Listening
It is our home in the solar system.
There is no other place for us to live.
Earth isn’t just any planet, it’s a veryspecial place.
It’s special because we depend on it formany things.
Because of the importance, we need to takecare of it.
We depend on the earth, for its air, itswater, and many of its nature resources.
Nature resources, such as coal and soil,give us energy.
Other nature resources we depend on includeforests and soil.
Forests provide clean air and wood forbuilding houses.
Soil is needed to grow plant and keep themhealthy.
We need to take care of these resources,and not waste them.
The Earth is a large rotating（自转的） sphere（球体）, about 4.5 billion years old.
The equator（赤道）which divides the earth into two hemispheres（半球体）, isabout 40,000 kilometers long.
The earth’s diameter（直径）is 12,756 kilometers.
It’s radius is half of that, or 6378 km.
The radius is the distance from the earth’scenter to its surface.
Most of the earth’s surface is covered bywater.
The rest of the earth’s surface is land.
Just above the earth’s surface is theatmosphere.
The atmosphere is a layer of gases, about500 kilometers thick.
These gases include Oxygen, Nitrogen andCarbon dioxide(二氧化碳).
This mixture of the gases is the air that webreathe.
As we move above the earth’s surface, theair gets thinner.
At high altitude（高空）the air is too thin to breathe.
At the edge of the atmosphere is space.
There is no air at all in space.
Most of the earth’s water is in the oceans.
The two largest oceans are the Pacific andAtlantic Oceans.
Unfortunately, we can’t drink ocean water
This is because ocean water has too muchsalt.
Fortunately, there is also water in lakesand rivers.
This water isn’t salty, so we can drink it.
Only about 2 percent of the world’s wateris fresh water.
Without fresh drinking water we can’t live.
A person can’t live for more than a fewdays without water.
Rivers are important
Most rivers begin in mountains and end inthe oceans.
The water flows from high ground to lowground.
At first, rivers are small, and are calledcreeks and streams
As water enters the mother stream, a rivergrows.
Some rivers become very large and long.
The longest river of the world is the Nile River,in Africa.
It almost 6,500 kilometers long
As for water volume, the Amazon is thelargest river.
The volume of water flowing through it persecond is more than in any other river
Another use of rivers is for energy.
The energy of flowing water is used toproduce electricity.
This use of water supplies over 20 percentof the world’s electricity.
Rivers are also importance for agriculture.
Without water farmers cannot grow food.
And of course, rivers can be used fortransportation.
Riverboats are used to carry things toinland cities or lake.