HUMANPAST.NET

Environment                  4,000 BC
Africa
Southwest Asia
Egypt
Indus Valley
China
Europe
South America
Mesoamerica
North America
Other

In General

 Starting with the broad features of the Holocene, the global climate reached an optimum around 6 kya. Just how benign the climate became can be judged by the expansion of forests to high latitudes of the northern hemisphere. They reached their limits across Eurasia around 7 kya, some 200 to 300km farther north than their current extent. In northern Canada this expansion was delayed a further two to three thousand years by the slower collapse of the Laurentide ice sheet, which did not completely disappear until around 6 kya, when the post-glacial warming reached its peak. On the evidence of tree cover the average summer temperature in mid­latitudes of the northern hemisphere was 2 to 3°C warmer than it is today. Not only had trees spread farther north than now but they also extended higher into upland areas... (145)

Africa

Rock art dating to 5000 BC corroborates what the radar equipment revealed. In Libya, Egypt, and Mali, petroglyphs depict not only grazing animals, but also aquatic life such as crocodiles. This indicates that the desert was inhabited during a time prior to 4000 BC and as far back as 8000 BC, when the climate was wet. (70)

The climatic record is, however, unequivocal: for most of the time between around 14 kya and 5 kya the Sahara experienced a monsoonal climate. The region had considerably greater rainfall than now and much of the land had permanent vegetation. (145)

Southwest Asia

Between about 5500 and 3500 B.C. Mesopotamian climates were comparatively humid, with a change to cooler and drier conditions after about 3500 BC. Subtle changes in climate like this might have had major effects on the settlement history of the area, because the zones in which dry-field rainfall-base grain cultivation was possible may have shifted. (46)

Between 13,000 BC and 4000 BC sea levels rose significantly as ice sheets melted. Meteorologists suggest that there was increased rainfall in the Near East in this era and botanists point to increased plant life. (68)

In the 1990s Kurt Lambeck of the Australian National University carried out a detailed study of the Persian Gulf in order to map and simulate its 'palaeo-shorelines' from 18,000 years ago - around the end of the Last Glacial Maximum -right up to today. He calculates that the modern shoreline of the region was reached shortly before 6000 years ago, and exceeded as relative sea-level rose 1-2 metres above its present level, inundating the low-lying areas of lower Mesopotamia. This marine transgression, which occurred between approximately 6000 and 5500 years ago, flooded the coastal plains of Sumer and extended the northwestern shoreline of the Gulf to the doorsteps of Eridu and Ur - where the rising waters may have temporarily peaked as high as 3 metres above today's level before receding. (124)

In his important book Eden in the East Oppenheimer argues that what happened in the Gulf at this time, between approximately 6000 and 5500 years ago (4000-3500 BC), was the local effect of a worldwide episode of rapid, relatively short-term flooding known as the Flandrian transgression - which had a significant impact not only along the shores of the Gulf but in many other parts of Asia as well. Noting that 'the destructive effect of the Flandrian transgression in wiping out coastal archaeological sites up to about 5500 years ago is now well recognized,’ he launches the interesting speculation that in the case of Sumer: Eridu may be the oldest coastal city not destroyed by the invading sea. In other words it could have been the last old city to be built at the post-glacial high water point. (124)

The steadily rising sea levels might have had a more profound effect on coastal communities where large areas were inundated in fits and starts. For example, this could have happened in the Persian Gulf. This enclosed sea goes no deeper than 100 m, and much of the seabed is only about 40 m below the present-day surface. When sea levels were 120 m lower the gulf would have been dry land 20 kya, and the ancestral river system of the Tigris and Euphrates flowed through the deepest part of the gulf, a canyon cut by the river waters to the Indian Ocean. The postglacial rise in sea level inundated the floor of the gulf between 15 and 6 kya. The sea advanced more than 1000 km, forcing any people living there to abandon their settlements. (145)

The climatic record is, however, unequivocal: for most of the time between around 14 kya and 5 kya the Sahara experienced a monsoonal climate. The region had considerably greater rainfall than now and much of the land had permanent vegetation. (145)

Covering an area of some 30000 km, the flat, river-made land of Sumer had no minerals, almost no stone and no trees. In summer the daytime maximum temperatures average around 40°C and often reach 5O°C. Annual rainfall is about 150mm and it is bone dry for eight months of the year. Winter nights are cold, and the strong north winds can bring squally rainstorms. In spring, the melting snows of the Taurus and Zagros mountains produce flash floods. In bad years, these swept everything before them. While the climate of the mid-Holocene may have been moister, these fundamental climatic challenges were part of the development of the region. Yet by around 5.8 kya as many as 10,000 people may have lived in the city of Uruk. (145)

c. 5000-4000 BC A 'second' flood strikes the Mesopotamian plains in the form of a series of localized inundations. The memory of these events is confused with much earlier traditions concerning a deluge accompanying the cessation of the last Ice Age, c. 9500 - 9000 BC. They are remembered as the 'Flood of Noah' by the Yezidis of Kurdistan. (149)

Egypt

Although there have been major fluctuations in the annual volume of the Nile--for example, catastrophically low water levels in some of the years between 2250 and 1950 B.C.--the Nile floodplain has existed in essentially its present form since about 3800 BC. In ancient times, however, the Mediterranean coastline was farther inland because the Delta had not sunk nearly as far as it has now under the weight of accumulated silt.

The annual floods were usually visible in southern Egypt, near the Nubian border, by late May, and the river rose quickly thereafter, until the beginning of September, when it began a long slow recession to its lowest level the next May. The Egyptian annual calendar was based on this flood cycle, dividing the year into three periods of four months each. (47)

As the climate grew more humid around 8000 BC, rainfall turned low-lying areas into lakes and playas. With the onset of this "Neolithic pluvial," the region we now know as Egypt became an extension of the Sahelian savanna. The area offered pastoralists and animals new habitable lands. According to Haynes, during that time, the area received a minimum of eleven inches of rainfall annually and possibly as much as twenty-four. Between 7000 and 4000 BC, when the leading edge of monsoon rains covered a significant portion of Africa's interior, a "pluvial maximum"--when rainfall was at its peak--developed, turning the desert green with life. (70)

Several wadis flowed into the Nile, including the Wadi Howar, across north-central Sudan, and the Wadi Melik, which flowed from 5700 to 4000 BC. Humid conditions along the Nile Valley resulted in deposits of silt, mud, and gravel before 3000 BC. Nile flooding between 6200 and 4600 BC created high lake levels in El Faiyum, a province in Upper Egypt, and discharged a considerable amount of freshwater into the Mediterranean Sea. (70)

Fossil shells of the large land snail, found in stage 3 surface soils in northwestern Sudan, provide evidence of at least twelve inches of annual precipitation during the late stage of this Neolithic Pluvial. Radiocarbon ages determined on the organic fraction of the snail shells range from 4500 BC at the north end of the study area, to later than 1100 BC at the south end, indicative of a retreating forest-savanna during the final stages of the pluvial period in northwestern Sudan. (70)

The Nile flowed at high stage through 4600 BC, but was lower with only occasional high stages thereafter. Intermittent floods and low flow stages resulted in the deposition of sediments, oxidized layers, and calcareous "oozes" along the Nile cone (the area of Mediterranean Sea at the river's mouth). After 4500 BC lake levels in Faiyum dropped fifty feet, surged to higher levels around 3800-3700 BC, and waned again from 3700 to 1700 BC. Along the Nile's higher reaches, tributaries stopped flowing altogether around the fifth millennium BC. The Wadi Melik ran dry around 4000 BC. Flows from Wadi Howar diminished significantly. Areas west of the Nile Valley and the Faiyum region are generally recognized as arid from 5000 to 4500 BC. After 4500 BC, savanna flora diminished, allowing Saharan elements to dominate. By 4000 BC, a full desert flora was in place in most areas of southern Egypt, excluding some oases, wadis, and the region of the Gilf Kebir. Through 3000 BC, water was still seasonally available, allowing the growth of rich vegetation, comparable to the modern gallery forests of Tibesti and Hoggar. (70)

Investigations at Selima suggest that the lake endured intense evaporation between 5000 and 4000 BC, resulting in the formation of a saltwater lake around 4400 BC. Plant life, established in the region, persisted until 4000 BC. Isotopic measurements on mollusks indicate that dry conditions prevailed around 3600 BC. (70)

By 5000 BC, many rain-fed playas in Egypt had vanished. Most were significantly desiccated, due to drought, by 3500 BC, and plant life began to disappear as early as 5600 BC. After 3900 BC, many playa basins were literally filled with sand. At Nabta Playa alternating layers of forest and windblown sands indicate that arid periods interrupted more humid conditions between 5700 and 3800 BC. (70)

Egypt's Arba'in Desert and surrounding region has been arid, receiving less than half an inch of rain per year for the last fifteen thousand to twenty thousand years. However wetter conditions prevailed between 7000 and 4000 B.C.E., with rainwater averaging more than twelve inches per year and possibly as much as twenty-four. (70)

Rock art dating to 5000 BC corroborates what the radar equipment revealed. In Libya, Egypt, and Mali, petroglyphs depict not only grazing animals, but also aquatic life such as crocodiles. This indicates that the desert was inhabited during a time prior to 4000 BC and as far back as 8000 BC, when the climate was wet. (70)

The climatic record is, however, unequivocal: for most of the time between around 14 kya and 5 kya the Sahara experienced a monsoonal climate. The region had considerably greater rainfall than now and much of the land had permanent vegetation. (145)

Indus Valley

 

China

 

Europe

 In 1931 a trawler working in the southern North Sea dredged up a lump of peat containing an exquisitely crafted spearhead made from a deer's antler. Dated as being nearly 14 kyr old, this artefact was dramatic evidence of how early humans exploited the broad expanses of land that had been exposed during the last ice age, and were only reclaimed by the sea some 7 kya. When this spearhead was buried, dense oak forests had yet to spread into the region, known to archaeologists as 'Doggerland', where now the sea is over 30m deep. This famous find emphasises that the rise in sea level between about 15 and 5 kya covered up large areas of habitable land that had been exploited by humans and made movement around the continental margins easier. (145)

Pollen data from across Europe suggests that, around 6 kya, winters were 1 to 3°C warmer than during the twentieth century in the far north and northeast of Europe, but 2 to 4°C cooler in the Mediterranean region. At the same time, summers were warmer then in northwest Europe and in the Alps, but cooler than present at lower elevations in southern Europe. Possibly more important, summers were drier in northwest Europe and the Alps, but moister in southern and eastern Europe. This is consistent with the conclusion that the climatic patterns in mid-latitudes of the northern hemisphere at this time - identified as the Atlantic period - featured stronger westerlies. This pattern coincides with the positive phase of the NAO that, in particular, produces cooler wetter winters in the Middle East. (145)

South America

...an extremely dry period took place' between 5,000 and 6,000 years ago, "during which Titicaca fell some 250 feet below its present-day level." (69)

Mesoamerica

 

North America

 ...aboriginal Americans were probably directly affected by a number of climate fluctuations, such as the Hypsithermal (c. 4000 BC), when climates seem to have been cooler and moister.

In some prehistoric periods the Southwest was wetter than it is today, but for most of the last ten thousand years the Southwest has usually been at least as hot and dry as it is today, and there were short periods of extreme drought. (53)

Other

 …until as recently as 6000 years ago, as I was to discover when I received Glenn Milne's inundation maps for the region in the summer of 2001, Bimini remained part of a large antediluvian island lying across the Gulf Stream from Florida. Very close to the north-western tip of this palaeo-island, overlooking the Gulf Stream then as they do today, were what is now Paradise Point and the present site of the Bimini Road. (124)

The inundation map for 12,400 years ago shows, to the north, a crescent-shaped island around present-day Grand Bahama, Great Abaco and Little Abaco. Clockwise to the south-east from there we come to a second lost island. This island fills in what is now Tarpum Bay under Eleuthera, then connects via the thin but very probably unbroken line of the Exuma Cays to an even larger exposed area stretching almost as far south as Cuba - itself significantly larger than it is today. Third, to the north-west in the direction of the Florida peninsula covering present-day Andros island and occupying most of the Great Bahama Bank, is the largest antediluvian island of all, with Bimini and the Bimini Road right at its tip.

The inundation map for 6900 years ago shows some coastal erosion of the three main islands but otherwise the picture remains basically unchanged - indicating that the islands survived beyond the last of the three great episodes of global postglacial flooding around 7000 years ago.

However, in the next inundation map in the sequence, for 4800 years ago, all the islands have gone. The most likely culprit for their inundation is the so-called Flandrian transgression, the final spasm of the Ice Age meltdown, which took place between 6000 and 5000 years ago. (124)

The same story of pressure on resources emerges from analysis of rock art in northern Australia. This tells a tale of continuing collective violence, which develops from individual and small group conflicts around 10 kya to larger group confrontations from about 6 kya. This covers a period of ecological crisis when the rising sea flooded the rich plains between Australia and New Guinea. (145)

All around the world there is also overwhelming evidence to show that, while the old ice-caps were melting, new ones were taking their place. The continent of Antarctica, for instance, began its gradual glaciation towards the end of the last Ice Age and was still relatively free of ice in certain regions right down until 4000 BC. Other evidence indicates that a short relapse, a kind of mini-ice age, where the ice sheets began advancing once more, occurred in Europe and Asia Minor sometime between 11,000 to 10,000 years ago. More curious is evidence from locations as far apart as northern Armenia and the Andean Altiplano of Bolivia and Peru, not only of the extinction of animals during the eleventh and tenth millennia BC, but also of dramatic elevations in the terrain's altitude above sea level. (149)

Using the ionium-dating method, researchers at the Carnegie Institute in Washington DC were able to establish beyond any reasonable doubt that great rivers carrying fine- grained well-assorted sediments had indeed flowed in Antarctica until about 6000 years ago, as the Oronteus Finaeus Map showed. It was only after that date, around 4000 BC, 'that the glacial kind of sediment began to be deposited on the Ross Sea bottom...The cores indicate that warm conditions had prevailed for a long period before that. (152)

Some 260 million years ago, during the Permian period, deciduous trees adapted to a warm climate grew in Antarctica. ...Here at the southernmost known mountain in the world, - scarcely two hundred miles from the South Pole, was found conclusive evidence that the climate of Antarctica was once temperate or even sub-tropical. ...sedimentary cores collected from the bottom of the Ross Sea by one of the Byrd Antarctic Expeditions provide conclusive evidence that 'great rivers, carrying down fine well grained sediments' did flow in this part of Antarctica until perhaps as late as 4000 BC. From 6000 to 15,000 years ago the sediment is fine-grained with the exception of one granule at about 12,000 years ago. This suggests an absence of ice from the area during that period, except perhaps for a stray iceberg 12,000 years ago. ...at one time the temperatures of the Arctic Ocean were similar to the contemporary temperatures of the Bay of Bengal or the Caribbean Sea. (152)