DEEP EARTH PROCESSES 



are believed to cause it to act as a dy- 

 namo and to produce electric currents 

 and magnetic fields. The theory of the 

 process is one of the most difficult 

 branches of theoretical physics. Its 

 study is closely related to a wide 

 range of problems concerning the mo- 

 tions of liquids and gases in the 

 presence of magnetic fields, especially 

 to the problems of generating thermo- 

 nuclear energy. 



But no realistic treatment of the 

 earth's dynamo has yet been given. 

 The subject does not require a 

 large-scale organized attack. It needs 

 thought and ideas that will come from 



a few knowledgeable and clever peo- 

 ple. It is a subject for the academic, 

 theoretical physicists with time to 

 think deeply about difficult problems 

 and with access to large computing 

 facilities. 



Perhaps the field's oddest feature is 

 that, as already noted, it occasionally 

 reverses direction (most recently, per- 

 haps, about 10,000 B.C.). Some scien- 

 tists have suggested that these rever- 

 sals have profound biological effects, 

 that whole species could become ex- 

 tinct, perhaps as a result of a large 

 dose of cosmic rays being let in as the 

 reversal takes place. There is some 



observational evidence to support this 

 thesis. Other scientists do not believe 

 that this would happen, however, and 

 do not regard as conclusive the ob- 

 servational evidence for extinction of 

 species at the time of reversal. The 

 matter is clearly of some importance. 

 At various times in the past, the 

 majority of all forms of life are known 

 to have been rather suddenly ex- 

 tinguished, and this is a phenomenon 

 we would do well to understand. If 

 reversals of the magnetic field might 

 play a part in this drama, then we 

 have added reason for understanding 

 their cause and their effects. 



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