f you were to look down on Earth from<br > outer space， as an astronaut might， the planet<br > would resemble a watery blue gem<br > Viewed from the blackness of space，<br > the orb is not divided by interna- f<br > tional boundaries into individ-<br > _4.<br > ual countries， but appears as<br > a cohesive， almost lyricall~-~<br > entity. Indeed， on the I~<br > J<br > planet itself， everything is<br > interrelated. Together，<br > the atmosphere (the k.~r--<br > gases that surround the<br >planet， including those<br >that make up the air we<br >breathe)， the hydrosphere<br >(including the bodies of water<br >that cover the earth)， and the litho- ~ ~<br >sphere (the outer hard surtZace of the planet，<br >generally considered to be about 50 miles thick)<br >make fife possible on the earth. The word geogra-<br >phy， derived from the Greek words geo ("earth")<br >andgraptwin ("to write or carve")， reters to the sci-<br >entific study of Earth--its land， water， and air， and<br >the distribution of plant， animal， and human life.<br >Geographers study such interrelationships as<br >cfimate and vegetation， atmosphere and the sun，<br >water and soil， and human industries and the<br >