EARTH AND NATURAL HISTORY ORIENTATION 



it is aflected by various levels, or orders, of geological 

 characteristics. The first-order features are the 

 oceans and the continents; the second-order features 

 are the processes of erosion; and the third-order 

 features include the processes of mountain formation 

 and uplift. The atmosphere and ocean waters both 

 contain five main layers. Even the complexity of life 

 displays an organization, the life spectrum. 



Furthermore, order is displayed by the horizontal 

 and vertical zonation of climate and the eflfects of 

 climate as shovs^n in soil and vegetation. Climatically, 

 zonation features tropical, dry, warm-temperate, 

 cool-temperate, and arctic conditions. ' With each 

 kind of climate there is a definite association of living 

 creatures (especially plants) and soils. 



This discussion provides only a- brief glimpse into 

 the characteristic orderliness of earth and its phenom- 

 ena. However, it does indicate a general framework 

 for the more detailed consideration that will follow. 



AFFECTING FORCES 



The forces affecting us can be considered in two 

 groups: the internal and the external ones. 



Internal forces already mentioned (actually, the 

 producers of these forces) are the physical phenomena 

 that cause movements and modifications of the 

 earth's crust, the magnetic field, and the radiation 

 belts. Another internal force is gravity. Gravity, 

 which from our point of view is the attraction of all 

 objects toward the center of the earth's core, is the 

 great leveler of our planet. It also has a bearing on 

 previously considered processes. Gravitation main- 

 tains a constant strain upon all elevations. It causes 

 movable objects to proceed down slope. It maintains 

 ocean waters in a nearly spherical form that is dis- 

 turbed only by winds, which cause waves, and by the 

 gravitational attractions of sun and moon, which 

 cause the tides. 



Gravity is not merely a function of the earth's 

 mass. It is true that mass is the main force of attrac- 

 tion among objects, but mass is counteracted by the 

 earth's rotation. In fact, rotational differences affect 

 the weight of an object at different latitudes upon 

 this planet. However, this difference is only great 

 enough to increase by one pound at the poles the 

 weight of an object that is two hundred pounds at the 

 equator. 



The primary sources of external forces are the sun 

 and moon. Other planets, moons, and stars produce 

 minor effects. Already treated were the effects of 

 solar radiation and sun-moon gravitation effects. In 

 addition, solar heat reacts upon our atmosphere and 

 lithosphere to produce weathering and other types of 

 erosion. Erosion is related to a constant circulation 

 of the earth's air and water reacting with solar rays 

 and gravity. That part of the circulation that includes 

 water alone is called the hydrologu cycle (Figure 17.4, 

 p. 308). It consists of the evaporation of water from 

 the oceans into the air to be formed into clouds, the 

 precipitation of this water in the form of snow or rain, 

 and the eventual return of most of the water to the 

 ocean by runoff. 



Later, we will consider the work of air and water in 

 the reduction of landscape profiles. If the effects of 

 these factors and that of gravity were not counter- 

 acted by uplift, vulcanism, and mountain building, 

 the land would soon be entirely flat. 



SELECTED READINGS 



Gamow, George, 1948. Biography of the Earth. New Ameri- 

 can Library, New York. 

 , 1960. The Creation oj the Universe. New American 



Library, New York. 

 Hoyle, Fred, 1960. The .\ature nf the [niver.se. Harper, New 



York. 

 Kuiper, Gerald P., ed., 1953, 1954, 1961. The Solar .System. 



3 vols., The University of Chicago Press, Chicago, 111. 

 /.;/f Editorial Staff and Lincoln Barnett, 1955. The World 



We Live In. Time Inc., New York. 

 Life Editorial Staff and Arthur Beiser. 1962. The Earth. 



Time Inc., New York. 

 /,(/(? Editorial Staff and David Bergamini, 1962. The Tm- 



verse. Time Inc., New York. 

 Mayall, N., M. Mayall and J. Wychoff, 1961. The Sky 



Obsemers Guide. Golden Press, New York. 

 Ross, Herbert H., 1962. .-1 -Synthesis oJ Evolutionary Theory. 



Prentice-Hall, Inc., Englewood Cliffs, N.J. 

 Strahler, Arthur N., 1960. Physical Geography. ■ 2nd ed. 



John Wiley & Sons, New York. 

 .Sullivan, Walter, 1961. .[ssault on the I'nknuwn: The Inter- 

 national Geophysical Tear. McGraw-Hill Book Co., New 



York. 

 Whitrow, G. J., 1959. Structure and Evolution of the Tnwerse. 



Hillary House Ltd., London. 

 Wilson, J. Tuzp, 1961. IGY: The Year of the .\ew .Moons. 



Alfred A. Knopf, Inc., New York. 

 Zim, Herbert S., 1956. Stars. Golden Press, New \'ork. 



