Climatic Deterioration After Aboriginal Colonisation of Australia

Australia: The Land Where Time Began

Climatic Deterioration After Aboriginal Colonisation of Australia

According to Hiscock though the early Aboriginal settlers are indicated by genetic and archaeological evidence to have been highly adaptable, spreading rapidly across different environments, it does not mean they were able to adapt to every environment. For the initial stage of settlement minimal evidence has been found that would suggest the colonists were settling in sandy deserts, which reveals that the people settled in many, but not all, niches. The evidence that has been found indicates that during the Pleistocene foragers were least able to occupy environments that were poor in resources, and this conclusion has been reinforced by the profound difficulties that were encountered by humans as the climate deteriorated.

Beginning about 45,000 BP the climate was trending towards cool, dry conditions, but about 30,000 BP the last glacial cycle intensified rapidly, with the onset of a cold, dry period, the OIS2 (Oxygen Isotope Stage 2). Sea levels dropped dramatically at this time to reveal the continental shelf to a depth of almost 150 m below the sea level the present, as moisture was locked up in ice or snow at high latitudes (Lambeck et al., 2002). The area of the landmass that was available for settlement by humans was greatly increased by the extensive exposure of the continental shelf and the environments in which they had already settled were changed. With many inland areas then even further from the sea than they had been (Chappell, 1991; Lambeck & Chappell, 2001; Yokoyama et al., 2001; Lambeck et al., 2002). After 30,000 BP the increasing dry, continental situation of inland areas compounded the effects of drying climates.

According to Hiscock the deterioration of the climate can also be described as increased evaporation and/or reduced precipitation in many regions. Monsoonal rain was reduced greatly about 30,000 BP; Lake Eyre dried out, a condition which didn’t change until around 10,000 BP (Miller et al., 1997; Magee & Miller, 1998; B.J. Johnson et al., 1999). At this time Lake Mungo and nearby lakes were lower and water levels fluctuated and dune-building processes were activated (Bowler, 1983, 1986, 1998). There were also reduced water levels at other lake systems during this period, though the timing of drying varied locally (Harrison, 1993). In many regions the reduced effective precipitation led to decreasing trees/shrubs in many regions, as well as an increased expansion of grasslands (see review in Hiscock & Wallis, 2005.

Throughout the continent average air temperature dropped, which affected vegetation that was sensitive to temperature, and the snow lines were lowered compared to those of the present. Summer temperatures were 6-10⁰C cooler than at present in montane portions of Tasmania (Barrows et al., 2001). Chemical analysis of the proteins in emu eggshell from central Australia which preserve a record of temperature demonstrate that between 30,000 BP and 20,000 BP it was at least 6^oC cooler than at present (Miller et al., 1997; B.J. Johnson et al., 1999).

Desert landscapes were enlarged by changes in precipitation, temperature and availability of surface water acting together. At this time the semi-arid zone expanded laterally towards the margins of the continent, as the areas that had been semi-arid became arid (Jones & Bowler, 1980). The deserts that had been present during earlier wetter, warmer phases became more inhospitable than they are at present. Many large lacustrine systems that had previously been reliable disappeared, as inland environments became drier. Initially the settlers may have been helped to adapt to the new, drier conditions as the climate was also becoming less variable.

Many groups continued occupying inland regions early in OIS2, possibly refining their economic strategies to suit the landscapes that were evolving around them. The familiarity of the people with their environments is reflected in the localised adaptations to landscapes of the interior, which has resulted in different patterns of activity being recorded for each region. An example of this is the finding that increased amounts of cultural material were present in some areas, but other areas produced decreased amounts of cultural material (Veth, 1989; O’Connor et al., 1998; O’Connor et al., 1999; Hughes & Hiscock, 2005). Social networks and regular use of resources characterise this period. Large quantities of food debris found at several inland lakes indicate that edible resources were being exploited by large groups of people (Balme, 1983, 1995). The procurement of ochre from distant sources by the occupants of Puritjarra continued, as they had for 10,000 years (M.A. Smith et al., 1998). This has been interpreted (Hiscock & Wallis, 2005) as evidence for initial economic strategies, that were partly dependent on reliable access to surface water, as well as being focused on riverine and lacustrine resources that were supplemented by terrestrial resources that were available nearby, and this continued to be effective for many foragers in the inland during the period from 35,000 BP to 30,000 BP. Archaeological evidence of human occupation has been found from the start of OIS2 in deserts that have resources, and contain uplands, major co-ordinated drainage and/or extant lake systems; whereas there was little or no occupation in many regions that lacked those resources. It is indicated by current archaeological evidence that sandy deserts without coordinated drainage and large permanent lakes were difficult environments for human habitation during OIS2, as was predicted (Veth, 1989). Following the further deterioration of the climate that occurred by the end of OIS2, there was a strong and widespread avoidance of dry, sandy environments (Hiscock & Wallis, 2005).

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