Surviving the Glacial Maximum: 25,000-18,000 years ago
Cooling conditions that had long been developing since humans arrived in Australia suddenly and significantly intensified after 25,000 years bp to create what is recognized as the Last Glacial Maximum (LGM).
Lasting from approximately 25,000 until 18,000 years ago this period offered some of the cruellest and most confronting climate conditions to the occupants of Australia, and it is possible that the human responses to these extreme circumstances helped shape the subsequent cultural evolution of the ancestors of Aboriginal people.Mid-way through the LGM the oceans surrounding Australia reached their lowest, and coldest, levels. Sometime before 22,000 years ago the oceans dropped to a low-point of 125 metres below their present level.40 At approximately the same time sea-surface temperatures reached their lowest values
hunter-gatherers of coastal northwestern Australia', in Veth, Smith and Hiscock (eds.), Desert Peoples, pp. 177-205.
40 Yusuke Yokoyama, Patrick De Deckker, Kurt Lambeck, Paul Johnston and L. Keith Fifield, ‘Sea-level at the Last Glacial Maximum: Evidence from northwestern Australia to constrain ice volumes for oxygen isotope stage 2', Palaeogeography, Palaeoclimatology, Palaeoecology 165 (2001), 281-97; and T. J. J. Hanebuth, K. Stattegger and A. Bojanowski, ‘Termination of the Last Glacial Maximum sea-level lowstand: The Sunda-Shelf data revisited', Global and Planetary Change 66 (2009), 76-84. and on land it became exceptionally cold and dry.[594] These conditions were the peak of a long-term trend that altered the physical environment in which human occupants operated. Evaporation and windiness were greater than today, a combination that reduced surface water availability.[595] Consequently, in the LGM, landscapes surrounding the arid core of Australia dried to such an extent that they too became deserts, expanding the arid interior.
Rainfall was about half the amount received today, although water availability varied seasonally in some regions.[596] Glaciers formed in high-altitude areas, and many upland areas became extremely cold, dry and treeless.[597] The land surface of Sahul reached its maximum extent at this period, producing more continental climatic regimes and reducing rainfall from monsoons and cyclones. Because of the flattened topography of the now submerged continental shelf, islands close to the coastline would have been scarce. In summary environmental conditions rapidly became more severe than any encountered since humans had arrived in Australia.The consequences of these extreme conditions for people should not be under-estimated. Reduced vegetation cover triggered major sediment erosion. For instance, a significant phase of dune-building in the interior was initiated and aeolian dust storms were intense.[598] The drying of lakes and reduced surface water was often linked to lowered water tables and the formation of salt crusts.46 Some of these environmental changes created massive, sometimes irreversible, alterations to landscapes and to plant and animal resources found within them. Foods sometimes disappeared, as was the case when water levels in Lake Mungo and its neighbouring lakes reached a low level and/or became brackish. Rainfall was highly variable compared to earlier periods, and most likely this made it harder for foragers to predict when rainfall would fill water sources, as good rains occurred less often and more irregularly.47 The nature of extreme conditions varied geographically during the LGM, but across the continent it was generally a far more difficult environmental context for people. Archaeological research has yielded evidence of the dramatic impact of these climatic conditions on humans attempting to live in drying landscapes.
The most obvious archaeological signature of the severity of these conditions for human groups is the increased frequency with which people abandoned their lands.
This is revealed when the multiple archaeological deposits display no cultural material during the LGM, even though artefacts and food debris show humans had been resident prior to the LGM. The absence of cultural materials, revealing abandonment of the local area, was widespread across Australia at this time. Examples of abandoned localities include the Lake Eyre Basin and Strzelecki Desert, Nullarbor Plain near Allen's Cave, Central Australian Ranges near Kulpi Mara and Sandy Desert regions.48 It is difficult to quantify the extent of abandoned territory sincePress, 1986), pp. 117-47; Paul P. Hesse and Grant H. McTainsh, ‘Last Glacial Maximum to Early Holocene wind strength in the mid-latitudes of the Southern Hemisphere from aeolian dust in the Tasman Sea', Quaternary Research 52 (1999), 343-9; and G. C. Nanson, D. M. Price and S. A. Short, ‘Wetting and drying of Australia over the past 300ka', Geology 20 (1992), 791-4.
46 John W. Magee, James M. Bowler, Gifford H. Miller and D. L. G. Williams, ‘Stratigraphy, sedimentology, chronology and palaeohydrology of Quaternary lacustrine deposits at Madigan Gulf, Lake Eyre, South Australia', Palaeogeography, Palaeoclimatology, Palaeoecology 113 (1995), 3-42.
47 Lambeck, Yokoyama and Purcell, ‘Into and out of the Last Glacial Maximum'.
48 Ronald J. Lampert and Philip J. Hughes, ‘The Flinders Ranges: A Pleistocene outpost in the arid zone?', Records of the South Australian Museum 20 (1987), 29-34; Peter Hiscock, ‘Prehistoric settlement patterns and artifact manufacture at Lawn Hill, Northwest Queensland', unpublished Ph.D. thesis, University of Queensland (1988); Peter B. Thorley, ‘Pleistocene settlement in the Australian arid zone: Occupation of an inland riverine landscape in the central Australian ranges', Antiquity 72 (1998), 34-45; Peter Veth, ‘Islands in the interior: A model for the colonization of Australia's arid zone', Archaeology in Oceania 24 (1989), 81-92; and S. O'Connor, 30,000 Years of Aboriginal Occupation: Kimberley, North West Australia (Canberra: Australian National University, 1999).
evidence for abandonment of an entire region is equivocal where only one or two sites have been excavated, and only parts of those regions may have been unused during the LGM.
Nevertheless the mounting evidence indicates that large tracts of land became unoccupied.When regions were completely deserted it is likely that this was not a sudden, single event. In most instances it would have been the final outcome of a gradual succession of local abandonments as people retreated from risky landscapes. We observe this process in a number of places where a well- watered core portion of their territory, an oasis, allowed occupation to persist long enough to leave a record of the gradual abandonment of peripheral territory. The outstanding example of this process comes from the gorge systems inland from the Gulf of Carpentaria, particularly the gorges of the Lawn Hill River and its tributaries. These gorges are cut deep into limestone strata and today the rivers that flow through them, fed by the vast aquifer contained in the rock, do not rely on local rainfall and do not vary in discharge. Even during the LGM Lawn Hill River continued unabated, supporting a variety of aquatic fauna (fish, turtle, mussels, crocodiles) and fringing forests containing edible and useful plants. These gorge sites, such as Colless Creek Cave, record regular and relatively intense occupation during the LGM, as shown by the large numbers of artefacts, bones and shells left behind. This signature of intensive occupation reflects the contraction of life to the oases found within the gorges. Before and after the LGM people living in such sites were exploiting a wide range of adjacent environments, documented in the animal bones and artefacts that were brought some distance to the cave. However, during the LGM virtually all food came from animals living in the gorge, and the stone artefacts were made from nearby rocks; no food or artefacts were brought from areas away from the gorges. At that time people constricted their foraging range, avoided high- risk environments away from the oases, and concentrated on exploiting relatively reliable resources. This strategy made it possible for small groups of people to reside in the gorges, at least periodically until resources were exhausted, at which point they moved to other well-favoured gorge systems.
Without a refuge, the humans living along Lawn Hill River may not have survived the hyper-arid conditions of the LGM.Within the expanded arid zone human groups persisted in some localities and vanished in others. This mosaic of adaptation or abandonment was conditioned by a variety of factors. A single oasis or well-provided core area was often insufficient, as food would soon be exhausted in a foraging radius around permanent water, and foragers would have required a series of such patches to make territorial contraction a viable strategy over months or years. Additionally, the ability to occupy any region depended on more than simply the ability to capture sufficient food year round. To maintain a population over the long-term any group would need to be able to occasionally meet adjacent groups, to exchange marriage partners and information, and so the viability of neighbouring groups was also a potential limiting factor. Some inland areas contained enough geographical diversity to allow groups to continue their occupation through the more desertic conditions of the LGM. Lawn Hill River, for instance, was one of several large aquifer-fed rivers running through gorges in the region and providing a chain of reliable resource-rich locations that would have enabled people to move to and from surviving neighbours. Another well-provided location was the MacDonald Ranges of central Australia where foragers could move between springs, gorges and major seasonal rivers to exploit resources and facilitate genetic and cultural contacts.[599]
Across Australia territorial contraction and abandonment, population reductions, reconfiguration of territory and altered inter-group interactions would have been accompanied by transformations of social practices and even of human biology. The biological evidence for adaptation to the ice-age conditions comes principally from southeast Australia, specifically from areas along the Murray River, where skeletons have been excavated at sites such as Kow Swamp and dated to between 22,000 to 9,000 years ago.[600] These skeletons present an image of people who have evolved in response to the ice-age cold, through natural selection that favoured larger, more robust builds.
In the cold conditions during and immediately after the LGM human bodies in southern Australia were 10-20 per cent bigger than more recent Aboriginal people. Skeletons from this period have skulls that are larger, with thicker bones and broader teeth than their descendants, an expected pattern because increased body size and skeletal robustness in cold environments is often observed in animals.[601] The greater body size was more evident in males, leading to a more pronounced difference in size and robustness between the sexes. Such biological adaptations were exaggerated by cultural modifications of the body. For instance, some groups, such as the people at Kow Swamp, marked their identity through artificial cranial deformation of the still-plastic skulls of young children, giving adults exotic long heads with sloping foreheads that would have been instantly recognizable to any observer. Signalling a distinct identity in this way may have reflected local ideologies that had emerged during the LGM as inter-group contact reduced and social characteristics diversified, and/or it may have been designed to provide a benefit in inter-group negotiations. Certainly the practice of artificial cranial deformation was not practised in Australia in more recent millennia; it was a cultural convention that probably emerged during the LGM and subsequently gave way to other forms of social signalling.