Level 5 - Unit 3 - Part 4 Listening - Magnetic Field Reversal（磁场反转）

Scientists now believe that the Earth's magnetic field is about to reverse. This is called magnetic field reversal. Every 200,000 to 300,000 years, the Earth's magnetic field reverses. In other words, the North and South magnetic poles switch places. This has happened many times in Earth's history, but it has been happening more lately.
科学家们现在相信，地球的磁场将要反转，称为磁场反转。每20万至30万年，地球的磁场就会发生逆转。换句话说，北极和南极会互换位置。这在地球历史上已经发生过很多次了，但是最近发生的更多。

Recent research provides evidence that there have been five magnetic reversals during the past 500,000 years. The most recent event happened approximately 41,000 years ago. Recent studies have found that the Earth's magnetic field has weakened about 5% per decade. At its current rate, the next reversal could happen within the next century.
最近的研究有证据表明在过去的50万年中，地球经历了5次磁场反转。最近一次发生在大约41000年前。最近研究发现，地球磁场每十年减弱约5%。按照目前的速度，下一次逆转可能在下世纪发生。

Some people worry about the effects of a magnetic field reversal. They think there is a possibility that it could cause many problems. For example, without a magnetic field, communications could be disrupted. Birds and other forms of life could become confused and get lost. Another effect would be an increase in some forms of cancer, especially skin cancer. This would be because of an increase in the amount of radiation absorbed by our bodies.
有些人担心磁场反转的影响，他们认为这可能会引起很多问题。例如，如果没有磁场，通信就会中断，鸟类和其他形式的生命可能会迷失方向。另一个影响是某些癌症的增加，尤其是皮肤癌，这可能是因为我们身体吸收的辐射量增加了。

The possibility that a field reversal would be an extinction event is very low. There is very little historical evidence to show that previous reversals have caused extinctions. Humans have been on Earth for millions of years, during which there have been many reversals. Therefore, scientists believe that any changes would be temporary. Another theory is that the Earth's outer layer could rotate around the liquid metal outer core that makes up most of the earth. So in the next reversal continents could shift positions, from north to south. Imagine, if that happened, Australia would be in the northern hemisphere.
磁场反转引发灭绝事件的可能性非常低，很少有历史证据表明以前的反转导致了物种灭绝。人类已经在地球上生活了数百万年，其间有过多次逆转，因此，科学家认为任何变化都是暂时的。另一种理论是，地球的外层可以绕着构成地球主体的液态金属外核旋转。所以在下一次的反转中，大陆可能会由南至北交换位置，想象一下，如果那样的话，澳大利亚会在北半球。

With so many theories, how can we know what to believe? This is important because some events require us to act well in advance. Otherwise it will be too late to prevent a catastrophe. This underlines the importance of getting reliable information, backed by strong evidence.
理论这么多，我们应该相信哪个呢？这很重要，因为有些事件需要我们提前采取行动，否则，要阻止一场灾难就太迟了。获取有强有力证据支持的可靠信息非常重要。