Level5-Unit3-Part4-Listening

There are several fundamental forces that hold our universe together. One of these ,of course, is gravity , the force between objects that have mass. Another important force is the electromagnetic force. The electromagnetic force is responsible for chemical reactions. Without it, there would be no atoms or molecules. Up until a couple of hundred years ago, very little was known about this force. Learning about the electromagnetic force and how to use it was a major step forward. It revolutionized communication, transportaion and manufacturing. Imagine what life would be like without electricity!

有些主要的力将我们万物聚集在一起。当然，其中一种力叫重力，这种力存在大量物体之间。另一个重要的力电磁力。电磁力在化学反应中承担责任。没有电磁力，就没有分子或者原子。直到几百年前，对这种力量知之甚少。如今，学习并使用电磁力向前迈出了重要的一步，使通信、搬运、制造业产生彻底变革。想象一下没有电的生活是什么样子。

The electromagnetic force has two parts, the electrial force and the magnetic force. The electric force is the force between electrically charged particals, such as electrons and protons. Electric charges attract or repel each other with a force that depends on the distance between them. The magnetic force is the force between magnetic poles, such as the north and south pole. In fact, the earth is like a large bar magnet, with a north and a south pole. Many animals use the Earth's magnetic field to navigate during their migrations. We can also see this magnetic field when we use a compass.

电磁力分为两部分，分为电力和磁力。电力产生与带电粒子之间，例如：电子和质子。带电粒子之间相互吸引或者排斥，取决于它们之间相隔的距离。磁力产生于磁极之间，比如：南极和北极。事实上，地球就是一个巨大的磁球，有一个南极和北极。很多动物在迁移时利用地球的磁极来辨别方向。当我们用罗盘时，我们也用到磁力。

Why does the Earth have a magnetic field? Many scientists believe that the Earth's magnetic field is duo to the Earth's rotation. Deep inside the Earth is a solid iron core, surrounded by a liquid metal outer core.The moving electric currents inside this liquid metal create a magnetic field.

为什么地球有磁场？许多科学家认为地球的磁场与地球的自转是双重的。在地球的深处是一个固体铁芯，周围是一个液态金属外核。这种液态金属内部的移动电流会产生一个磁场。

The Earth's magnetic field is important because it protects us from the solar wind. The solar wind is a current of charged  particles coming at us from the Sun. When the solar wind nears the Earth, the Earth's magnetic field deflects it away. This protects the Earth from the radiation, which can be dangerous to life. It also protects the satellites that we use for communication.

地球磁场是重要的，因为它保护我们免受太阳风的侵袭。太阳风是来自太阳的带电粒子的电流。当太阳风接近地球时，地球的磁场使它偏离。这就保护了地球免受辐射，这对生命是危险的。它还保护我们使用的卫星进行通信。

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 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即将逆转。这叫做磁场反转。每200000到300000年。地球的磁极转换位置。这在地球的历史上已经发生过很多次，但最近这种情况一直在发生。

Recent research provides evidence that there been fi ve 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.

最近的研究提供了证据表明，在过去的500000年里发生了磁反转现象。最新的事件发生在大约41000年前。最近的研究发现，地球磁场每十年减弱约5%。按照目前的速度，下一个逆转可能发生在下个世纪。

Some people worry about the effects of a magnetic field reversal. They think there is a passibility 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 caner, 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。他们认为这种现象有可能造成许多问题。例如，在没有磁场的情况下，通信可能中断。鸟类和其他形式的生命可能会变得困惑和迷茫。另一个影响是某些形式的癌症，尤其是皮肤癌的增加。这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 reversal have caused extinctions. Humans have been on Earth for million 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 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!

场反转将是灭绝事件的可能性非常低。很少有历史证据表明先前的逆转导致了灭绝。人类在地球上已经存在了数百万年，在此期间出现了许多逆转。因此，科学家认为任何改变都是暂时的。另一个理论是，地球的外层可以围绕构成地球大部分的液态金属核心旋转。因此，在下一个逆转中，大陆可以从北向南移动位置。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 underline the importance of getting reliable imformation, backed by strong evidence.

有这么多理论，我们怎么才能知道该相信什么呢？这是很重要的，因为一些事件要求我们提前行动。否则，阻止灾难的发生已经为时已晚。这强调了获得可靠信息的重要性，有强有力的证据支持。