Budapest. 赖瑞在布达佩斯渡假时，打开电视收看节目。
• He flips through a book before making a decision. 他在决定买下一本书前总要先草草翻阅一下。

7 isolates   

v.使隔离( isolate的第三人称单数 )；将…剔出（以便看清和单独处理）；使（某物质、细胞等）分离；使离析

参考例句：

• The transformer isolates the transistors with regard to d-c bias voltage. 变压器可在两个晶体管之间隔离直流偏压。 来自辞典例句
• In regions with certain isolates of TRV, spraining is more prominent. 在具有TRV某些分离物的地区，坏死是比较显著的。 来自辞典例句

8 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。