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英语听力：自然百科 地球力场 Earth's Force Field—6

时间：2014-05-26 07:04:46

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 It's clear from the fact that the Martian crust is strongly magnetized, that there must have been a magnetic field on Mars in the past, that the only way we know to magnetize rocks is for them to form in the presence of magnetic field.

 
Why did Mars lose it magnetic shield? And what effect did it have on the planet? 
 
To find / out, scientists need to analyze1 Mars' rock.
Mars Global Surveyor didn't stop to take samples but Vice2 has managed to get hold of something extremely rare, Martian meteorites4. 
We have some rocks from Mars that we're naturally transferred to Earth. These are meteorites that were blasted off from Mars by the asteroid5 common impact. 
 
Vice takes the meteorite3 sample into a special magnetically shielded chamber6. He places it in a superconducting quantum interference device or SQUID microscope for analysis. 
 
For the magnetic field, the rock is extremely weak. So, in order to do that well, we need to make these measurements in a very weak magnetic field..
 
This highly sensitive machine measures the exact strength of the rock's magnetism7. By analyzing8 different samples, Vice builds up a picture of Mars’ magnetic field at the very beginning of the planet's existence.
 
We have actually one rock from Mars that's 4.5 billion years old. And we've actually recently shown by looking the intensity9 of the magnetization record in that rock, that Mars had a magnetic field that was roughly the strength of the Earth/ today.
 
Vice's research reveals that in its first 50 million years, Mars had a strong magnetic shield. It's amazing that diversity of magnetic fields that we see about different samples. Some of them like this one: this is an ancient rock from Mars, / it's 4.5 billion years old. You will see tiny, little, isolated10 magnetic anomaly with huge areas of non- magnetic rock in between. 
 
Why Mars lost its shield is a mystery, but what happened to the planet as a result is not. When Mars lost its magnetic field, it lost its shield that’s protecting it from the solar wind, from cosmic radiation and that had consequences for the evolution of its atmosphere. The weak atmosphere allows solar wind to strip away Mars' delicate atmosphere. Its oceans vaporize, temperatures plummet11 and any primitive12 life forms die.

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1 analyze RwUzm     
vt.分析，解析 (=analyse)
参考例句：
  • We should analyze the cause and effect of this event.我们应该分析这场事变的因果。
  • The teacher tried to analyze the cause of our failure.老师设法分析我们失败的原因。
2 vice NU0zQ     
n.坏事；恶习；[pl.]台钳，老虎钳；adj.副的
参考例句：
  • He guarded himself against vice.他避免染上坏习惯。
  • They are sunk in the depth of vice.他们堕入了罪恶的深渊。
3 meteorite 2wNy1     
n.陨石；流星
参考例句：
  • The meteorite in Jilin Exhibition Hall is believed to be the largest in the world.吉林展览馆的陨石被认为是世界上最大的。
  • The famous Murchison meteorite smashed into the Australian ground in 1969.1969年著名的默奇森陨石轰然坠落在澳大利亚。
4 meteorites 12efd1ed528a28fe1f7cb667a7fbc1e0     
n.陨星( meteorite的名词复数 )
参考例句：
  • Small meteorites have left impact craters all over the planet's surface. 这个行星的表面布满了小块陨石留下的撞击坑。 来自《简明英汉词典》
  • One theory about the existence of extraterrestrial life rests on the presence of carbon compounds in meteorites. 地球外存在生命的理论是基于陨星上存在碳化合物质这一事实的。 来自《简明英汉词典》
5 asteroid uo1yD     
n.小行星；海盘车(动物)
参考例句：
  • Astronomers have yet to witness an asteroid impact with another planet.天文学家还没有目击过小行星撞击其它行星。
  • It's very unlikely that an asteroid will crash into Earth but the danger exists.小行星撞地球的可能性很小，但这样的危险还是存在的。
6 chamber wnky9     
n.房间，寝室；会议厅；议院；会所
参考例句：
  • For many,the dentist's surgery remains a torture chamber.对许多人来说，牙医的治疗室一直是间受刑室。
  • The chamber was ablaze with light.会议厅里灯火辉煌。
7 magnetism zkxyW     
n.磁性，吸引力，磁学
参考例句：
  • We know about magnetism by the way magnets act.我们通过磁铁的作用知道磁性是怎么一回事。
  • His success showed his magnetism of courage and devotion.他的成功表现了他的胆量和热诚的魅力。
8 analyzing be408cc8d92ec310bb6260bc127c162b     
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
9 intensity 45Ixd     
n.强烈，剧烈；强度；烈度
参考例句：
  • I didn't realize the intensity of people's feelings on this issue.我没有意识到这一问题能引起群情激奋。
  • The strike is growing in intensity.罢工日益加剧。
10 isolated bqmzTd     
adj.与世隔绝的
参考例句：
  • His bad behaviour was just an isolated incident. 他的不良行为只是个别事件。
  • Patients with the disease should be isolated. 这种病的患者应予以隔离。
11 plummet s2izN     
vi.(价格、水平等)骤然下跌；n.铅坠；重压物
参考例句：
  • Mengniu and Yili have seen their shares plummet since the incident broke.自事件发生以来，蒙牛和伊利的股票大幅下跌。
  • Even if rice prices were to plummet,other brakes on poverty alleviation remain.就算大米价格下跌，其它阻止导致贫困的因素仍然存在。
12 primitive vSwz0     
adj.原始的；简单的；n.原(始)人，原始事物
参考例句：
  • It is a primitive instinct to flee a place of danger.逃离危险的地方是一种原始本能。
  • His book describes the march of the civilization of a primitive society.他的著作描述了一个原始社会的开化过程。

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