Project Mohole is this country’s scientific effort to explore and sample all layers of the earth’s crust and the underlying mantle.
The need for such a project is basic: the mantle comprises about 84 per cent of the earth’s volume. When geologists and geophysicists know its composition and physical properties, they will be able to reason more intelligently about the earth.
There is also a possibility that knowledge of the mantle may be applicable to other planets in this solar system, for many scientists now believe that all of the planets were created at about the same time and may be similar in composition. Thus, exploration of inner space may contribute to exploration of outer space.
The most favorable sites for drilling to the mantle are in certain areas of the deep ocean basins where the crust is thinnest. At the site recently selected for Mohole drilling in the Hawaiian Islands, the mantle lies only 6–7 miles below sea-level. In contrast, the depth to the mantle beneath the continents averages about 20 miles.
The idea of drilling to the mantle from a floating vessel in deep water was first conceived in 1957 and, with National Science Foundation funds, Phase I of Project Mohole was completed in 1961 off the coast of lower California. The objective of this part of the Mohole program was to prove that the ultimate goals of the project were feasible by carrying out a shallow drilling (coring) program in deep water from a floating vessel.
In this respect, Phase I was successful; in 1962, the National Science Foundation initiated Phase II of Project Mohole. The purpose of Phase II is to achieve the original objectives of the project—making the penetration of the crust and mantle as meaningful as possible through collection and study of rock samples and scientific measurements to be made in the hole both during and after completion of drilling.
The technical problems which confronted the Phase II Mohole staff, when it was organized in 1962, could be grouped in three general classifications. The first involved the design and construction of a stable and safe base for deep-ocean drilling operations to be carried out on a year-round basis. The second involved increasing drilling capability sufficiently to reach the 30,000-35,000-foot mantle depth. (This depth is 20–40 per cent greater than the deepest well ever drilled.) The third concerned the development of measurement and sampling techniques to insure maximum scientific productivity from the effort.
Phase II of Project Mohole is now well under way, and many problems have been solved. The basic design of a stabilized drilling platform with a dynamic positioning system is virtually complete, and some of the prototype models of new drilling tools developed by the project recently were tested in a well drilled in basaltic rock near Uvalde, Texas. Also, new logging and coring equipment has been tested successfully in the same hole.