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During the past year leading news 

 magazines and popular periodicals 

 have drawn attention to a project aimed 

 at the drilling of a hole through to the 

 earth's mantle. This is the so-called Mo- 

 hole project, which is currently under 

 way. Most of the accounts published 

 thus far have done little to establish the 

 purposes and aims of the venture. Nor 

 has much been said concerning the back- 

 ground history that has led up to it. The 

 reporting has been largely concerned 

 with the difficulties involved. One leaves 

 these reports with the impression that 

 the project is interesting — but why both- 

 er? In this article, we hope to change 

 that impression by adding a little depth 

 to the bare fact that a group of individ- 

 uals have taken upon themselves the 

 enormously difficult task of drilling a 

 hole into the earth to a level where they 

 will intersect a vague object with the im- 

 probable name of The Mohorovicic Dis- 

 continuity. 



Over the past hundred years geolo- 

 gists have accumulated an extensive and 

 impressive knowledge of the history and 

 processes operating in the genesis of the 

 continents which make up about one- 

 third of the earth's surface. The oceans 

 which cover the remaining two-thirds of 

 the surface are still largely a mystery. 

 However, during the International Geo- 

 physical Year (1957-1958) considerable 

 progress was made in a concerted study 

 of the oceans and their basins. Under 

 this impetus oceanographic research is 

 expanding yearly. However, we still do 

 not have any direct knowledge of the 

 earth's interior. Up to now our informa- 

 tion about the constitution of the bulk of 

 the earth has been derived by inference 

 chiefly from three sources: 1) If we as- 

 sume that meteorites are fragments from 

 the interior of a disintegrated planet sim- 



ilar to the earth, then we can draw rea- 

 sonable conclusions about the interior of 

 the earth itself. 2) The effect of the 

 moon's pull upon the earth and its o- 

 ceans (the tides) can be measured with 

 considerable accuracy. If, then, several 

 hypotheses are made concerning the 

 composition and structure of the earth's 

 interior, we can compute the effect that 

 this pull should have under each hypoth- 

 esis. The computation which comes clos- 

 est to the observed values presumably is 

 the best one. Nevertheless, the picture it 

 yields of the earth's interior is still hypo- 

 thetical. 3) During earthquakes and 

 major volcanic eruptions the shock waves 

 that move through the earth can be de- 

 tected by sensitive instruments called 

 seismographs. By interpreting the paths 

 and velocities of these shock waves, in- 

 ferences can be made concerning the 

 composition and structure of the interior. 



The third method listed above has 

 been the most fruitful in giving indirect 

 information on the earth's interior, and 

 for our purposes here it is worthwhile 

 describing a few of the major features 

 of the science of seismology. 



An earthquake is caused by the mo- 

 tion of one portion of rock against an- 

 other along a fracture called a fault. The 

 motion is generally not large at any one 

 time; movements of less than one foot 

 are most common. However, repeated 

 movements along the same fault over 

 several million years can result in thou- 

 sands of feet of total displacement. The 

 fault fracture itself may not necessarily 

 extend up to the surface of the earth at 

 all. In fact, most of them do not. They 

 commonly die out gradually over thou- 

 sands of feet just as most of the fractures 

 in a shattered window pane die out be- 

 fore reaching the edge of the window. 

 Thus, earthquake tremors are generated 



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