"Look, that's not basalt! It's the mantle! We've made it!"
A dozen men are clustered around the end of a grimy piece of pipe. From its end a rod-shaped piece of rock about 2 inches in diameter is slowly emerging. The scene is the drilling floor of a huge derrick like the ones that dot the skyline above oil country. But. this derrick is on a ship and gently swaying with the sea's swell.
When the object is clean enough to see its details, a dozen heads close in to screen this fascinating rock.
"What is it? What have we got?"
''It looks like .. ." but the last word is indistinct.
Hopefully, in a few years the team of top U. S. earth scientists on the boat described will be able to finish off that sentence. But first they will have to successfully complete "Project Mohole." They will have to push present engineering knowledge to its limit—and beyond, to drill for the first time through the earth's crust and into its mantle. The precious sample they will then obtain will be studied for years and will yield hundreds of secrets about the earth. Long-held theories about this and other planets, many of them the results of entire lifetimes of work, will be destroyed—or supported—by that tiny 2-inch core of rock.
Physicists, mathematicians, biologists, astronomers, and geologists have been waiting for a long time for someone to obtain a deep sample of the earth underfoot, the earth no one really knows yet. But until recently, no one has dared to even dream of such a herculean probe.
For thousands of years man has pointed his biggest questions upward into the skies, achieving in the past few years the ability to hurtle a man hundreds of miles into space to learn its secrets. The best he has been able to achieve in the other direction is to sink an oil drill bit five miles and a mining shaft two miles. Now scientists are preparing to look not to outer but to inner space. They hope that their findings will tell them how the planets were formed, when this took place, and what the future holds for them. There are scores of mysteries to be unraveled from inner earth. For example:
Speculation, if not much action, concerning the earth's interior, has always been popular. In 1678, a Dutchman named Athanasius Kircher published two weighty volumes devoted entirely to the inner earth. Much of his writing was on "dragons and other dark-dwelling beasts," but the author also suggested theories of which at least 50 have since been proven by geologists. The nineteenth century saw British and German mathematicians Leslie and Euler both writing that the earth was a hollow ball with a separate fiery core at the ball's center. That century also brought Dr. Edmund Halley (discoverer of Halley's Comet), who avowed earth consisted of "three concentric hollow spheres without any openings and with a hot spherical core in the center," and Darwin, who wished "some one would bore a hole so we might see."
The earth, science has since learned, is a solid, but not rigid, ball which weighs 5,887,613,230,000,000,000,000 tons. We also know it gets hotter the deeper we descend into it. In the world's deepest gold mine, at Robinson, South Africa, the walls are so hot a $500,000 air-conditioning plant had to be installed to keep the miners from being roasted alive. Yet, the total heat coming up from below the surface is so slight it is 30 million times smaller than the amount the earth receives from the sun.
Not entirely unlike their forebears, most modern geologists believe the earth consists of a number of concentric shells of different materials, arranged in the order of increasing density. On the surface there is a thin crust of solidified granites and basalt, then the mantle, a thick layer of heavier rocks in a fairly plastic state. Next, comes a liquid outer core. Finally, there is a solid ball within the liquid, called the inner core. This supposed separation of materials probably took place in the earth's early youth. When it was still quite liquid, or even gaseous, the heavier materials easily sank to the center of the ball, where they remain still. The crust cooled off and solidified perhaps five billion years ago, but temperatures in the deep interior are believed to have been unchanged during all this time.
The crust, which varies in thickness from three to 40 miles, is thought of as a thin, comparatively soft veneer of lightweight rocks. Its most abundant metal is aluminum, estimated to make up 7.85 per cent of the crust. Beneath the sea the crust's composition differs radically from that under the land masses. The continents are seen as thick blocks of relatively light granite rock, the ocean basins as floored with a much thinner, but heavier basaltic rock. But both crust types act as though they are floating on the much denser rock of the mantle.
The mantle, comprising 85 per cent of its bulk, would be, of course, earth's largest section. It is estimated to be 1,800 miles thick and made of basalt (dark volcanic rock) or something even heavier. We know less about the mantle and the part it plays in our events than we know of the sections beneath it.
The mantle's rocks probably exist under a pressure equivilant to that of 40,000 tons of weight put on a U.S. ten-cent piece. This in turn causes mantle temperatures of at least 5,000 degrees above zero Fahrenheit. Thus, the rock bends, twists, and possibly even flows like bread dough, and the mantle may well be the reservoir of molten matter that feeds volcanoes. Seismologists are convinced it is where the severest earthquakes originate.
Below the mantle is the earth's outer core. It is about 1,300 miles thick and may consist of liquid iron and nickel. Part of the enormous heat there is caused from the pressure of the above weight, and part is thought to be heat originated when the planet was born.
Floating in this liquid is the inner core, a solid ball of 1,600 miles diameter which may be made of iron and a little nickel. The pressure (which keeps the ball compressed as a solid) is about 4,000,000 times earth's atmospheric pressure at sea level. A professor in California is attempting to prove the inner core can be moved. He claims it moved toward Japan as a result of a "kick" supplied by the Chilean earthquake of 1960. He is waiting for another strong quake to produce a "kick" that his university can measure.
Earthquakes (the results of rocks fracturing under stresses) have seemingly proved this crust-man tie-core theory of the earth's composition. Seismologists have observed that when an earthquake wave enters the core, for example, it bends twice, once as it goes in and again as it comes out. From this, they've concluded that there is a core and that its texture and weight differ enormously from the mantle. Some types of quake waves won't go through the core at all. Scientists studied them and found they won't go through liquid either. Therefore, it seems likely the core is liquid, perhaps as thick as hot asphalt.
Among other clues to the nature of the inner earth, there is the fact that the earth acts like a great magnet. Iron is the magnetic element, so the bulk of the earth should be iron. Meteorites, generally assumed to be pieces of some broken planet, also support the "iron earth" theory come in two categories: meteorites containing up to 90 per cent iron and stone meteorites which are similar in chemical composition to the rocks of the earth's surface. The conclusion seems inescapable to geologists that the difference between the two types of meteorites is due to their having originated at different depths of the disintegrated planet and that the earth contains a like composition.
Although a great deal of the foregoing is not new, the surprising thing is that at this point in world history very little of it has been proven. Until man can journey deeper into earth than he has, or obtain temperature measurements and composition samples, he will simply have no factual knowledge concerning 99 per cent of the planet he lives on. This is why the 1957 announcement of the American ''Project Mohole" created worldwide scientific interest.
"Mohole" is often modestly described as "a plan to drill a hole in the bottom of the sea." Actually, it is a considerably complicated experiment which will cost the National Science Foundation from $45 to $68 million and probably not be completed until 1967.
The plan calls for a hole which would reach through the crust, pass the Moho, and enter the mantle. The project takes its name from the Moho, the popular term for Mohorovicic Discontinuity. The latter is the narrow boundary between the crust and the mantle. It was named for the Yugoslav seismologist, Andrija Mohorovicic, who discovered the discontinuity in 1909 when, during a quake, he noticed that seismic-wave speeds abruptly increased there. Today, some geologists believe the Moho was the primordial surface of earth.
The project directors have decided that the easiest route to the Moho, and thence the mantle, is through the ocean floor. There, the crust averages just one third of the average thickness under the continents. While the aim is to sample the mantle, examination of the sediment layers on the sea floor as the drilling progresses should be an important byproduct. The layers are believed to contain a continuous record of all life forms as they have evolved.
From an ocean site where the crust is but three to five miles thick, the mantle can be reached by a drill-string 30,000 to 35,000 feet long. The string, or pipe, would pass through 15,000-20,000 feet of water, then about 15,000 feet of crust. The only hole which comes even close to this—a Texas oil probe which came up dry—went down just under five miles-25,000 feet.
Though there still remain many problems to be worked out, the project's study of American offshore petroleum technology and its own test drillings in the Pacific, both have proven the feasibility of using the standard rotary drill common to the oil industry. But this record-depth drilling will entail many peculiar and unprecedented hazards. For one thing, the floating drilling platform will have to maintain its position, perhaps for years, within a 500-foot radius circle in an average of 18,000 feet of water! Even minor drifting could snap the 4½-inch pipe. Radar targets mounted on floats and an array of sea floor-stationed sonar targets will help keep the drilling vessel positioned. And to re-enter the hole, an act comparable to threading a needle through 18,000 feet of water, the drillers may possibly use a funnel-type target at the entrance in conjunction with television and still more sonar equipment.
The bold scope of "Mohole" has sparked international enthusiasm. This was verified when late last year the Soviet Union decided also to begin a subterranean study. Thus, as is already the case with outer space, a race to conquer inner space is about to begin.
The Russian drill teams will attempt holes at five land sites—one of them up to nine miles deep—solely in the crust. Although they will be connected with oil and metal prospecting, the principal reason for the holes will be to make scientific discoveries. "Such penetration," asserts the head of Russia's Geology Institute, " is just as grandiose a task as penetrating into the cosmos!"
A spokesman for the National Science Foundation, in Washington, D. C, is equally confident of the project's success. "All we really know about earth," he has pointed out, "is by the indirect methods of geophysics. Now, man will receive actual samples ... to confirm or deny some of his theories." An additional possibility is that the first mantle core brought to the earth's surface may also answer questions no one has yet asked.
