L5 U1-4-1 Mysteries of Nature 1

There are many mysteries in nature.

Mysteries are things we don't understand, such as how the Egyptian pyramids^[1] were built.

In fact, we are surrounded by mysteries.

What we know about the world seems like very little.

Scientists tell us that what we see in the universe is only a small part of what is there.

The rest is invisible, including dark matter and dark energy.

These two unknowns make up around 95% of the universe.

Evidence for their existence comes from their effects on what we can observe, such as the motion^[2] and positions of distant galaxies^[3].

Yet, though we know very little, we are able to build airplanes and communicate with smartphones.

In some ways we humans are very smart, or at least we think we are.

We still need to face big issues^[4], like climate change, and that is going to be a huge challenge.

The challenge for humans will be our ability to adapt to our changing environment.

What about other forms of life?

How do they adapt?

Seasonal variations^[5], for example, can be one of the greatest challenges for animals to overcome.

Overcoming such challenges is a great achievement, but hardly easy.

Some birds migrate thousands of kilometers each year to deal with seasonal changes.

These migrations are amazing.

Birds don't carry maps or compasses^[6], yet they know where to go.

They have developed the ability to see the Earth's magnetic field^[7].

This ability is a wonder of nature.

It takes advantage of the fact that the Earth is like a huge bar magnet.

It has a north pole[^8], which is positive, and a south pole, which is negative.

Somehow the birds are able to see this magnetic field and use it to their advantage.

And even the way birds fly together is amazing.

Many migrating birds fly in a V formation[^9].

They do this to conserve energy.

In a V formation, birds can use the energy of the birds in front of them.

This energy comes from the air currents^[8] generated by the wings.

Conserving energy is necessary for the birds to survive the long journey.

How do the birds know this?

It's truly amazing how the birds know this.

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1. [ˈpirəmidz]
   n. 金字塔( pyramid的名词复数 )
   Egyptian pyramids 埃及金字塔 ↩

2. ['mәuʃәn] - ※ ★★★
   n. 移动, 手势, 动作, 意向, 请求, 提议
   v. 打手势 ↩

3. ['gæləksi]
   n. 星系( galaxy的名词复数 ) ↩

4. n. 议题, 问题 ↩

5. 季节变化
   [.vєәri'eiʃәn] - ※ ★★ n. 变更 ↩

6. ['kʌmpәs] - ★
   n. 指南针, 范围, 音域 ↩

7. [mæg'netik]有磁性的
   [fi:ld]领域
   磁场
   [^8][pәul] 极点
   [^9][fɒ:'meiʃәn] - ★★
   n. 形成, 构造, 编队 ↩

8. 气流
   current
   ['kʌrәnt] - ※ ★★★★★
   n. 涌流, 趋势, 流 ↩