1. DEEP EARTH PROCESSES 



An Overview of Deep-Earth Chemistry and Physics 



We recall that the earth consists of 

 three parts: a thin crust, five to forty 

 miles thick; a "mantle," below the 

 crust, extending a little less than half- 

 way down to the center; and a core. 

 (See Figure II-l) The crust is the 

 heterogeneous body on which we live 

 and grow our food, and from which 

 we derive all mineral resources, metals, 

 and fuels. It is the only part of the 

 earth that is accessible and directly 

 observable; the composition of the 

 mantle and core must be inferred from 

 observations on the surface. 



The crust, the oceans, and the 

 atmosphere above them form the en- 

 vironment in which we live. This 

 environment has been shaped through 

 geologic time and continues to be 

 shaped by forces which originate in 

 the mantle beneath it. Its nature and 

 the processes that occur in it mold the 

 environment and determine what part 

 of the surface will be land and what 

 part sea, which oceans will expand 

 and which contract, which continents 

 will move apart and which come to- 

 gether. Forces mainly within the 

 mantle determine where mountains 

 will rise, where stresses will cause 

 rocks to fracture and flow, where 

 earthquakes will occur, how intense 

 and how frequent they will be. 

 (Earthquakes, it may be recalled, 

 have killed more than one million 

 people in this century.) Most vol- 

 canoes have their source in the 

 mantle. They destroy towns and 

 crops; the gases and solid particles 

 they discharge into the atmosphere 

 contribute significantly to atmospheric 

 "pollution," in the form, for instance, 

 of huge amounts of sulfur oxides; at 

 the same time, volcanoes provide the 

 very ingredients (water, carbon di- 

 oxide) without which life would be 

 impossible. 



Figure 11-1— REGIONS OF THE EARTH'S INTERIOR 



This idealized view of the interior of the earth shows the distance in kilometers from 

 the surface to the several regions. This view is admittedly simplified; as time goes 

 on, our knowledge of the structure of the earth's interior will undoubtedly become 

 more detailed and complex. 



This interaction of crust and mantle 

 cannot be overemphasized. The whole 

 of the environment, the total ecology, 

 is essentially a product of mantle 

 activity. 



Participation of the core in crustal 

 affairs is much less clear. At the 

 moment the core is of interest mainly 

 as the source of the earth's magnetic 

 field; but there are reasons to believe 

 that it may yet play a more funda- 

 mental role in the earth's economy, 

 perhaps as a source of gravitational 

 energy or perhaps in converting some 



of the earth's kinetic energy of rota- 

 tion into heat. 



Problems and Methodologies 



Problems of the deep interior are 

 essentially (a) to determine the chemi- 

 cal composition and physical nature of 

 the materials composing the mantle 

 and core, which are nowhere acces- 

 sible to direct observation, and (b) to 

 determine the distribution and nature 

 of the energy sources and forces that 



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