Modern Mind

year before the
Eltanin’s
voyage, Sir Edward Crisp Bullard, a British geophysicist, had reconstructed the Atlantic Ocean margins, using the latest underwater soundings, which enabled 1,000-metre depth contours to be used, rather than sea-level contours. At that depth, the fit between the continents was even more complete. 6 Despite these various pieces of evidence, it wasn’t until
Eltanin’s
symmetrical picture came ashore that the ‘fixists’ were finally defeated.
    Capitalising on this, in 1968 William Jason Morgan, from Princeton, put forward an even more extreme ‘mobilist’ view. His idea was that the continents were formed from a series of global, or ‘tectonic,’ plates, slowly inching their way across the surface of the earth. He proposed that the movement of these plates – each one about 100 kilometres thick – together accounts for the bulk of seismic activity on earth. His controversial idea soon received support when a number of ‘deep trenches’ were discovered, labelled subduction zones, up to 700 kilometres deep, in the floor of the Pacific Ocean. It was here that the sea floor was absorbed back into the underlying mantle (one of these trenches ran from Japan to the Kamchatka Peninsula in Russia, a distance of 1,800 kilometres). 7
    Continental drift and the wanderings of tectonic plates (many geophysicists prefer the term
blocks)
were initially of geological interest only. But geology is a form of history. One of the achievements of twentieth-century science has been to make accessible more and more remote areas of the past. Although these discoveries have arrived piecemeal, they have proved consistent – romanticallyconsistent – in helping to provide the basis for one story, one narrative, culminating in mankind. This is perhaps the crowning achievement of twentieth-century thought.
    In the same year as the
Eltanin’s
crucial voyage, twenty-seven scientists from six nations met at a conference at Stanford University in California to consider how America had been populated. These were members of the International Quaternary Association – geologists, palaeontologists, geographers, and ethnographers interested in the most recent of the four basic geological periods – and the papers presented to the conference all concerned a single theme: the Bering land bridge. Although Christopher Columbus famously ‘discovered’ America in 1492, and whether or not you accept that he was beaten to it by the Vikings in the Middle Ages – as many scholars believe – equally clearly there were ‘native’ populations throughout the New World who had arrived there thousands of years before. Around 1959, as we have seen, palaeontologists were beginning to accept the view that
Homo sapiens
had evolved first hundreds of thousands of years ago in the Rift Valley of East Africa. Work on tectonic plates had shown that this valley was the edge of just such a plate, perhaps accounting, for some unknown reason, for why mankind should have emerged there. Since that time, unless man evolved separately in different parts of the world, he must have spread out across the earth in an order that, in theory at least, can be followed. The farthest large pieces of land from East Africa are Australia, Antarctica, and the Americas. To get to the Americas, early man would either have had to navigate huge distances across the oceans, in enough boats to create the numbers needed for propagation at the destination (which they could not have known about in advance), or crossed the narrow (56-mile) gap between Siberia and Alaska. It was this possibility that the Stanford conference was called to consider.
    The idea was not new, but the conference was presented with archaeological and geological evidence that for the first time fleshed out a hitherto vague picture. It appeared that man crossed the land bridge in three waves, the first two being between 40,000 and 20,000 years ago, and the third between 13,000 and 12,000 years ago. 8 The basic long-term context of the migrations was determined by the ice ages, which locked enormous amounts of water in the glaciers at the poles, reducing sea levels by up to a hundred metres, more than 300 feet (the Bering Straits are 24 fathoms deep, or nearly 150 feet). The idea of three migrations came initially from an analysis of artefacts and burial techniques, later from an analysis of art, language, and genes. Calculations by C. Vance Haynes in Denver, made the year after the