402 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



The geophysical logging hole reached a total depth of 576 feet, and 

 penetrated to 20 feet within the basaltic layer. Geophones and seismic 

 wave detectors were lowered into the hole to measure the velocity of 

 sound in the deep rocks and to redetermine the thickness of the various 

 layers beneath the reach of the drill. Preliminary analysis of the 

 reading indicates that sound waves penetrate the soft sediment at a 

 rate of 1.69 kilometers per second, a rate considerably less than the 

 value generally assumed by seismologists. If this low velocity gener- 

 ally exists, oceanographic sediments could be thinner than has hereto- 

 fore been supposed. 



The geophysical logs also measured the heat flow coming through the 

 layers of the earth beneath the ocean. These measurements provided 

 improved scientific estimates of the earth's internal temperature. 

 Readings off Guadalupe Island at 500 feet below the ocean floor showed 

 a somewhat higher heat flow than was expected on the basis of earlier 

 bottom measurements. The significance of this is not yet understood, 

 but it is interesting in view of the fact that, while the heat flow through 

 the ocean floor is less than that measured on land, it is still far too high 

 to satisfy some theoretical considerations. According to present 

 theories, heat flow through the oceans should be less than has been 

 observed. 



Most of the continental heat flow from within the earth derives from 

 radioactive elements in granitic rocks. But the rocks thought to com- 

 pose the oceanic crusts are supposedly low in radioactive material. 

 Scientists believe, therefore, that there must be a suboceanic heat 

 source other than the crust. There are many suggested explanations 

 including an unsuspected radioactive heat source high in the mantle, 

 or convection currents within the mantle. 



A more exact understanding of suboceanic heat flow will also pro- 

 vide new information that can be fitted to current theories of the 

 earth's origin and to the conjectures of whether the earth is heating 

 or cooling. It may also be possible to determine how much of the 

 suboceanic heat is primordial and how much derives from radio- 

 activity. 



What may be the first fixed-position current measurements in the 

 deep ocean were reported by the Mohole scientists. A velocity of 0.2 

 knot was observed at 1,500 feet in measurements for as long as 9.5 

 hours with a rotor-type meter suspended between the drilling ship 

 and one of the deep-moored buoys. This velocity was considerably 

 less than estimates used in designing the drilling string. 



ONLY A BEGINNING 



Present scientific and engineering results are only the beginning. 

 Project Mohole, born as a purely scientific concept, has led to the 



