The Holocene Climate Events That Shaped Prehistory and Ancient History

There is considerable evidence to support environmental determinism as a key lens through which to understand human history and human prehistory.  This is the view that large scale climate events have been major drivers of cultural transitions, technological innovation and cultural change in modern human prehistory.

In the period from ca. 8000 BCE when the first farmers and herders domesticated crops and animals in the Fertile Crescent, an event known as the Fertile Crescent Neolithic Revolution, until ancient Greco-Roman times which are well documented historically, there have been three such events: the 8.2 kiloyear event, the 5.9 kiloyear event and the 4.1 kiloyear event, and possibly a less severe one as well which helped to precipitate the historical events known as Bronze Age Collapse about 3.2 thousand years ago.  This recap can be read together with a post of about a year and a half ago on a similar topic, but with a greater focus on showing connections to a larger number of historical events.

It takes an artists interpretation to really get a grip on the immensity some of the key pre-Neolithic climate events like the Last Glacial Maximum ca. 20,000 years ago.  Similarly notable pre-Neolithic climate events include: the climate impact of the Toba eruption on Africa (a map of Toba ashfall is here), the cause of the Younger Dryas, and the Middle Stone Age Paleoclimate.  I also have a post on Arabic Paleoclimate which is highly relevant to Out of Africa and beyond scenarios and Neanderthal admixture.

The 8.2 kiloyear event, the first wave of the European Neolithic and Chadic ethnogenesis

The Fertile Crescent Neolithic expanded to the Indus River Valley, to Egypt, and to the parts of the Balkans adjacent to Anatolia, about a thousand years after it arose in the core Fertile Crescent region, in each case, before the 8.2 kiloyear event.  But, this event appears to have bottled up further Neolithic expansion until it ended, at which point the first farmers of Europe started to arrive, particularly in Southern Europe and in the Danube River basin.

This first wave of the European Neolithic revolution in which the first farmers and herders expanded into Europe is mostly associated with the LBK culture in Eastern and Central Europe (ca. 5500 BCE to 4900 BCE) and the roughly contemporaneous Cardial Pottery culture in Southern Europe. This took place in the period of restored positive climate conditions immediately following the 8.2 kiloyear event.

The 8.2 kiloyear event is the term that climatologists have adopted for a sudden decrease in global temperatures that occurred approximately 8,200 years before the present, or c. 6,200 BCE, and which lasted for the next two to four centuries. Milder than the Younger Dryas cold spell that preceded it, but more severe than the Little Ice Age that would follow, the 8.2 kiloyear cooling was a significant exception to general trends of the Holocene climatic optimum. . . .

The 8.2 Ka cooling event may have been caused by a large meltwater pulse from the final collapse of the Laurentide ice sheet of northeastern North America—most likely when the glacial lakes Ojibway and Agassiz suddenly drained into the North Atlantic Ocean. . . . causing significant circum-North Atlantic cooling. Estimates of the cooling vary and depend somewhat on the interpretation of the proxy data, but drops of around 1 to 5 deg C (1 to 9 deg F)have been reported. In Greenland, the event started at 8175 Before Present, and the cooling was 3.3 deg C (decadal average) in less than ~20 years, and the coldest period lasted for about 60 years, and the total duration was about 150 years. Further afield, some tropical records report a 3 deg C (5 deg F) cooling from cores drilled into an ancient coral reef in Indonesia. The event also caused a global CO2 decline of ~ 25 ppm over ~ 300 years. However, the dating and interpretation of this and other tropical sites are more ambiguous than the North Atlantic sites.

Drier conditions were notable in North Africa, while East Africa suffered five centuries of general drought. In West Asia and especially Mesopotamia, the 8.2ky event was a three-hundred year aridification and cooling episode, which may have provided the natural force for Mesopotamian irrigation agriculture and surplus production that were essential for the earliest class-formation and urban life. However multi-centennial changes around the same period are difficult to link specifically to the approximately 100-year abrupt event as recorded most clearly in the Greenland ice cores.

The initial meltwater pulse caused between 0.5 and 4 m (1 ft 8 in and 13 ft 1 in) of sea-level rise. Based on estimates of lake volume and decaying ice cap size, values of 0.4–1.2 m (1 ft 4 in–3 ft 11 in) circulate. Based on sea-level data from below modern deltas, 2–4 m (6 ft 7 in–13 ft 1 in) of near-instantaneous rise is estimated, in addition to 'normal' post-glacial sea-level rise. Meltwater pulse sea-level rise was experienced fully at great distance from the release area. Gravity and rebound effects associated with the shifting of water masses meant that the sea-level fingerprint was smaller in areas closer to the Hudson Bay. The Mississippi delta records ~20%, NW Europe records ~70% and Asia records ~105% of the global averaged amount. The cooling of the 8,200 event was a temporary feature; the sea-level rise of the meltwater pulse was permanent.

The archaeological, linguistic and genetic evidence all support the case that the linguistic group that comprises the Chadic people of the African Sahel, who have high frequencies of the genetically distinct (for Africa and for Afro-Asiatic language speakers) Y-DNA haplogroup R1b-V88 which is estimated to have arisen 7200 BCE to 3600 BCE and also have distinctive mtDNA clades with an estimated origin using more accurate, although hardly exact, mtDNA dating, of 6000 B.C.E.  More archaeological data on the African Neolithic can be found here.

The ancestors of the Chadic people probably arrived on the shores of Lake Chad to fill the vacuum created by the 8.1 kiloyear event around 5200 BCE, which is a date consistent with Y-DNA, mtDNA, archaeological dating around lack Chad and the suggestions of climate data.  A few centuries earlier as a result of the 8.1 kiloyear event, ca. 5500 BCE, Lake Chad pretty had much entirely dried up, but it would have started to fill up again by 5200 BCE (in contrast, a maximal Lake Chad is illustrated here).  This strongly supported and archaeologically grounded date is very useful in the larger scheme of historical linguistics and archaeogenetics.

First, it provides a calibration point for the time depth of one of the Afro-Asiatic languages families.  Almost everyone agrees, in part because of the genetic distinctiveness of the Chadic people relative to other Afro-Asiatic populations, that Chadic is a later branching part of the Afro-Asiatic language family.  This implies that proto-Afro-Asiatic dates to a time frame of more than 7000 years ago.

Second, it provides a time frame for one of the more notable long range folk migrations in human history, because R1b-V88 is an outlier Y-DNA clade in Africa that dd not originate there, but also does not have its origins in recent historic migrations (since there are no obvious modern R1b-V88 populations that could have provided a source for this Y-DNA clade in the Islamic era or the European colonial era).

This migration would was almost certainly after the Neolithic revolution reached Egypt (and very likely proceeded down the Nile River Basin, and then either across the southeast corner of the modern Sahara desert or up the White Nile to its source and then over the river basin divide into the Lake Chad basin.  The Chadic people would have appeared close in time to the arrival of pastoralism south of the Sahara desert.  The fact that Chadic autosomal genetics are quite similar to those of other West Africans, however, suggests that the initial Chadic migrants may have been male dominated and patrilocal, and may have absorbed African mtDNA (although one analysis found that Chadic mtDNA was closer to Afro-Asiatic populations than to other Central Africans) and autosomal genetics by taking local brides.

And, third, it provides a calibration point for other R1b clades such as R1b-M269 that can safely be presumed to be younger than the very basil R1b-V88 clade of that Y-DNA haplogroup.  This is consistent with the ancient DNA evidence that Y-DNA R1b was not present at any great frequency in first wave European Neolithic populations.

The 5.9 kiloyear event and Europe's late Neolithic or copper age demographic transition

The 5.9 kiloyear event (ca. 3900 BCE) is a plausible cause of the abrupt population genetic shift that occurred in Europe sometime between first wave Neolithic populations of the LBK and CP Neolithic, and the population genetics of Western Europe which were present at the advent in Indo-European migration into Western Europe.

The 5.9 kiloyear event was one of the most intense aridification events during the Holocene Epoch. It occurred around 3900 BC (5,900 years BP), ending the Neolithic Subpluvial and probably initiated the most recent desiccation of the Sahara desert. Thus, it also triggered worldwide migration to river valleys, such as from central North Africa to the Nile valley, which eventually led to the emergence of the first complex, highly organised, state-level societies in the 4th millennium BC. It is associated with the last round of the Sahara pump theory. . . .In the Middle East the 5.9 kiloyear event contributed to the abrupt end of the Ubaid period.

The demographic transition could be associated either with the Megalithic culture, which was in much of Atlantic Europe, the first wave Neolithic culture to arrive there, or it could be associated with the Bell Beaker culture which appears to have started to expand from a source in Southern Iberia around 2900 BCE.  Bell Beaker populations show continuity in physical anthropology with prior populations only in the Czech Republic and Northern Spain.

The earliest examples in ancient Y-DNA haplogroup R-M269, which is associated with this demographic transition, is found in two Bell Beaker men from Germany ca. 2650 BCE, and Y-DNA R-M269 had probably reached its current predominant frequencies in Western Europe by 1300 BCE.  Another ancient Y-DNA R-M269 clade individual died around 670 CE in Bavaria.

But, without Y-DNA from the Neolithic Atlantic Megalithic culture, we can't rule out the possibility that R-M269's expansion was (1) part of the the Megalithic culture, whose people were the first farmers of much of Western Europe where the Neolithic revolution arrived later than it did in Eastern Europe and Southern Europe, or (2) the Bell Beaker people who were initially physically distinct in most places where their remains have been found, but who were previously not believed to have been a major source of demographic change in the places where their culture took hold.

Climate evidence would tend to favor an Atlantic Neolithic/Megalithic demographic transition took place just in the wake of the 5.9 kiloyear event that would have depleted any earlier Mesolithic or Neolithic populations of Europe, while the Bell Beaker culture's expansion does not coincide neatly with a major climate event of the Holocene era.

Archaeological evidence also tends to favor the Atlantic Neolithic/Megalithic period as the source of this demographic transition.  A charts from Stephen Shennan et al., Regional population collapse followed initial agriculture booms in mid-Holocene Europe. Nature Communications (2013) reproduced and annotated by Maju at his blog show clearly, the volume of archaeological finds in fairly well studies Europe suggests that the Atlantic Neolithic/Megalithic period were aspects of the same historical event and that this event had a much more dramatic and far more universal than the advent of subsequent Bell Beaker and Corded Ware cultures.

On the other hand, the overall data set and most of the subregions studies show that the Atlantic Neolithic was almost universally followed by a fairly severe bust.  For example, in the time period from 3400 BCE to 2200 BCE, the people of Ireland mostly reverted from their initial farming method of subsistence to a hunting and gathering approach as their primary means of food production.  The demographic transition could represent copper age backfilling of new populations into the gap left by the first bust of the Atlantic Neolithic (in some cases all of the way down to abandoning the Neolithic revolution package of farming technologies entirely) after its initial spectacular boom that eventually substantially replaced or profoundly diluted the genetic contributions of Mesolithic forager populations in Europe to the modern gene pool.

But, if the Atlantic Megalithic culture rather than the Bell Beaker culture is the source of this demographic transition it is still necessary to determine why it is that the first farmers of the Atlantic European region were genetically distinct from the early first farmers of Eastern and Southern Europe, who were part of the LBK and CP archaeological cultures.

The absence of a meaningful proportion of Y-DNA in Western Europe ancestral to Y-DNA haplogroup R-M269 in the modern population genetics of Western Europe and in the available ancient Y-DNA of Western Europe, suggests strongly that R-M269 in Western Europe has its origins in a Neolithic or Copper Age culture that migrated to Western Europe (probably first to Iberia from which both the megalithic and Bell Beaker cultures expanded) from someplace else where Y-DNA R1b haplogroups ancestral to R-M269 are present either currently or have been found in ancient DNA.  Another recent study using a different method also discerned that Y-DNA haplogroup R-M269 has experienced an extremely rapid recent expansion.

The Civilization Destroying 4.1 Kiloyear Event

Another candidate cause for this abrupt population genetic shift (which is not mutually exclusive), would be the 4.1 kiloyear event (ca. 2100 BCE) which is the first major climate event whose effects were well documented in written records.

This event led to a temporary collapse of civilization in Old Kingdom Egypt, Mesopotamia's Akkadian Empire, and the Indus River Valley civilization in South Asia. It is likely that the pork taboo of many Semitic cultures arose during this climate event. The natural disasters that brought down Old Kingdom Egypt at this time may have been a historical source for the legendary history story of the plagues of Exodus.

The 4.2 kiloyear climate event appears to have simultaneously transformed and led to the rapid expansion of Indo-European populations from South Asia to Anatolia to Greece to the Paonian Plain to mountainous far western China. The climate event coincides with or precedes (1) the beginning of the Indo-European Hittites conquest of the non-Indo-European populations of Anatolia and the Northern Fertile Crescent including the non-Indo-European Hattic Civilization, (2) the arrival and conquest of pre-existing non-Indo-European peoples of the Aegean Sea region by Indo-European Mycenean Greeks, (3) the arrival of Sanskrit speaking Indo-Aryan peoples in the Indus River Valley, and (4) the arrival of the Indo-European Tocharian peoples in the Tarim Basin of Asia. The Tocharian migration is a few hundred years after the 4.2 kiloyear climate event and has its origins to the north of the Tarim Basin rather than the epicenter of the other Indo-European expansions of around this time, suggesting that climate change may have exiled them from their previous home until they arrived in a largely unpopulated Tarim Basin.

I suspect that much of the diversification of the Indo-European languages (apart from Tocharian) happened rapidly then, primarily as a result of substrate influences as Indo-European populations conquered linguistically diverse non-Indo-European populations in the general vicinity of a Pontic-Caspian plain homeland, which was becoming less habitable as a result of climate change.

The new Indo-European cultures in all of these regions, except the Tarim Basin which seems to have a different geographic source than the other expansions and did not involve contact with a substrate population, are accompanied by a preference for cremation over inhumation as a means of disposing of the dead. Cremation is also first observed on the Paoian Plain at around this time, presumably as part of a shared set of beliefs held by a rapidly expanding Indo-European culture.

Notably, however, consistent with the theory that they were probably not Indo-Europeans, the Bell Beaker people, who first appear in Western Europe in Southern Iberia ca. 2800 BCE, a culture that eventually expand to most of Western Europe, did not adopt cremation at this time. Instead, cremation arrived in Western Europe with the Urnfield people ca. 1300 BCE.

The 4.2 kiloyear BP aridification event was one of the most severe climatic events of the Holocene period in terms of impact on cultural upheaval. Starting in ≈2200 BC, it probably lasted the entire 22nd century BC. It is very likely to have caused the collapse of the Old Kingdom in Egypt as well as the Akkadian Empire in Mesopotamia. The drought may have also initiated southeastward habitat tracking within the Indus Valley Civilization. . . .

A phase of intense aridity in ≈4.2 ka BP is well recorded across North Africa, the Middle East, the Red Sea, the Arabian peninsula, the Indian subcontinent, and midcontinental North America. Glaciers throughout the mountain ranges of western Canada advanced at about this time. Evidence has also been found in an Italian cave flowstone, and in the Kilimanjaro Ice sheet, Andean glacier ice. The onset of the aridification in Mesopotamia near 4100 B.P also coincided with a cooling event in the North Atlantic, known as Bond event 3.

Aftermath

Ancient Egypt

In ca. 2150 BC the Old Kingdom was hit by a series of exceptionally low Nile floods, which was instrumental in the sudden collapse of centralized government in ancient Egypt. Famines, social disorder, and fragmentation during a period of approximately 40 years were followed by a phase of rehabilitation and restoration of order in various provinces. Egypt was eventually reunified within a new paradigm of kingship. The process of recovery depended on capable provincial administrators, the deployment of the idea of justice, irrigation projects, and an administrative reform.

Mesopotamia

The aridification of Mesopotamia may have been related to the onset of cooler sea surface temperatures in the North Atlantic (Bond event 3), as analysis of the modern instrumental record shows that large (50%) interannual reductions in Mesopotamian water supply result when subpolar northwest Atlantic sea surface temperatures are anomalously cool. The headwaters of the Tigris and Euphrates Rivers are fed by elevation-induced capture of winter Mediterranean rainfall.

The Akkadian Empire—which in 2300 B.C. was the second civilization to subsume independent societies into a single state (the first being ancient Egypt at around 3100 BC) —was brought low by a wide-ranging, centuries-long drought. Archaeological evidence documents widespread abandonment of the agricultural plains of northern Mesopotamia and dramatic influxes of refugees into southern Mesopotamia around 2170 BC. A 180-km-long wall, the "Repeller of the Amorites," was built across central Mesopotamia to stem nomadic incursions to the south. Around 2150 BC, the Gutian people, who originally inhabited the Zagros Mountains, defeated the demoralized Akkadian army, took Akkad, and destroyed it around 2115 BC. Widespread agricultural change in the Near East is visible at the end of the third millennium BC.

Resettlement of the northern plains by smaller, sedentary populations occurred near 1900 BC, three centuries after the collapse.

Arabian peninsula

In the Persian Gulf region, there is a sudden change in settlement pattern, style of pottery and tombs at this time. The 22nd century BC drought marks the end of the Umm al-Nar period and the change to the Wadi Suq period.

China

The drought may have caused the collapse of Neolithic Cultures around Central China during the late third millennium BC. At the same time, the middle reaches of the Yellow River saw a series of extraordinary floods. In the Yishu River Basin, the flourishing Longshan culture was hit by a cooling that made the paddies shortfall in output or even no seeds were gathered. The scarcity in natural resource led to substantial decrease in population and subsequent drop in archaeological sites. About 4000 cal. yr BP the Longshan culture was displaced by the Yueshi culture which was relatively underdeveloped, simple and unsophisticated.

In Egypt, the local, linguistically Coptic Dynasty of Pharaohs was replaced not long after the 4.1 kiloyear event with foreign Semitic Hyskos Pharaohs for a brief period, after which an indigenous Egyptian dynasty was restored to power.

Bronze Age Collapse aka the 3.2 ka climate event

The next historical period in which geographically widespread collapses of civilization and cultural shifts appear is Bronze Age Collapse ca. 1200 BCE which is manifest from at least Anatolia and the Eastern Mediterranean to Western Europe.  This too appears to have roots in a climate event, although not as severe a climate event as the 8.2 kiloyear event, 5.9 kiloyear event, and 4.1 kiloyear event.  Still, a 300 year drought of the kind apparently experienced during the Bronze Age collapse, is no small thing.

The Iron Age really takes off a few centuries after Bronze Age collapse.  This appears to be when Celtic, Italic and Germanic Indo-European languages and cultures appear on the scene in Western and Northern Europe.  The Philistines and the Jewish people arrive in the Southern Levant.  The classical Greek city-states emerge in the Aegean and Greek colonies are established in Italy and Iberia.  The city of Rome is founded.  The non-Indo-European Etruscans are simultaneously establishing themselves in Tuscany.  The second intermediary period ends in Egypt, and pagan Persian princes flourish until Alexander of the Great conquers them and Hellenizes them.

But, this late transition arising from what may have been a less severe climate event than the other discussed in this post, does not appear to have produced a dramatic population genetic transition in Western Europe.