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Project Mohole was an attempt to retrieve a sample of material from the earth's mantle by drilling a hole through the earth's crust to the Mohorovicic Discontinuity, or Moho. The project was suggested in March 1957 by Walter Munk, NAS member (1956) and member of the National Science Foundation (NSF) Earth Science Panel.
Project Mohole represented, as one historian has described it, the earth sciences' answer to the space program. If successful, this highly ambitious exploration of the intraterrestrial frontier would provide invaluable information on the earth's age, makeup, and internal processes. In addition, evidence drawn from the Moho could be brought to bear on the question of continental drift, which at the time was still controversial.
The Mohorovicic Discontinuity marks the boundary between the earth's crust and mantle. (The Moho was named for Andrija Mohorovicic, a Croatian geologist who first proposed the existence of such a discontinuity.) The plan was to drill to the Moho through the seafloor, at those points where the earth's crust is thinnest. Attempting such an effort on land would have been impractical, since the drilling equipment would not have withstood the depths and temperatures involved. Ocean drilling offered a further advantage in that undersea samples, undistorted by atmospheric and surface actions, would provide better evidence of long term geological activity than would samples drawn from land.
The American Miscellaneous Society (AMSOC), an informal group of scientists of which Munk was a member, endorsed Munk's idea. The group was formed in 1952 when Office of Naval Research geophysicists Gordon Lill and Carl Alexis found themselves handling research proposals that fit into no existing scientific categories. Out of that "precarious miscellany" AMSOC emerged, as a forum for scientific speculation. When funds for Project Mohole had been obtained from NSF, AMSOC in 1958 took charge of the effort as an official study unit of the National Research Council's Division of Earth Sciences.
Project Mohole was to include three phases, the first consisting of an experimental drilling program, the second consisting of an intermediate vessel program, and the third consisting of the final drilling to the Mohorovicic Discontinuity. After ocean-going trials off La Jolla, California, Phase I began in earnest with a set of drillings off Guadalupe, Mexico, in March and April 1961. Five holes, one of which extended 601feet beneath the seafloor, were drilled under 11,700 feet of water. Cores obtained from the holes showed that the first layer of crust extended 557 feet and consisted of sediment Miocene in age. The second layer of crust was sampled for the first time, and this was found to consist of basalt. After the unprecedented success of Phase I, it was decided to shift operational control to NSF while maintaining the AMSOC Committee as project adviser. This relationship proved to be unsatisfactory, and after a series of negotiations and redefined agreements with NSF, the AMSOC Committee in 1964 dissolved itself. Following the AMSOC Committee's dissolution, two new National Academies committees continued to advise the NSF Mohole activity until Congress, objecting to increasing costs, discontinued the project toward the end of 1966, before Phase II could be implemented.
Although Project Mohole failed in its intended purpose, it did show that deep ocean drilling was a viable means of obtaining geological samples. Since Mohole's demise a number of related programs have been undertaken, the most recent one being the NSF's Ocean Drilling Program.