The land bridge between England and France was eroded away to sever this connection, and this seems to have occurred in a sudden, catastrophic event. Sonar maps of the English Channel distinctly reveal an unusually straight and wide valley on the seafloor,62 containing streamlined islands and long, kilometre-wide eroded grooves – clear signs of a huge flood of water coursing over the ground.
As we have seen, during our current era of pulsating ice ages, glaciations have caused the global sea levels to drop over 100 metres. This allowed the shallow continental shelf around the North Sea and the Channel basin to emerge as dry land. During the ice age around 425,000 years ago (five ice ages before the most recent glaciation) a vast lake of water became trapped between the Scottish and Scandinavian ice sheets and the 30-kilometre-wide ridge of rock then still linking England and France. This lake was filled with meltwater from the ice sheets as well as the discharge from rivers like the Thames and Rhine. And with no outlet to escape through, the water rose and rose, until inevitably it began to spill over the top of the land bridge. These colossal waterfalls scooped out vast plunge pools on the channel floor and gouged backwards through the barrier until this natural dam collapsed. The entire trapped lake emptied itself as a catastrophic megaflood, widening the gaping breach in the barrier and carving the landforms on the floor of the Channel we can see with sonar today. This first megaflood 425,000 years ago is thought to have been followed by a second event around 200,000 years ago, and between them they wore away what is now the Strait of Dover, leaving the white cliffs as the stump of the former isthmus. With the subsequent thawing after each ice age and the rise in sea levels during interglacial periods, this passage formed the English Channel (or La Manche, as the French would have it).63
Britain had become permanently cut off from Europe.
The formation of the English Channel has had profound ramifications through history for Britain, as well as for Europe as a whole. The Channel has served as a natural defensive moat, protecting Britain throughout European history. The last full-scale invasion, the Norman Conquest of 1066, occurred almost a thousand years ago. Britain was close enough to trade and remain intimately involved in the politics of the Continent, but shielded at the same time.
Throughout the constant squabbling, conflicts and shifting borders of continental Europe, Britain has largely escaped the ravages of war on its own home soils and been able to remain distant and insulated, only choosing to intervene when it was in its interests.64 In the seventeenth century, for instance, it was spared the devastation of the Thirty Years War, which began as a conflict between Catholic and Protestant European states and ravaged much of Central Europe, causing huge population losses – over 50 per cent in some regions – from the resultant famines and disease. Safe behind its natural moat, Britain’s situation contrasts in many ways with that of Germany, bounded to the north by sea and to the south by the Alps, but open on both sides through the European Plain. It is this vulnerability from the lack of natural defences that explains much of the insecurity and military ambitions of the states in this region – the Holy Roman Empire, Prussia, and then Germany as a unified nation.
With clearly defined natural boundaries, and a relatively small extent, England achieved the early unification of feudal fiefdoms into a national identity.65 It has also been argued that it was this reduced threat of invasion and sense of security from external threats that allowed the progressive dispersion of power away from the autocratic monarch to a more balanced democratic system, beginning with Magna Carta in 1215 and leading to the parliamentary system in place today.66
What’s more, with no land border to defend, Britain’s military expenditure needed to be only a fraction of that of its continental rivals.67 Britain was instead able to focus its energies on building up and maintaining the Royal Navy, not just for defending the homeland – the defeat of the combined French and Spanish fleets at the Battle of Trafalgar in 1805 that sank Napoleon’s hopes of invading Britain is the most striking example – but also to guard its overseas colonies and protect its commercial interests and trade routes, as it developed a seaborne empire that came to supersede those of the Spanish, French and Dutch.
Of course, it’s impossible to say with any certainty how European history might have played out had Britain not been an island. What might have happened if the Scottish and Scandinavian ice sheets had never merged to trap the glacial lake that disgorged through the Channel, eroding away the isthmus and opening the Strait of Dover? What if the ice ages had been a little less icy? This is not the place for speculating on counterfactual histories, but thinking about the potentially profound alternative outcomes underscores the importance of geology in how we find the world today. If Britain were still linked to the continent by a land bridge, would the blitzkrieg sweep of the Wehrmacht across Europe also have defeated this last bastion of resistance against Nazi Germany? Would Britain have fallen to Napoleon’s Grande Armée in 1805, or would Spanish forces have invaded in 1588 (without the need for an armada)?
It could be argued that the strong island nation has helped maintain a power balance in the Continent’s history by resisting invasion and preventing any one power from consolidating a European empire. On the other hand, its geographical isolation has created an island mentality that made Britain often stand aloof and reluctant to enter into closer relationships with its Continental neighbours, despite common interests and a shared fate.
Thus the most recent period of our planet’s history has allowed our species to spread around the entire globe, and the lasting impressions the pulsing ice ages left on the landscape have had profound implications for the course of human history. The entire story of civilisation has played out during the current interglacial period, and we will now turn our attention to the planetary forces lying behind this fundamental transition in the human story: the domestication of wild plant and animal species and the emergence of agriculture.
Chapter 3
Our Biological Bounty
Between 20,000 and 15,000 years ago the overlapping rhythms of the Milankovitch cycles started warming the Northern Hemisphere once again. The great ice sheets began to thaw and recede, and the deep freeze of the last ice age drew to a close.1 In North America, much of the run-off water from the melting ice sheets became trapped behind a ridge of debris deposited at the base of the retreating glaciers. This formed immense meltwater lakes, the largest of which has been named Lake Agassiz after the Swiss-American geologist who first proposed the (at the time) radical notion of a past ice age smothering the Northern Hemisphere. By 11,000 BC Lake Agassiz had expanded to cover almost half a million square kilometres of Canada and the northern United States – an area about the size of the Black Sea. Then, the inevitable happened. The natural dam burst and the huge volume of glacial water disgorged in an immense, surging flood. It ran through the Northwest Territories along the current course of the Mackenzie River and into the Arctic Ocean.2 This sudden release of the trapped water caused an immediate jump in global sea levels. But it was the effects it had on a culture developing some 10,000 kilometres away in the eastern Mediterranean region of the Levant that were far more profound.fn1
PARADISE FOUND AND LOST
Whilst the ice sheets were retreating, forests expanded again to replace the wide bands of arid steppes and scrubland, rivers swelled and deserts shrank. With the warmer, wetter conditions, lush vegetation proliferated and populations of grazing mammals increased.4 Springtime was returning to the planet, and our hunter-gatherer ancestors found the going much easier. In the Levant, the land flushed with wild wheat, rye and barley, and recovering woodland. Here a people known as the Natufians emerged, who appear to have formed the first sedentary society in the world, even before the development of agriculture. They settled in villages of stone and wood, gathering the wild cereals along with fruit and nuts from the woodland, and hunting gazelle.5 If ever there were a hunter-gatherer Garden of Eden, it would have been here.
This golden era did
n’t last long, however. About 13,000 years ago a sharp climatic jolt, lasting over 1,000 years, struck this region of the Near East and the Northern Hemisphere as a whole. This is known as the Younger Dryas event, and it saw a rapid regression of climate, which over the course of just a few decades returned towards a much colder and drier state. And the cause for this abrupt yank back to ice age conditions is thought to have been the disgorging of Lake Agassiz.
The sudden drainage of this vast lake placed a lid of freshwater on the northern Atlantic, which temporarily shut down the pattern of ocean circulation. Today, the world’s oceans operate vigorous conveyor belts of cycling waters that transport heat from the equator towards the poles. This is known as the thermohaline circulation, as it is driven by differences in the temperature and salinity of the seawater. Winds blow the warm surface waters from the planet’s midriff towards higher latitudes – we’ll return to this in Chapter 8 – sustaining the Gulf Stream, for example, that delivers Caribbean warmth and moisture to Northern Europe. Evaporation along the way turns the seawater more salty, and it also cools on its journey north. Both these effects make the water more dense, so that near the poles it sinks to the ocean floor, and returns towards the equator at depth. The sinking of polar water also draws in more water behind it to maintain the current. But the rapid dumping of a huge amount of freshwater into the North Atlantic from the discharge of Lake Agassiz abruptly stalled the salinity pump of this conveyor belt. The shutting down of the ocean circulation system, which was redistributing heat from the equator, shunted much of the Northern Hemisphere back to the conditions experienced during the height of the Ice Age.6
For the Natufians, the environmental crisis of plunging temperatures and declining rainfall saw their homelands reverting to arid, treeless steppes of thorny shrubs, and the abundant wild food sources dwindled before their eyes. It seems that at least some of the Natufians responded by abandoning their fledgling sedentary lifestyle and returning to migratory foraging. But some archaeologists believe that this Younger Dryas event spurred others to turn from their hunter-gatherer ways and instead develop agriculture. Rather than roaming further and further to collect enough food to survive, they brought seeds home and planted them in the ground – the first step of domestication. Plump rye seeds found in the archaeological remains of Natufian villages have been interpreted as signs of this development. The claim is controversial, but if this was the case it would make the Natufians the first farmers in the world. An invention that would for ever change the way we live was born out of the hardship of sudden climate change.7
Prompted by a particular chain of planetary events – the disgorging of Lake Agassiz, the stalling of the Atlantic circulation system, and the jolt of the Younger Dryas event – the Natufians may have been the first seed-sowers, but they were already a settled culture, and so perhaps uniquely set up to try this earliest experiment with farming. Yet within a few millennia, as the planet warmed after the last ice age, people around the world came to follow. Between about 11,000 and 5,000 years ago agriculture developed in at least seven different places across the Earth.
THE NEOLITHIC REVOLUTION
While anatomically modern humans had appeared in Africa by around 200,000 years ago, our ancestors only became behaviourally modern between 100,000 and 50,000 years ago. They now possessed the same linguistic and cognitive faculties that we have today, lived in social groups, and crafted and used tools and fire proficiently. They carefully buried their dead, made clothes, and produced expressive artwork in which they portrayed themselves and the natural world around them in cave paintings and bone and stone sculptures. They were adept hunters, they fished, and they gathered a wide variety of edible plants. They had even begun to grind wild grain into flour on simple millstones.8
As we saw in the last chapter, from about 60,000 years ago humanity migrated out of Africa and dispersed around the entire globe. But it wasn’t until around 11,000 years ago that the first enduring steps towards agriculture and settlement were taken, a transition known as the Neolithic Revolution. The North American ice sheet, though quickly shrinking, still covered more than half of Canada when the first crops were being domesticated in the Fertile Crescent in the eastern Mediterranean, and then shortly afterwards in the Yellow River valley in northern China.9 Within just a few thousand years our ancestors in several other regions of the world were doing the same. Agriculture also emerged in the Sahel band of North Africa, the lowlands of Mesoamerica, the Andes–Amazon region of South America, the woodlands of eastern North America, and New Guinea.10 After living 100,000 years through the last ice age as hunter-gatherers, with the warming of the world different peoples around the planet started down the road of agriculture and civilisation that transformed our species for ever.
It’s almost as if a starting gun had gone off. What were the planetary forces behind this defining step of human existence?
We can’t be certain why people in different places around the world first turned their hand to deliberately sowing seeds and carefully tending plants, beginning the process of domestication and selective breeding of crops. The development of agriculture may have been spurred by a spell of favourable climate that made attempts at farming less risky and more inviting, or conversely by a sudden regional shock of deteriorating conditions – like the the Younger Dryas event – that prompted a settled community to find different ways of feeding itself.11 But either way the end of the last ice age was clearly instrumental.
The fact that humanity didn’t settle down to begin cultivating the land during the Ice Age is perhaps not surprising, although the reason isn’t so much the cold conditions. While the northern ice sheets extended far down from the Arctic to smother much of the high latitudes of America, Europe and Asia, conditions were not impossibly cold elsewhere. The temperature around the tropics was only a degree or two cooler than today. And although the Ice Age Earth, as we’ve seen, was on the whole drier, it was not so arid everywhere as to prevent the development of agriculture.12 The limiting factor was probably not that the climate was inimically cold or dry, but that it was extremely variable. Regional climate and rainfall could shift suddenly and dramatically.13 Any Ice Age tribes that attempted precocious experiments with cultivation are likely to have had their efforts snuffed out by just such a rapid fluctuation. Even later in our history, well-established civilisations have collapsed when their regional climate dried out and crippled their agricultural support, such as the Harappans in India, the Old Kingdom in Egypt, and the classical Maya.14 fn2
Interglacial periods, such as the one we’re living in right now, on the other hand, are marked by their comparatively steady climatic conditions. Indeed, the last 11,000 years of the current Holocene interglacial have been the longest stable warm period of the past half-million years.16 And the rise in atmospheric carbon dioxide after the last ice age, which would have invigorated plant growth, was a global effect and so may explain why cultures around the world developed agriculture almost simultaneously.17 Such stable, warm and wet conditions in regions that reliably produced large-grained grasses would have motivated people to tend a few select species themselves and settle down rather than roam more widely. It seems as though interglacial periods are a prerequisite for farmers.
Let’s look in detail now at how we domesticated wild plants and animals, and what determined which species became adopted by humanity.
SEEDS OF CHANGE
The Holocene is the first interglacial period that modern humans have experienced, and almost immediately after it began peoples around the world started developing agriculture. Wheat and barley were first domesticated around 11,000 years ago in the rain-watered, hilly landscape of southern Turkey and then were spread to the plains between the Tigris and Euphrates,18 a region called Mesopotamia – ‘the land between the rivers’.19 Irrigation was first developed in the Turkish highlands a couple of thousand years later, and then adopted in Mesopotamia 7,300–5,700 years ago to control and distribute the floodwaters of
the two rivers.20 The region curving between Mesopotamia, the Levant and the River Nile is known as the Fertile Crescent: an arc of cultivable land within the otherwise arid environment of North Africa and the Middle East.
In China, millet was cultivated from around 9,500 years ago in the cooler, and seasonally drier, valleys of the Yellow River in the north-west. This millet, and then the soya bean that was domesticated around 8,000 years ago, were grown in the soft, fertile loess soils of the region.21 Around the same time, rice cultivation began along the Yangtze river in the warmer and wetter tropical region of southern China.22 Here huge amounts of rice came to be grown in paddy fields and carefully constructed terraces on hillsides, which demanded skilful water engineering to create ponds only a few inches deep in each paddy field that could be drained before harvest.23
The crops domesticated in the Fertile Crescent spread to the Indus Valley around 9,000–8,000 years ago, and rice cultivation started in the Ganges Delta, possibly domesticated independently of that in China.24 In the Sahel, the band of semi-arid climate between the Sahara Desert and the savannah further to the south, the cultivation of sorghum and African rice began around 5,000 years ago, before the continued drying out of the region forced farming communities to migrate to the more humid regions of West Africa.25
In the Americas, squash plants were domesticated in Mesoamerica around 10,000 years ago, and maize (corn) was grown in southern Mexico from 9000 years ago; later, beans and tomatoes also became staple crops here.26 The potato was cultivated in a large number of varieties in the Andes from about 7,000 years ago.27 In the highlands of tropical New Guinea, the starchy tubers of yam and taro were cultivated between 7,000 and 4,000 years ago.28 fn3
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