Earth and Natural History 



Orientation 



The study of nature can begin almost anywhere. 

 One can start either with some small, even micro- 

 scopic, organism or with anything of larger size, even 

 the entire universe. Here, the start is with the uni- 

 verse, the most complex aspect of nature because the 

 universe is all inclusive, but the features of the uni- 

 verse will be barely mentioned. The purpose of this 

 introduction is to set the scene for study of one planet. 

 Earth — its air, sea, land, life, and the interrelations 

 among living organisms and their living and nonliving 

 surroundings. Even the discussion of the earth's 

 features will fall far short of what is known. However, 

 this presentation will provide some understanding of 

 nature as a single, integrated phenomenon, rather 

 than as separate units of air, sea, land, and life. In 

 other words, nature is synergistic. 



This chapter provides certain details that empha- 

 size the organization and possible origin of living and 

 nonliving things upon our planet. Moreover, it seems 

 justified to stress both organization and origin be- 

 cause both are keys to examining the nature of natu- 

 ral history. Organization is basic for studying nature, 

 and origin for seeing nature as a single evolving 

 process. 



THE ORGANIZATION 

 OF THE UNIVERSE 



The extremely complex universe can be studied 

 because it displays order in the form of units of ever- 



increasing size, each smaller unit being a part of every 

 larger one. In our discussion the smallest unit of the 

 universe is arbitrarily considered to be a star system. 

 The star system that contains our earth is called 

 the solar system; it consists of a star (the sun) and a 

 number of bodies, such as planets, asteroids, comets, 

 and others, that revolve about it. Individual planets, 

 in turn, may have orbiting bodies, or satellites. Earth, 

 for example, has a single natural satellite, the moon. 

 Other planets in the solar system may have none or as 

 many as twelve satellites (also sometimes called 

 "moons"). The asteroids (asteroid belt) are a group 

 of over 1600 very small planetlike bodies, the largest 

 being Ceres (approximately 480 miles in diameter). 

 The asteroids follow variable paths about the sun, 

 but the orbits of most of them are between the planets 

 Mars and Jupiter. Comets are generally smaller than 

 asteroids and travel in the broadest oval paths about 

 the sun. A star system, then, is composed of a star 

 and various objects that orbit about the star. 



The unit of universe organization next larger in size 

 is the galaxy. Our galaxy encompasses the solar 

 system plus millions of other star systems. The sig- 

 nificant feature of galaxy organization is that the star 

 systems are relatively close together. The most 

 widely separated star systems within a galaxy usually 

 are much closer together than is any star in one 

 galaxy to its nearest neighbor in another. This rela- 

 tively close relationship is related to the physical 

 organization within a galaxy, an organization involv- 



