Modern Mind

said to dominate any major civilisation. As we shall see in chapters 25 and 26, a seismic change in the structure of intellectual life was beginning to make itself felt.

31
LA LONGUE DURÉE
     
    Between September and November 1965, the United States National Science Foundation vessel
Eltanin
was cruising on the edges of the Pacific-Antarctic Ocean, collecting routine data about the seabed. This ship was essentially a laboratory belonging to the Lamont-Doherty Geological Observatory, part of New York’s Columbia University. Oceanography had received a boost in World War II because of the need to understand U-boats and their environment, and since then with the arrival of deepwater nuclear submarines. The Lamont Institute was one of the most active outfits in this area. 1
    On that 1965 voyage,
Eltanin
zigzagged back and forth over a deep-sea geological formation known as the Pacific-Antarctic Ridge, located at 51 degrees latitude south. Special equipment measured the magnetic qualities of the rocks on the seabed. It had been known for a time that the magnetism of rocks for some reason reversed itself regularly, every million years or so, and that this pattern told geologists a great deal about the history of the earth’s surface. The scientist in charge of legs 19,
20,
and 21 of the
Eltanin
’s journey that time was Walter Pitman III, a Columbia-trained graduate student. While on board ship, he was too busy to do more than double-check that the instruments were working properly, but as soon as he got back to Lamont, he laid out his charts to see what they showed. What he had in front of him was a series of black-and-white stripes. These recorded the magnetic anomalies over a stretch of ocean floor. Each time the magnetic anomaly changed direction, the recording device changed from black to white to black, and so on. What was immediately obvious, that November day, was that one particular printout, which recorded the progress
of Eltanin
from 500 kilometres east of the Pacific-Antarctic Ridge to 500 kilometres west, was
completely symmetrical
around the ridge. 2 That symmetry could be explained in only one way: the rocks either side of the ridge had been formed at exactly the same time as each other and ‘occupied the position they did because they had originated at the ridge and then spread out to occupy the seabed. In other words, the seabed was formed by rocks emerging from the depths of the earth, then spread out across the seafloor – and pushing the continents apart. This was a confirmation at last of continental drift, achieved by seafloor spreading.’ 3
    It will be recalled that continental drift was proposed by Alfred Wegener in1915 as a way to explain the distribution of the landmasses of the world and the pattern of life forms.
He
took the theory for granted, based on the evidence he had collected, but many geologists, especially in the United States, were not convinced. They were ‘fixists,’ who believed that the continents were rigid and immobile. In fact, geology was divided for years, at least until the war. But with the advent of nuclear submarines the U.S. Navy in particular needed far more information about the Pacific Ocean, the area of water that lay between it and its main enemy, Russia. The basic result to come out of this study was that the magnetic anomalies under the Pacific were shaped like enormous ‘planks’ in roughly parallel lines, running predominantly north-south, each one 15–25 kilometres wide and hundreds of kilometres long. This produced a tantalising piece of arithmetic: divide 25 kilometres by 1 million (the number of years after which, on average, the earth’s polarity changes), and you get 2.5 centimetres. Did that mean the Pacific was expanding at that rate each year? 4
    There was other evidence to support the mobilists. In 1953 the French seismologist Jean Pierre Rothé produced a map at a meeting of the Royal Society in London that recorded earthquake epicentres for the Atlantic and Indian Oceans. 5 This was remarkably consistent, showing many earthquakes associated with the midocean ridges. Moreover, the further the volcanoes were from the ridges, the older they were, and the less active. Yet another spinoff from the war was the analysis of the seismic shocks sent shuddering across the globe by atomic bomb explosions. These produced the surprising calculation that the ocean floor was barely four miles thick, whereas the continents were twenty miles thick. Just a