Earth is an ocean planet.About three bilion years ago,life on our planet began in the deep blue seas.Ninety-nine percent of the livingspace on earth is in the oceans.So water is very important for us.The water is being widely used for electricity
agriculture,home use,industry,transport,entertain---ment,and so on.But the majority of people have not realized this problem.Since changes in salinity and temperature affect Water's density,the water in the ocean is always moving.Dense water sinks and less dense water is pushed to the surface,This circulation adds energy to the marine ecosystems and moves nutrients around.Isn't it amazing that a single substance can be so important to out planet and even the whole universe?Water,which seems so simple and common, is what makes life possible. Of all the resources on earth--oils,gas,gold and so on--nothing is as precious as a drop of rain.Learning about the properties of water helps us understand life on our planet. The most important thing we can learn about water, however,is that protect it and use it wisely.Our future depends on it.
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