英语听力：自然百科 地球力场 Earth's Force Field—7

 The loss of the magnetic field has a catastrophic impact on the planet's evolution. Mars becomes the red planet we see today. If earth’s magnetic protection continues to fade, would it suffer the same fate? If it vanishes completely, the planet might end up like Mars.

 

 

 

 

 

How have Earth and Mars evolved differently such that Earth still has a field and Mars doesn't. Actually the problem at the moment is more one of explaining where the energy is coming from, that powers / the Earth's magnetic field. 

 

 

 

To find out exactly how and where our magnetic field is generated, scientists need to explore the Earth's interior, but this isn't easy. 

 

 

 

We really don't know a lot of detail about what's happening 2000 miles down because there is no way to send a probe there. 

 

 

 

Since there is no way to probe it directly, scientists study the structure of our planet using one of nature's most powerful phenomena¹, earthquakes. 

 

 

 

So, seismologists, they wait for an earthquake, as we say in Japan. And then they put an array of detectors² on the other side of the Earth, look at the sound going through the Earth, and by listening carefully, they can construct a map of what's inside the Earth.

 

 

 

 

 

Scientists measure earthquake vibrations³ called seismic⁴ waves. These waves don't travel through the planet in a straight line. Instead, they bend, changing speed and direction from they pass through different materials. By measuring these waves carefully, scientists learn/ that the Earth must be made up of distinct layers, like an onion. 

 

 

 

 

 

The surface layer, the crust, is made of solid rock just a few miles thick. Below sits the mantle⁵, it consists of denser⁶ semi-liquid rock. Eighteen hundred miles down is the liquid outer core, a churning sea of molten iron and nickel. It surrounds the inner core, a solid iron sphere around the size of our moon, but it's hot as the surface of the sun. Scientists believe that the magnetic iron core generates our magnetic field, but how?

1 phenomena   

n.现象

参考例句：

• Ade couldn't relate the phenomena with any theory he knew.艾德无法用他所知道的任何理论来解释这种现象。
• The object of these experiments was to find the connection,if any,between the two phenomena.这些实验的目的就是探索这两种现象之间的联系，如果存在着任何联系的话。

2 detectors   

探测器( detector的名词复数 )

参考例句：

• The report advocated that all buildings be fitted with smoke detectors. 报告主张所有的建筑物都应安装烟火探测器。
• This is heady wine for experimenters using these neutrino detectors. 对于使用中微子探测器的实验工作者，这是令人兴奋的美酒。 来自英汉非文学 - 科技

3 vibrations   

n.摆动( vibration的名词复数 )；震动；感受；（偏离平衡位置的）一次性往复振动

参考例句：

• We could feel the vibrations from the trucks passing outside. 我们可以感到外面卡车经过时的颤动。
• I am drawn to that girl; I get good vibrations from her. 我被那女孩吸引住了，她使我产生良好的感觉。 来自《简明英汉词典》

4 seismic   

a.地震的，地震强度的

参考例句：

• Earthquakes produce two types of seismic waves.地震产生两种地震波。
• The latest seismic activity was also felt in northern Kenya.肯尼亚北部也感觉到了最近的地震活动。

5 mantle   

n.斗篷，覆罩之物，罩子；v.罩住，覆盖，脸红

参考例句：

• The earth had donned her mantle of brightest green.大地披上了苍翠欲滴的绿色斗篷。
• The mountain was covered with a mantle of snow.山上覆盖着一层雪。

6 denser   

adj. 不易看透的, 密集的, 浓厚的, 愚钝的

参考例句：

• The denser population necessitates closer consolidation both for internal and external action. 住得日益稠密的居民，对内和对外都不得不更紧密地团结起来。 来自英汉非文学 - 家庭、私有制和国家的起源
• As Tito entered the neighbourhood of San Martino, he found the throng rather denser. 蒂托走近圣马丁教堂附近一带时，发现人群相当密集。