| ExosphereEarth is not alone in the universe! Even though the objects out 
              there are a long ways away, they still affect us. The Sun is 93 
              million miles away, but it still provides the light plants need 
              in order to grow. The Sun also provides the heat that keep the surface 
              of Earth warm. If we didn't have heat and light from the Sun, we 
              would all quickly become part of the cryosphere. 
              Yuk! Not a pleasant thought!
 Sometimes we get visitors 
              from the exosphere such as comet dust (which makes the meteors we 
              see at night) and meteorites (which we see in museums). Very occasionally 
              we get unwelcome visitors such as asteroids and comet heads that 
              explode in the atmosphere or hit the ground and explode to make 
              huge craters and change Earth's climate. Many people think that 
              65 million years ago one of these giant impacts caused  
              the dinosaurs to become extinct.  Back 
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