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.