The Evolution of the Universe 



17 



EVOLUTION OF THE PLANET EARTH 



The earth is almost spherical, shghtly flattened at the poles, and 

 slightly pear-shaped by virtue of the southern hemisphere being 

 a httle larger than the northern hemisphere (O'Keefe et at, 1959). 

 The surface of the earth is highly irregular, marked by high moun- 

 tain ranges, deep ocean troughs, and lesser relief features in be- 

 tween. The total relief from the deepest ocean trough to the high- 

 est mountain, however, is less than 13 miles, minute compared 

 with the approximately 4,000 mile radius of the earth as a whole 

 (Fig. 5). Almost three-fourths of the earth's surface is covered by 



Approximate area of 

 V .^ Photograph \^^' 



Fig. 5. The surface of the earth as seen from an altitude of 143.4 miles, 

 showing its irregularities. The photo shows parts of Mexico, the Gulf of 

 California, Arizona, and California to north of Los Angeles, shown in inset 

 map. The mountains near the horizon on the right include peaks ranging 

 from 5,000 to over 10,000 feet high. Photo taken from the U.S. Navy's Viking 

 12 rocket. (Official U.S. Navy Photo; inset added.) 



