We already know that Mars resembles the earth in many aspects:general size,presence of water,length of day,range of temperatures.These resemblances have caused many people to consider a centurieslong project:to terraform Mars.Terraforming means altering a planet’s surface so that Earth’s life forms can survive there.This concept,previously found only in science fiction is now being seriously considered by scientists.

　　Terraforming Mars is theoretically simple:add nitrogen and oxygen to the atmosphere;pump water to the surface;and add the earth’s plants and animals in the order in which they developed on Earth.But it will take at least 300 years.

　　Some people think that such a project is too huge for humans to undertake,but there are very good reasons to make the attempt.The earth now contains some 6 billion people,and no one has any idea of how many humans the earth can support.Our very existence and numbers are threatening many other species.We also have had some experience with terraforming our own planet:altering the landscape,the atmosphere and the climate.Currently terraforming earth has become a wiser activity as we try to control global warming,air and water pollution,and preserve some natural living places.

　　While the possibility of such a project is small,it is not impossible.Even if earth bound societies come and go in the next 300 years,the project can continue through the work of the Mars settlers without the need for constant backing from the earth.

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