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The earth is 4.6 billion years old.
地球有46億年的歷史了。
We humans have lived on earth for only 35 000 years, but during this period we have changed our planet a lot in many ways.
人類只在地球上存在了3.5萬年，但是在這段時間內，我們從很多方面改變了地球。
Some things we've done are very good for the earth while others are bad.
我們做的有些事對地球很有好處，有些事卻對地球有害。
All over the world, people have cut down millions of trees.
全世界的人們砍伐了無數棵樹木。
When it rains or when the wind blows, the earth is taken away.
刮風下雨時，地面的土壤都會被帶走。
Forests have become deserts, so many kinds of animals and plants are disappearing.
森林變成了沙漠，很多動物和植物都在消失。
In big cities, cars and buses have polluted the air.
在一些大城市，轎車和汽車都在污染空氣。
Now many people in cities have health problems.
現在城市里的很多人都有健康問題。
Factories have also polluted the land and the water.
工廠污染了土地和水源。
As a result, many rivers and lakes are now dead.
因此，很多河流和湖泊現在都沒有了生氣。
Around the earth, there's a special kind of oxygen call "ozone"(O3).
地球周圍有一種很特別的氧，名為“臭氧”（O3）。
It is important to the earth.
它對地球很重要。
But now air pollution is destroying it and making a very big hole in the ozone layer.
但是現在空氣污染正在破壞它，并且使臭氧層出現了空洞。
Too much harmful radiation from the sun passes through the hole and reaches the earth directly.
很多來自太陽的有害輻射都透過臭氧層空洞直抵地球。
This is very dangerous because this kind of radiation can cause cancer.
這很危險，因為這種輻射會致癌。
Carbon dioxide (CO2) in the air has increased a lot.
空氣中的二氧化碳（CO2）增加了很多。
It mainly comes from burning oil, coal and wood.
這主要是因為燃燒石油、煤和木頭。
This has formed a "blanket" around the earth.
這使得地球周圍出現了一個“地毯”。
The heat from the sun can't escape so the temperature is rising.
來自太陽的熱量無法散發，所以溫度在上升。
This is called "the greenhouse effect".
這被稱為“溫室效應”。
It causes the level of the oceans to rise and the climate of the earth to change.
這導致海平面上升，地球氣候發生改變。
All these problems are very serious, so we must do something now.
所有這些問題都很嚴重，所以我們必須采取行動。
