PART II— DYNAMICS OF THE SOLID EARTH 



and water transport, harbors, and re- 

 sort beaches. When a drainage system 

 cuts through a large mineral deposit, 

 it dumps its load of partially oxidized 

 and soluble metal salts into down- 

 stream waters. 



In order to measure environmental 

 pollution and change, it is necessary 

 to know the base levels of natural 

 pollution and their distributions and 

 dynamics in space and time. The 

 response to thermal pollution in rivers 

 can be predicted on the basis of ob- 

 serving the ecology of warm waters 

 in tropical regions. The same applies 

 to oceanic waters. Natural variations 

 in radioactivity provide us with sta- 

 tistics on the effect of a widely 

 dispersed distribution of radioactive 

 wastes. Variations in the trace-ele- 

 ment abundances in natural waters 

 and soils give us an insight into the 

 effect of these on biological systems. 

 Thus, it can be said that a study of 



the geochemical and geological dis- 

 tributions and processes forms a nec- 

 essary base for the observation of 

 perturbations to the natural levels 

 and rates. 



Atmospheric Changes 



The history of climatic change, as 

 different land masses approached or 

 receded from the equator, has left its 

 record on the ecology and on surface 

 deposits. In addition, evolutionary 

 change of living organisms has super- 

 imposed progressive changes in the 

 chemistry of the earth's surface. 

 Thus, early in earth's history, great 

 thicknesses of banded iron formations 

 resulted from a combination of evolv- 

 ing bioorganisms and the atmosphere 

 of the time. 



Atmospheric change has been 

 closely coupled with the evolution of 



photosynthesis processes and, more 

 recently, with the nature and extent 

 of land areas in the more tropical 

 regions of the earth. There is good 

 evidence to indicate that the partial 

 pressures of oxygen and carbon diox- 

 ide in the atmosphere are significantly 

 different from those in the past, with 

 some estimates indicating a drastic 

 variation in the content of oxygen in 

 particular. An understanding of the 

 balance between major tropical forest 

 areas, such as in the Amazon region, 

 and the partial pressure of oxygen in 

 the atmosphere would be of some sig- 

 nificance. But precise measurements 

 of the rate of change of oxygen 

 partial pressure with the oxygen- 

 generating living systems on land and 

 in the oceans have not been made on 

 a time-scale of interest to human 

 existence. We therefore know little 

 of the short-term effects that might 

 result from a substantial change in 

 human land use. 



34 



