From one continent to six: 200 – 20 million years ago
First south America splits from Africa and drifts westwards (it is the snug fit between their coast lines which suggests the idea of continental drift to Alfred Wegener in 1912). Then Antarctica, India and Australia separate from Africa. Antarctica moves to the south, while India and Australia drift north and east.
Africa and India move slowly but forcefully towards Europe and Asia, reducing the Tethys Sea to its present-day remnant (the Mediterranean) and throwing up the Alps and the Himalayas from the force of the collision.
Finally north America splits from Europe and Asia (though remaining almost linked at its northern tip), thus forming the Atlantic ocean and completing the disposition of the continents as we know them.
Temporary bridges: 60,000 – 10,000 years ago
The ice ages play an essential part in mankind’s advance from Asia into both Australia and America. The effect of an ice age is to lower the sea level by 100 metres and more. This narrows the gaps between many islands and sometimes even exposes a complete land ridge.
One such sunken ridge is the Sahul Shelf, under the largest stretch of sea between the Indonesian islands and Australia. Another lies between Siberia and Alaska.
The first Americans: 30,000 – 5000 years ago
During the most recent Ice Age, lasting from 30,000 to 10,000 years ago, an undersea ridge between Siberia and Alaska emerges from the sea. Known as the Bering Land Bridge, it lies partly south of the ice cap. It develops a steppe-like ecology of grasslands, grazed by large animals such as horses, reindeer and even mammoth.
Gradually, in many separate incursions, the hunter-gatherers of the Siberian steppes pursue their prey across the land bridge and into America. When the melting ice submerges the bridge, about 10,000 years ago, these northeast Asians become isolated as the aboriginal Americans.
The Siberian hunter-gatherers probably make their way south along the north coast of Alaska and down through the valley of the Mackenzie river. Archaeological evidence shows that by about 15,000 years ago the central plains of America are widely inhabited. Traces of human activity at this time are preserved in the remarkable La Brea tar pit in Los Angeles. The glacial conditions further north mean that the plains are at this time cool and moist.
During the next 5000 years, while the glacial period continues, humans penetrate as far as the southern tip of South America.
The retreat of the ice caps, beginning about 10,000 years ago, makes northern regions increasingly habitable both for large animals and for the humans who prey on them. By 8000 years ago hunter-gatherers have moved up the eastern side of the continent into Newfoundland and the prairie provinces of Canada.
From about 7000 years ago human groups adapt to the conditions of the northern coast of Canada, living mainly as hunters of sea mammals. They spread gradually eastwards along the edge of the Arctic Circle, eventually reaching Greenland. These hardiest of all human settlers survive today as the Eskimo (or, in their own name for themselves, inuit – meaning simply ‘the people’).
The first American farmers: 5000 – 2500 BC
The cultivation of crops in America begins in the Tehuacan valley, southeast of the present-day Mexico City. Squash and chili are the earliest plants to be grown – soon followed by corn (or maize) and then by beans and gourds.
These are all species which need to be individually planted, rather than their seeds being scattered or sown over broken ground. This is a distinction of importance in American history, for there are no animals in America at this time strong enough to pull a plough.
At first these crops merely supplement the food produced by hunting and gathering. But by 3000 BC the people of this area are settled agriculturalists. In this development they are followed by the hunter-gatherers of south America and then, considerably later, by some in the northern part of the continent.
The earliest known settled community in south America is at Huaca Prieta, at the mouth of the Chicama river in Peru. By about 2500 BC the people here have as yet no corn, but they cultivate squash, gourds and chili. They also grow cotton, from which they weave a coarse cloth.