重点词汇学习
a variety of 美[ə vəˈraɪəti əv] 种种、形形色色
extinct 美[ɪkˈstɪŋkt] 不再存在的、灭绝的、绝种的
volcanic 美[vɑːlˈkænɪk]火山的 ； eruption 美[ɪ'rʌpʃ(ə)n] 喷发、长出、发疹
Life&conditions1
There are many forms of life on Earth, including human beings.
Life exists in a variety of conditions.
Some forms of life live in a watery environment, like the oceans.
Other forms of life can be found in very dry areas like deserts.
However, for any form of life to exist, conditions must be right.
When conditions are not right, that form of life will become extinct.
To become extinct means to die out completely.
Conditions must be right for life to exist.
Millions of years ago, there were forms of life that no longer exist.
When conditions changed, these forms of life died out.
One extinction event happened about 250 million years ago.
This was the largest extinction event of all time.
Many forms of life became extinct.
96% of all life in the oceans died out.
Most insects（昆虫） also became extinct.
This event happened over a period of several million years.
The causes of this extinction event are still unknown.
Possible causes include large volcanic eruptions and global warming.
Some scientists believe that there were several causes.
They believe that a series of events caused the extinctions.
Scientists are working to better understand what really happened.
Life&conditions2
In modern times, we humans face changing conditions.
For humans to live, we need clean air and clean water.
Pollution is now a growing problem around the world.
Pollution poisons the air and water that we depend on.
Polluted air makes people sick and afraid（害怕、担心） to go outside.
Polluted water poisons（毒药、毒害） our food supply（供给）.
As a result, we never know which foods are safe to eat.
Human beings can not live in a poisoned environment.
Therefore, pollution is amajor threat to our existence.
Humans need temperature to be in a comfortable range.
To be in a comfortable range means to be neither too hot nor too cold.
With global warming, global temperatures are rising.
As temperatures rise, the polar icecaps（冰盖） will melt.
As the polar icecaps melt, ocean levels will rise.
Areas of some countries will soon be under water.
People would be forced to relocate（搬迁、迁移） from flooded areas.
In nature, even small changes can sometimes have large effects.
It’s difficult to predict what’s going to happen.
The entire ecosystem that we depend on is changing.
Some of these changings are irreversible.
Irreversible changes cannot be undone（because they cannot be reversed)
(irreversible 美[ˌɪrɪˈvɜːrsəbl]无法复原(或挽回)的;不能倒转的;)
Let’s hope the humans are smart enough to understand how
the world is changing.
With more understanding, we make better choices about what to do.
We can face the challenges of the pollutionand global warming.
We need to do this before it’s too late.
This planet earth is our only home and we need to protect it.