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SOME OF THE SCIENTIFIC AND TECHNICAL ASPECTS OF PROJECT MOHOLE
As a result of combining the evidence obtained from the study of meteorities, seismic waves, earth magnetism, heat flow and gravity, it is generally believed that the interior of the earth is divided into two main zones: the core and the mantle. The core is thought to be composed of a nickel-iron mixture; the mantle of a material similar to peridotite. No one is certain. Above the mantle is a thin slag-like covering of lighter rocks called the crust-and this is the only part that man customarily sees. The boundary between crust and mantle, defined by Professor Andrija Mohorovicic as the depth at which seismic waves abruptly increase in velocity, is now commonly known as the Moho. These general relationships are shown in the diagram below. Thus a hole to the Moho will pass completely through the crust and sample the earth's mantle.
The crust is composed of two distinct kinds of material: Continental (granitic) rocks which have an average thickness of about 25 miles and Oceanic (basaltic) rocks which have an average thickness of about 4.5 miles. These great masses of rocks appear to float in isostatic equilibrium on the surface of the mantle which behaves like a very viscous liquid. The waters of the earth which have risen to the surface during the long period of geologic time have collected in the lowest areas, atop the thin basalt, to form the oceans. The average depth of the ocean is about 12,000 feet, so if this is added to the rocky crust, the average depth to the Moho from the surface of the ocean is about 35,000 feet. The Mohole Project represents our first attempt to explore the deep crust and mantle beneath the sea. It will open this vast and little known region of the earth for the first time to the direct analysis of science and this will give us a better understanding of the earth as a planet. One might say that it will change geology and geophysics from a two-dimensional to a three-dimensional subject. Nearly three years of hard analysis, research and development has proved to the Foundation that a very large, self-positioning and highly stable platform will be required to reach the mantle. It should be noted that the deepest hole on land has penetrated to a depth of 25,340 feet and that to reach the mantle we may have to extend this depth to 35,000 feet below sea level which includes 15,000 feet of sea water and 20,000 feet of crust. To do this at sea requires as much stability as we can design into our platform. Only through stability and accurate positioning can we reduce the stresses on the drill stem and riser casing so that they will not break apart during the operation. Eight platform configurations and 21 separate designs were carefully analyzed before we reached this conclusion. The platform we have designed has been thoroughly analyzed by the country's most competent naval architects and has been subjected to model basin tests and special computer calculations.
By drilling through the crust and on into the mantle as far as possible, we will obtain the following kinds of information:
1. A better age determination for the earth.
2. A determination of the age and origin of the ocean basins and their contained sea water.
3. A better understanding of how the earth-moon system came into being.
4. An understanding of the distribution of the chemical elements in the earth, which in turn bears on the origin of the sun and perhaps other stars.
5. An understanding of the origin of continents and whether or not they are drifting about on the earth's surface.
6. Knowledge of the mantle's composition and the origin of magnetic and gravity anomalies that have been discovered beneath the sea.
7. A better understanding of the origin of life and the carbon cycle with which it is closely connected.
Not only is such information of importance in understanding the earth on which we live but also it is vital if we are to understand the rest of the solar system which is now being explored through the space program. The origins and structures of the moon and other planets will become clearer as will the reasons why they are different in so many ways from the earth itself.
With regard to the earth-moon relationships, which are creating so much excitement at this time, it is interesting to note that scientists in the Soviet Union are reported to have obtained measurements of the radioactive background of the moon and that these measurements are very similar to the radioactive background of basalt, or volcanic lava. They have interpreted this to mean that the moon could not have originated from the earth since continental rocks have a higher radioactive background than that which they found on the moon. It is possible that the Soviets have misinterpreted their findings for the following reasons. An analysis of basalt obtained from the deep sea crust during Project Mohole's Phase I shows that oceanic basalt is very low in radioactive elements such as potassium, thorium and uranium and that its background is comparable to that reported by the Soviets for the surface of the moon.
Furthermore, later work on oceanic basalts is strongly indicating that almost all of the earth's marine crust and, possibly, a good portion of the lower part of the earth's continental crust is composed of this kind of basalt which would indicate, of course, that the earth and moon may be very closely tied together so far as their origin is concerned.
Moreover, oceanic basalts must have originated from the mantle and their low radioactivity reopens the whole question of the origin of the earth's heat and how it is delivered to the earth's surface. If the reported Soviet measurements withstand the test of time, and if Project Mohole continues to stimulate further work of U. S. geochemists and geologists, it is likely that we can reach a reasonable solution for the origin of the earth-moon system for the first time. It should be noted as well that the same chemical data on oceanic basalts, when compared with certain types of meteorites, also suggests that the earth and moon may have had similar origins. While it still seems, for many complex reasons, to be unlikely that the moon was torn from the earth during the early history of the solar system, new kinds of calculations now in process have not as yet disproved this possibility.
The recent development of a new hypothesis on the origin of linear magnetic anomalies over the oceans opens up a possibility of understanding convection within the mantle and may place limits on its velocity. The size and shape of the magnetic anomalies indicate that their origin cannot be more than 35,000 feet deep and perhaps is in the upper 3,500 feet of the oceanic crust. Mohole drilling through the crust should provide answers to the question of mantle convection which would have a large impact on the problems of the earth's interior. Drilling to solve the problems associated with these magnetic anomalies is included as a part of of the Foundation's intermediate Mohole drilling plan and is currently under extensive review.
The foregoing account of recent developments in the scientific aspects of Project Mohole adds to the general scientific excitement that has always been present in the program and which is based on a desire to solve some of the great geological problems of all time. For example, how did rocks which form the continents become differentiated from those that form the deep ocean crust. After the continents were formed, have they in fact drifted about on the surface of the mantle through the geologic time and in fact are the continents still drifting? There is a growing amount of evidence that would indicate that the continents have drifted while, at the same time, new theories are being proposed in attempting to prove that the continents cannot possibly have drifted. Drilling into the deep sea crust will either add to, or detract from, the belief in continental drift depending upon whether or not extensive thicknesses of sedimentary rocks are found in the deep sea basins. If the ocean basins as we see them today are permanent features, then the continents cannot have moved and we should find in the neighborhood of 10,000 feet of sedimentary rock beneath the sea. If the sedimentary rocks are not present, then the ocean basins cannot be permanent or near permanent features and the continents may well have drifted.
The problem of continental drift has a direct bearing upon the amount of carbon dioxide that may be stored in the rocks beneath the sea in the form of limestone (CaCO3) or dolomite CaMg (CO3)2. This in turn affects our estimates of the carbon cycle during past geologic ages as well as our estimates of the carbon cycle today. If we are to effectively account for the carbon we must know how much is in the rocks, in the seas as calcium bicarbonate, in the atmosphere as carbon dioxide, in the plants and animals, and what the rates of exchange are among them all. The origin of life on earth and the various forms life has taken in geologic history is also intimately involved with our understanding of the carbon cycle. In addition, if very old sedimentary rocks are found at the
base of the oceanic crust, we may also find fossil remants of earlier forms of life than are presently known, and this would help to fill some of the gaps in our knowledge of the evolution of life.
Some of the theories of the origin of the universe, and of the stars within the universe, are based upon our knowledge of the distribution of the chemical elements. The primary base line available to the astrophysicist is his knowledge of the distribution of the elements in the earth. This knowledge is inadequate
since 85% of the earth is in the mantle and it has never been sampled. Finally, it should be noted that within the earth's mantle lie the sources of stress that cause the great tectonic features that confront the geologist. These all must somehow be explained: volcanism, mountain building, earthquakes, continents and oceans. The geologist has always had to rely upon what he finds in the rocks in order to interpret the history of the earth and to infer the processes that have operated to produce the features at the earth's surface. First, he collected evidence from the field. Then, especially during the last 20 years, he has been greatly assisted (and at times even surpassed) by the physicist, chemist, and hydrodynamicist. But now, having gone around the circuit through postulate and theory, we find ourselves back once again with the rocks. The reason is simple. Our theories about the earth have been invented largely from what we know of less than 1% of its volume and 30% of its surface. We have never had rocks from the deep crust or the mantle, and until quite recently, we have not even had rocks from the top of the crust in the deep sea basins. As in all science, we must now check theory with direct evidence if we are to progress. Theories that are not verified remain sterile.
In addition to its scientific contributions, the Project is making engineering advances which are contributing to the broad field of marine engineering and which are of interest to industry and to other Government agencies which must concern themselves with the sea. For example, the Department of the Navy has informed the Foundation that stable platforms of a design similar to the Mohole platform would be useful for submarine rescue backup, for replacing or removing heavy deep sea anti-submarine warfare equipment, for searching for, and recovery of, lost equipment from the sea floor, and as a stable oceanic research station. In addition, NASA has expressed interest in the Mohole platform for its possible uses as a marine satellite tracking station, for testing various kinds of dangerous new rocket fuels at sea, and for stabilized marine launching stations.
At the moment, the greatest industrial interest in the Mohole platform and its associated equipment has been expressed by the petroleum and offshore drilling industries. It is expected that as our petroleum reserves are depleted. the industry will move seaward to the deeper waters of the continental shelf, and that to do so they may require highly stable drilling platforms such as the one we have designed. Mohole development has also perfected the hydraulically driven turbocorer and has developed a promising wire line retractable drilling bit which can be used with the turbocorer in a highly efficient manner. For example, the drilling life of the turbocorer has been doubled which, when coupled with its high rate of penetration through hard, dense rock, will reduce the drilling time enormously. Furthermore, the use of the retractable wire bit would mean that we would not have to remove tremendous lengths of drill stem from the hole when it was necessary to change bits as they wear out.. This particular development has created a lot of interest in the drilling industry and it is confidently expected that the combination described here will be placed on the market in a reasonably short time.
The automatic pipe handling system which has been developed for Project Mohole is also of interest to the drilling industry since the rapidity with which it will run pipe into the hole or retrieve it from the hole also cuts down on drilling time and will help reduce drilling costs. This system has been automated to the extent that the complete life history of each section of drill pipe will be retained on computer tape so that sections of pipe which are approaching their failure point can be automatically removed from the drill string and discarded. Thus, the chance for a disastrous drill stem failure at great depths has been reduced as much as the present state of the art will permit.
This brief review shows that there is a scientific national need to sample the earth's mantle in order to check its chemical nature and structure. The work accomplished to date is already demonstrating that we may expect rather large scientific and engineering benefits as a result of meeting this national requirement.
MOHOLE PROJECT COST ESTIMATES
The most meaningful way to think of the cost of the Project is in two parts. The first part is the capital investment-the cost of designing and constructing the drilling platform with its attendant drilling equipment, scientific equipment, etc. The second part is the cost of operating or using the drilling platform as a scientific facility to carry out the research mission for which it is intended. Closely related to the latter, but of intrinsic scientific merit in their own right, are certain site selection and oceanographic investigations carried out during the development period.
We have tried over the years to keep the Subcommittee informed as to the estimates of these costs, but it may be well to review them here since they have changed many times as research, development and design work has progressed, as engineering estimates have become more firm, as bids have been received, and as systems engineers have tied the various systems into an integrated unit. Appreciable increases have also been caused by the increased level of economic activity in general.
The following table shows the cost estimates we have used since I first testified before this Committee in 1963. In order to show the estimated total investment prior to the operational period (dated from Government acceptance of the completed platform) we have added to the estimated capital costs ($81.4 million) the prime contractor costs for site selection and oceanographic investigations ($1.7 million) to obtain the estimated total prime contractor costs prior to acceptance ($83.1 million) and have, in turn, added estimated expenditures for other grants and contracts ($2.5 million) to give the total estimated costs prior to acceptance ($85.6 million).
1 Not based on analytical estimates.
2 After new estimate and shipyard bids.
• Figures do not include $2,000,000 shown in early estimates for sea testing since the concept was later changed. Does not include cost of scientific analysis of the cores.
NOTE. All estimates include contractor's fixed fee of $1,800,000. prorated among entries. In June 1966 estimate $1,370,000 is allocated to preoperational costs, and remainder to operations over a 3-year period.