EARTH AND NATURAL HISTORY ORIENTATION 



a direct reflection of individual speeds at the time of 

 galaxy formation. 



STAR AND PLANET LIFE HISTORY 



There are many theories about how a star or star 

 system is formed and is destroyed. Some of these 

 propose that the earth, for example, was once a fiery 

 ball; others do not. The theory treated here is not 

 necessarily the best one, but it is employed because 

 it is relatively simple and provides an easy framework 

 for considering the origin of the land (lithosphere) , 

 water (hydrosphere), air (atmosphere), and the living 

 world (biosphere). The formations of stars and planets 

 are here considered part of a single process. How- 

 ever, there are two possible courses in this process, 

 one leading to multiple stars like Alpha Centauri and 

 the other to a star (or perhaps a few stars) and 

 planets. 



STAR AND PLANET FORMATION 



The first step in the formation of a star involves 

 gravitational attraction, contraction, and rotation of 

 sparse gases and cosmic dust particles to form a single 

 cloud. As contraction occurs, internal pressures and 

 temperatures rise; finally, a collapse of matter toward 

 the center of the cloud results in the birth of a new 

 star. 



According to the theory employed here, a new star 

 can be involved in three possible developments. Most 

 new stars split, forming two stars. Other new stars 

 will split into three, four, five, or even more stars. 

 However, in 1 per cent or less of the cases, another 

 series of events occur. Around the new star, there are 

 also rings of matter, each ring generally in the posi- 

 tion of the future orbit of a planet or belt of asteroids 

 (Figure 1.2). Within one of these rings of matter a 

 concentration representing the earliest stage of planet 

 formation may in turn possess rings that will develop 

 into moons. At this time, there is probably no real 

 distinction between future planet and future satel- 

 lites, but later the innermost whorl or whorls form the 

 planet and outer whorls its moons. In the case of the 

 earth, a primary inner whorl may have formed the 

 earth and a primary outer whorl the moon. 



Further discussion of planet and satellite formation 

 is limited to our planet and moon. 



Figure 1.2 One hypothesis of star and planet formation. Grovita- 

 tionol attraction of goseous particles has formed a stor, planets, and 

 a satellite of the third planet. 



EARLY EARTH DEVELOPMENT 



According to the hypothesis being followed, the 

 early earth and moon were fiery balls without hard 

 outer crusts. While molten, the earth materials and, 

 to a lesser extent, those of the moon were layered 

 so that the heaviest materials formed the cores and 

 the lightest the crusts. In the case of the earth, this 

 resulted in three divisions: an inner and heaviest core 

 about 4300 miles in diameter, possibly solid inside 

 and liquid on the outside, both parts composed pri- 

 marily of nickel and iron; a middle layer about 2000 

 miles thick, the rigid yet plastic mantle: and the crust, 

 10 to 30 miles thick (Figure 1.3). Although the 

 mantle is probably rich in the mineral olivine (a 

 magnesium silicate containing iron and oxygen), 

 evidence indicates that it, like the core, contains two 

 subunits, an innermost transition layer composed 

 chiefly of silicates impregnated with iron and an outer 

 layer composed largely of silicon and magnesium. 

 The crust also consists of two parts, the basement of 

 10 to 20 miles of basalt, a heavy rock, and the top of 

 about 10 miles of the lighter granite. The basalt 

 tends to reach the surface of the crust in ocean bot- 

 toms and the granite to form the foundations of the 

 continents. 



At the time of a molten earth, gases (mostly water 

 vapor and carbon dioxide) because of extreme heat 



