The Age of the Ice Age

To anthropologists, man is the child of the Pleistocene ice age, that period beginning roughly 1,000,000 years ago when he was forced to adapt to fierce variations in climate, and when the brutalities of nature hastened his evolution from the apes. Dating the period precisely has always been difficult. On land, erosion has obliterated almost all trace of the Pleistocene's earliest glaciers. On most parts of the cold, quiet ocean bottom, where remnants of prehistory have survived, ancient sediments have piled up too deeply for convenient study. The cylindrical cores that have been brought up have not reached down to layers deposited at the beginning of the ice age. So scientists have long puzzled over the proper Pleistocene timing; they have wondered whether the start of the ice age came suddenly or insidiously, whether its deep chill affected the whole earth.

This week, in the magazine Science, Oceanographers David B. Ericson, Maurice Ewing and Goesta Wollin, of Columbia's Lament laboratory, offer new and promising evidence on all these questions. The oceanographic trio discovered that on sloping parts of the ocean bottom, earthquakes sometimes make the sediments "slump." Layers many feet thick are suddenly stripped away, leaving ancient sediments bare. If enough sediment is removed, the normally inaccessible base of the Pleistocene is left within reach of the oceanographers' tools.

Discoasters' End. After studying more than 3,000 cores brought back by 43 voyages, the Lamont team found eight that seemed to reach back far enough. Four came from near the Bahamas, two from mid-Atlantic, one from near Brazil, and the eighth from the Indian Ocean. All showed a band 4 in. to 6 in. wide marking a sudden change in the remains of small ocean creatures. Below the band the sediment is full of discoasters, the tiny star-shaped fossils of ancient, single-celled plants. Above the band no discoasters can be found. Apparently, they died off suddenly. So did other kinds of tiny, freely drifting creatures, while new kinds appeared just as suddenly.

The oceanographers point out that the discoasters and their associates had thrived for many millions of years in the warm, unchanging oceans before the Pleistocene. The narrow band of sediment in which their extinction is recorded, represents a period of less than 6,000 years, and in this short time--which is almost no time at all on the geological scale--something drastic must have happened to the water in which they lived. Best bet is that the change was a sudden cooling that marked the beginning of the Pleistocene, when the first great glaciers were creeping over the continents. Since parts of the eight cores are missing, the age of the band of extinction cannot be set exactly. But the Lamont men are reasonably sure that it is at least 800,000 years old and may be a great deal older. This is just about enough time for man's ancestors to have developed into true humans.

Inconstant Sun. Why did the earth get suddenly colder? The Lamont men do not know for sure, but they say that the suddenness of the change rules out the rise of new mountain ranges that might have interfered with the free circulation of the atmosphere. That speculation, long popular among scientists, is no longer satisfactory; mountains simply do not grow fast enough.

Dr. Ericson favors a theory that holds that during the ice age the sun went through periods in which it generated less heat. It recovered during the warm interglacial periods and melted most of the glacial ice. But there is no guarantee against another relapse. Modern man may be enjoying an interglacial period that may end at any time. When the chill returns, it will probably send many modern species to join the discoasters.

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