Mysteries of Nature 1 自然界的奥秘
There are many mysteries in nature.自然界有许多奥秘。
Mysteries are things we don't understand, such as how the Egyptian pyramids were built.神秘是我们不理解的东西，比如埃及金字塔是如何建造的。
In fact, we are surrounded by mysteries.事实上，我们被神秘所包围。
What we know about the world seems like very little.我们对这个世界所知甚少。
Scientists tell us that what we see in the universe is only a small part of what is there.科学家告诉我们，我们在宇宙中看到的只是宇宙的一小部分。
The rest is invisible, including dark matter and dark energy.其余的是看不见的，包括暗物质和暗能量
These two unknowns make up around 95% of the universe.这两个未知数约占宇宙的95%。
Evidence for their existence comes from their effects on what we can observe, such as the motion and positions of distant galaxies.它们存在的证据来自它们对我们所能观察到的东西的影响，比如遥远星系的运动和位置。
Yet, though we know very little, we are able to build airplanes and communicate with smartphones.然而，尽管我们所知甚少，但我们能够制造飞机并与智能手机通信。
In some ways we humans are very smart, or at least we think we are.在某些方面，我们人类是非常聪明的，或者至少我们认为我们是聪明的。
We still need to face big issues, like climate change, and that is going to be a huge challenge.我们仍然需要面对像气候变化这样的大问题，这将是一个巨大的挑战。
The challenge for humans will be our ability to adapt to our changing environment.人类面临的挑战将是我们适应不断变化的环境的能力。
What about other forms of life?那么其他形式的生命呢?
How do they adapt?他们如何适应?
Seasonal variations, for example, can be one of the greatest challenges for animals to overcome.例如，季节变化可能是动物要克服的最大挑战之一。
Overcoming such challenges is a great achievement, but hardly easy.克服这些挑战是一项伟大的成就，但绝非易事。
Some birds migrate thousands of kilometers each year to deal with seasonal changes.有些鸟类每年迁徙数千公里以适应季节变化。
These migrations are amazing.这些迁徙是惊人的。
Birds don't carry maps or compasses, yet they know where to go.鸟类不带地图或指南针，但它们知道去哪里。
They have developed the ability to see the Earth's magnetic field.他们已经发展了看地球磁场的能力。
This ability is a wonder of nature.这种能力是大自然的奇迹
It takes advantage of the fact that the earth is like a huge bar magnet.它利用了地球就像一个巨大的条形磁铁这一事实。
It has a north pole, which is positive, and a south pole, which is negative.北极是正的，南极是负的。
Somehow the birds are able to see this magnetic field and use it to their advantage.不知何故，鸟类能够看到这个磁场，并利用它的优势。
How do birds know where to fly? They use the Earth's magnetic field.鸟怎么知道飞到哪里去?它们利用地球磁场。
And even the way birds fly together is amazing.甚至鸟类一起飞行的方式也很神奇。
Many migrating birds fly in a V formation.许多候鸟呈V字形飞行。
They do this to conserve energy.他们这样做是为了节约能源。
In a V formation, birds can use the energy of the birds in front of them.在V形队形中，鸟类可以利用前面鸟类的能量。
This energy comes from the air currents generated by the wings.这种能量来自机翼产生的气流。
Conserving energy is necessary for the birds to survive the long journey.节约能源对鸟类在长途旅行中生存是必要的。
How do the birds know this?鸟是怎么知道的?
It's truly amazing how the birds know this.鸟类是如何知道这一点的真的很神奇。
Mysteries of Nature 2
Another amazing example of survival is the salmon.另一个令人惊奇的生存例子是鲑鱼。
Salmon spend most of their lives in the ocean, which is saltwater.鲑鱼大部分的生命都在海洋中度过，海洋是咸水。
Yet, when it's time to breed, they do so in freshwater rivers.然而，当繁殖的时候，它们会在淡水河流中繁殖。
Salmon can adapt their bodies to survive in both saltwater and freshwater.鲑鱼能使它们的身体适应在盐水和淡水中生存。
When it's breeding time, they return to the same river where they were born.到了繁殖期，它们会回到它们出生的那条河。
it seems as if they have a built-in map that guides them for hundreds of miles.他们似乎有一张内置的地图，可以指引他们走几百英里。
Where do salmon spend most of their lives? in the ocean鲑鱼一生中大部分时间在哪里度过?在海洋里
Once they leave the saltwater, they don't eat.一旦离开盐水，它们就不吃东西了。
They are determined to finish their journey, despite the many obstacles.尽管有许多障碍，他们还是决心完成他们的旅程。
They swim against strong currents, jump over waterfalls and try to escape the claws of hungry bears.它们逆流而上，跳过瀑布，试图逃脱饥饿熊的爪子。
Many die along the way, but enough of them survive to breed and produce the next generation.许多人在途中死去，但他们中有足够的鱼存活下来繁衍下一代。
Once they have laid their eggs, they die, having completed their journey.一旦它们下蛋，它们就死了，完成了它们的旅程。
It seems that their purpose in life is just to reproduce.似乎它们生活的目的就是繁衍后代。
What did they do after laying their eggs? they die它们下蛋后做了什么?他们死
Migration takes animals to new, more favorable environments when the seasons change.当季节变化时，迁徙把动物带到新的、更有利的环境中。
Some of these journeys are long and dangerous, along routes with no obvious landmarks.有些旅程漫长而危险，沿途没有明显的地标。
The longest migration is that of the arctic tern.最长的迁徙是北极燕鸥。
It flies from pole to pole, twice a year.它从一个极点飞到另一个极点，一年两次。
If a tern achieves its average lifespan of 20 years, the distance it has flown will be equivalent to a journey to the moon and back.如果燕鸥的平均寿命达到20年，那么它飞行的距离将相当于一次往返月球的旅程。
A landmark is something easy to see and remember, like a river or bay.地标是一些容易看到和记住的东西，比如河流或海湾。
Humans also migrate, but seldom if ever for seasonal variations.人类也会迁徙，但很少会因为季节的变化而迁徙。
Unfortunately, human migrations are often due to human activities.不幸的是，人类迁徙往往是由于人类活动。
Since the beginning of the 21st century, large scale migrations have become a global problem.进入21世纪以来，大规模的移民已经成为一个全球性的问题。
Millions of migrants have had to leave their countries and look for new homes.数以百万计的移民不得不离开他们的国家去寻找新的家园。
Many have died along the way or lived as refugees in camps until they are admitted into a new country.许多人在被允许进入一个新国家之前，在途中死亡或在难民营中作为难民生活。
So the question remains as to how our global community will face these challenges.因此，问题仍然是我们的全球社会将如何面对这些挑战。
Most human migrations are due to human activities.大多数人类迁徙都是由人类活动引起的。