Science: How Oceans Grew

United Nations headquarters on the East River was host last week to more seagoing scientists than had ever before clustered on a single spot of dry land. Over 1,000 oceanographers from 38 countries gathered for the first International Oceanographic Congress, some 500 of them prepared to read scientific papers. During the two weeks of sessions every aspect of the oceans was scheduled for a full going-over, from the microscopic diatoms that float near the sunny surface to the mysterious cracks and bulges on the pitch-black bottom.

Of the seven research vessels that tied up at Manhattan piers, the most romantic was the Calypso of France, commanded by handsome Captain Jacques-Yves Cousteau, famed underwater explorer and author of The Silent World. Displayed on her deck were weird bits of equipment: submarine scooters, deep-sea motion-picture-taking devices called “halibuts,” and an anti-shark cage. In her hold was a Diving Saucer, a two-man submarine designed to follow the ocean bottom down to 1,500 ft.

The most striking vessel was Russia’s new Mikhail Lomonosov, painted resplendent white with the earth encircled by a satellite gleaming proudly on her bow. Much bigger (5,960 tons) than most Western research ships, she carries a complement of 131, of whom 71 are scientists. She can stay at sea for four months instead of the five weeks that is average for U.S. vessels. Her equipment is lavish, e.g., six deep-sea winches instead of the customary single one. U.S. experts who looked her over agreed that she could do almost any kind of oceanographic work, and the Russians have seven ships in her class or larger.

During the opening sessions the well-financed Russians had comparatively little to say. Most striking papers came from Columbia University’s Lament Geological Observatory, whose single seagoing ship, the battered schooner Vema, is a midget compared to the Lomonosov and more than once has been embarrassed in out-of-the-way ports for lack of money to buy supplies. Lament Men Maurice Ewing and Bruce Heezen, both members of an oceanographic subspecies whose real interest is the bottom, told how the Vema’s probing-on-a-shoestring may have solved the ancient mystery of how the earth got its oceans and its solid land.

Crack in the Ridge. Lament’s theory of the earth started taking shape several years ago when electronic depth-measuring equipment spotted a peculiar crack in the top of the Mid-Atlantic Ridge, the strange underwater mountain range that snakes down the center of the North and South Atlantic. Other explorations proved that the crack followed the ridge’s top faithfully from north to south.

Oceanographers have long considered the Mid-Atlantic Ridge about the most interesting single feature of the ocean bottom. According to the original theory of continental drift, which was presented by German Geologist Alfred Wegener in 1920, the ridge was made of material left behind when North and South America broke away from Europe and Africa, and the chasm between them widened to form the Atlantic. The ridge reflects the shape of the shores on both sides of it, and it emphasizes the remarkable fact that if the New World were pushed eastward, it would fit with some precision into the western shore of the Old World.

Vema’s discovery of a crack following the top of the ridge gave Wegener’s theory a new round of attention. The curving crack might be a rift, a familiar geological feature that indicates the earth’s crust has been under tension and has pulled apart.

40,000-Mile Crack. In pursuit of this theory the Lamont men, soon helped by other oceanographers, followed the crack in the sinuous ridge. Sometimes they spotted it on new depth charts, sometimes on old ones. When they noticed that many shallow earthquakes came from under it, they searched seismograph records for similar earthquake centers in unsounded parts of the oceans. By last week the Lamont men could trace the cracks 40,000 miles clear around the earth (see map). As in the Atlantic, the cracks generally follow the tops of rises in the ocean bottom. They stay midway between large land masses, but in a few places they run ashore, forming, for instance, the steep-sided Jordan Valley and the famous rift system in East Africa which contains both Lake Tanganyika and the Red Sea. Another crack runs ashore in Mexico, to form the Gulf of California and the Imperial Valley.

Ur-Continent. Lamont men think the cracks may be proof that the continents indeed drifted away from each other, and are still drifting. Dr. Ewing recalled a theory of Venig Meinesz, who suggested that the early earth may have lacked the dense central core that it has today. Its hot, fluid inside material could circulate unhampered in a single “cell,” rising to the surface on one side of the sphere and sinking down on the opposite side after cooling by radiation into space and getting heavier. When this had gone on long enough, all the light rock on the earth’s surface was gathered in one hemisphere as a single “ur-continent.”

Later, according to Meinesz, the earth formed a dense core that stopped the single-cell circulation. Then, the molten inner material was forced to circulate in smaller cells which reached the surface in several places. This spelled trouble for the single continent. One of the streams of material rose beneath it, split it asunder and moved the pieces apart.

The rifts indicate this process may be still continuing, perhaps helped by an expansion of the earth. As Heezen sees it, the earth’s crust breaks under this tension from within, forming a narrow, steep-sided rift that grows slowly wider. When the rift is about 60 miles wide, a fresh rift forms in its center. More rifts form as long as the tension continues, and their steep sides accumulate in a broad band of rugged terrain on both sides of the youngest rift. Since the tension is caused by rising molten material, this cracked-up region is apt to be somewhat elevated, like the Mid-Atlantic Ridge.

Heezen thinks that the Atlantic Ocean is a very old crack that has rifted over and over and grown 3,000 miles wide. Its sides may still be moving apart at the rate of about one yard in 1,000 years. At the other extreme are young rifts like those in East Africa that have not had time to split more than once. Eventually they may grow into oceans as wide as the

Atlantir. The rift that strikes north from the Gulf of California may some day, many millions of years away, put ? broad ocean between Los Angeles and the rest of the U.S.