by Patrick Nunn
Within the last 34 million years in Australia, the work of denudation – or land-surface lowering – has been assisted by the continent’s inexorable move into increasingly warmer climate zones. At the start of this period, recently separated from the continent of Antarctica (part of the ancient Gondwana continent), Australia was located in the very cold and dry high latitudes of the southern hemisphere. Since then it has steadily moved north into lower latitudes.4 While punctuated by wetter episodes, which were comparatively short-lived, the aridity that currently dominates Australia’s climate started to affect the continent about 10 million years ago, when it reached the horse latitudes: those zones of the Earth where the high-pressure atmospheric conditions result – for most of the time – in warm weather, weak winds, few clouds and above all little rainfall.
You might therefore expect that the surface of the Australian continent has been little altered from the time it first formed – but of course this is not the case. Time is the great leveller, for the Earth-forming processes of weathering and erosion, however slow they may be, are relentless. Across almost countless eons, driven by changing temperatures, wind and rain, and running water, the land surface of Australia has been worn down. A lack of processes such as volcanic eruptions and land uplift, which elsewhere in the world rejuvenate ancient land surfaces and cause lost nutrients to be replaced, has led to a situation in Australia where soils have been weathered and leached repeatedly.
Being dry, low and somewhat slothful as moving continents go does not sound like a great recommendation for the study of Australian geology, but the reality is quite different. Australia is composed mostly of continental (not oceanic) crust, and is home to some of the earliest-known rocks on Earth, formed almost 4.5 billion years ago, outcropping in the Jack Hills of Western Australia.5 In the same region, the remains of some of the very first life forms to appear on our planet are found. Known as stromatolites, they lived in colonies and built structures using carbonate extracted from seawater. There are living stromatolites in Shark Bay, yet a few hundred kilometres away they are found as fossils in rocks that formed 3.5 billion years ago, intriguingly close to the time Planet Earth came into being.6
Beneath the blanket of weathered sediment that covers most of the Australian landscape lies a complex pattern of bedrock testifying to the billions of years the continent has existed.7 Some of this bedrock represents the cores of ancient continental masses (cratons), while other bedrock consists of remains of the sediment-choked basins that accumulated around them. About two-thirds of Australia’s basement formed more than 500 million years ago.
Big land masses provide more opportunities than smaller ones for terrestrial life. Newly arrived organisms can spread out in many directions, possibly multiplying uninhibitedly at first, utilising the food sources they encounter. Food species might renew themselves indefinitely while predator population densities often remain low, below an area’s carrying capacity. Such a scenario is thought to explain why the first Australians – ancestors of today’s Aboriginal peoples – were able to successfully follow a largely nomadic way of life for more than 50,000 years; no other was needed to survive. Yet the climate of Australia also localised the possibilities for life that might otherwise be expected from its great size. Rainfall is concentrated along the continent’s fringes, leaving a vast arid interior that poses many challenges for living things – including humans. Winds that blow onto Australian shores, often laden with moisture from their cross-ocean travels, drop most of it within a few hundred kilometres of the coast, then continue blowing inland. They are dry and pick up dust as they howl across the great inland plains to the furthest inland places where, finally, the wind losing power, the dust drops to the ground, driven into dunes in the sandy deserts.8 Some of the deserts are stony – this is where renewed winds have removed the finer particles, leaving behind those it cannot readily shift.9
Compared with continents of similar size, there are not many large rivers in Australia, especially in its western half. In the centre, dry riverbeds connect series of dry lake basins that only rarely become filled with water. On such occasions, usually when a La Niña event is in progress, the desert turns green, its livelihood possibilities burgeon and its living inhabitants rejoice. When some of these lakes are brimful with water, their surfaces may become very flat and they may become almost indistinguishable from the sky when the sun is high: a phenomenon that may have given rise to legends about a vast inland sea. On his last expedition, so convinced was Charles Sturt that he would find the inland sea, he took a boat along so that he would be able to paddle across it once he found it. On 13 May 1845, an elderly Aboriginal person stayed in Sturt’s camp and was ‘greatly attracted by the Boat … the use of which he evidently understands’. Mesmerised, Sturt reported that this man ‘pointed directly to the northwest as the point in which there was water, making motions as if swimming and explaining the roll of waves, and that the water was deep’.10 Sturt’s informant is likely to have been describing the Indian Ocean, although maybe memories of times when the dry lakes periodically filled clouded his thoughts. There has never been a sea in the centre of Australia.
The earliest known traces of human settlement in Australia date from some 40,000–60,000 years ago and are not found along the modern coast. They are found inland, typically beneath rock overhangs or in shallow caves where people once sheltered, commonly hundreds of kilometres up river valleys from the modern coastline. So of course these places cannot be the first that people settled in Australia. They must have set foot on the land hundreds, perhaps even thousands, of years earlier than the time they reached these inland shelters, but those first footprints are forever lost to us today. This is not simply because no earlier indications of a human presence in Australia have been found along its coasts, but also because at the time people arrived here first, the sea surface was much lower than it is today. The shore on which the first people landed is now under tens of metres of ocean water, probably buried by sediments washed off the land, and perhaps even grown over with reef.
So can we know where and when the first Australians actually became Australian, or when the first human footprint appeared on Australian shores? We can use various methods to get approximate answers to these questions, including the reconstruction of the easiest series of sea crossings from Asia, or genetic tracing or even historical linguistics, which tell us where in Australia the majority of extant Aboriginal languages originated. All this is discussed later, but it is sensible to begin our quest for the first Australians by looking at the places where they first manifested themselves.
Determining ages for the earliest human settlement sites in Australia suffered for a long time from being beyond the reach of radiocarbon dating – approximately 40,000 years – but within the past 25 years newly developed techniques have been applied to diagnostic material from ancient sites that allow their ages to be accurately determined. Several such early sites are discussed below; their locations are shown in Figure 2.2.
In northernmost Australia are found a number of ancient sites, notably the two rock-shelter sites of Malakunanja,11 and Nauwalabila (in the somewhat alarmingly named Deaf Adder Gorge). Dates for the deposition of sand containing the oldest human-made stone tools (artefacts) at Nauwalabila range from 53,000 to 60,000 years ago,12 while those at Malakunanja are sandwiched between sediment layers dated to 45,000 and 61,000 years ago respectively.13
The earliest Australians used tools they made from stone, and perhaps shell, which they would have discarded when they ceased to be functional (or cherished) – like we often throw away things we no longer need or want today. Stone tools often endure the ravages of millennia, and should we find them today, we can often work out how long ago they were used – and thus approximate the time when their users occupied a particular place. So much of the calibration of ancient tool-using human history in Australia and elsewhere has come from working out the chronologies of tool evolution.14
Figure 2.2 Locations of
some of the earliest known human settlement sites in Australia and New Guinea first occupied at least 40,000 years ago. The lighter-grey shaded area was dry land at the time people first arrived in Australasia from island South-east Asia about 65,000 years ago, when the sea level was about 70m (230ft) lower than it is today.
The Devil’s Lair site in south-west Australia is within a large limestone cave, 5km (3 miles) from the modern coast. The lower parts of the cave are packed with sediments containing evidence for a human presence, including stone tools, bones and – critically for precise age determination in such ancient contexts – charcoal preserved in ancient hearths. The oldest (deepest buried) of these is found almost 3.8m (12ft) below the surface of the cave floor and has been dated to about 45,470 years ago. However, there are other indications of a human presence in layers below this hearth, suggesting that the first human occupation of this cave was at least a few thousand years earlier.15
Limestone caves are also sites of early occupation within the catchment of the Fitzroy River in north-west Australia. The Mimbi Caves include a cave named Riwi in which at a depth of just 65–70cm (25–28in) were found two hearths dated to more than 40,000 years ago. At the Carpenter’s Gap rock shelter, 200km (125 miles) away, the sediment fill is full of well-preserved charcoal, showing that human occupation occurred here about the same time.
Finally, on mainland Australia there is the remarkable discovery of a human skeleton on 26 February 1974 in a sandbank on the shore of Lake Mungo (part of the dry Willandra Lakes system). The body had been laid in a shallow grave, then sprinkled with powdery red ochre before being buried. The first studies to date the bones used various methods and suggested that this man – Mungo Man – died sometime between 61,000 and 62,000 years ago.16 More recent research shows conclusively that this was an overestimate. The earliest unequivocal signs of a human presence in the Lake Mungo area are from sands in which stone flakes – which could only have been created by people deliberately banging one piece of rock against another – are found; they bracket human arrival in the vicinity at between 45,700 and 50,100 years ago.17
The first Australians used fire, burning wood to form ash and charcoal. Some fires were wide ranging, intended to clear woodland of its undergrowth to flush out animals, expose vegetation and stimulate regrowth to which prey animals would then be attracted. Other fires were for cooking, the ubiquitous hearths or fire pits, the remains of which are often found buried within the sediment fills of caves and rock shelters where some of the first Australians once lived. As is the case with the remains of any carbon-rich life form, the age of charcoal can be determined precisely using radiocarbon dating, giving us insights into exactly when a particular tree was alive: often a reliable proxy for the time when the humans who burnt it occupied a particular place.18
As can be deduced from the occupation ages of inland sites discussed above, it seems likeliest that people occupied most of Australia 40,000–60,000 years ago, but there have been suggestions that their arrival was far earlier. The most common type of supporting evidence is that from concentrations of charcoal within long sediment cores from lake beds or the shallow ocean floor, which point to an unusually high incidence of bush fires at a particular point in time, suggesting (yet not proving) the arrival in a landscape of people who burnt the vegetation in order to access food.19
Such an idea was mooted in 1997 for the Queensland coast following analysis of an offshore core,20 but was more famously proposed earlier when sediments from the floor of Lake George, just outside Canberra, Australia’s capital city, were analysed. Lake George is usually mostly dry these days, but its form shows clearly that it was once a lake. A core 72m (236ft) long drilled into its sediment fill allowed scientists insights into its environmental history going back at least 4.2 million years. For our purposes, the critical layer (Zone F) is packed with charcoal – in stark contrast to most of the rest of the core – and was dated as having formed on the lake floor about 120,000 years ago.21 Huge excitement greeted this discovery as commentators interpreted it as implying the first human occupation of Australia to have been far, far earlier than anyone else had hitherto suggested. Yet this age is an outlier among early proposed ages for human occupation of Australia, and for this reason is today widely regarded as wrong. Had it been correct, it would be expected that confirmatory ages from other sources would have since been forthcoming, which is not the case.22
A similar story of early human occupation comes from what is today Papua New Guinea, which was – because of a lower sea level – contiguous with the Australian mainland for most of the time people have lived there. A key site is the Huon Peninsula in the east of the main island. Due to its long-term uplift, this peninsula appears like a giant staircase, each step representing a coral reef that formed at a particular time. Stone axes with distinctive ‘waists’ for easy handling are found in sediments associated with the reef that formed at least 40,000 years ago, showing that people using this comparatively sophisticated technology were present in the area at this time.23
Thus while there is solid evidence suggesting that people were living in Australia and Papua New Guinea 40,000–60,000 years ago, most of the sites where their presence has been detected lie well inland of the modern coast. This seems a bit odd if you forget that, at this time, the sea level was much lower than it is today, so that the Australian coastline would have been much further out to sea. Australia would have been bigger, connected to the main island of New Guinea and closer than it is today to the islands of South-east Asia, from which we know the first Australians came. Perhaps these first settlers started their journeys on the coasts of Borneo or Java, ‘hopping’ by boat from island to island across the straits to reach the Australasian mainland. For this reason we might expect to find the oldest sites in Australasia somewhere in western New Guinea or northernmost Australia.
This inference seems borne out by the early age – perhaps as much as 65,000 years ago – for the occupations at Malakunanja and Nauwalabila, but even these sites would have been significantly inland at the time of first settlement, so that they were likely to have been occupied long after people first set foot in Australia. Just how long the lag was is of great interest – and worth a bit of conjecture. Given that the first arrivals were probably accustomed to feeding themselves from coastal ecosystems, it is plausible to suppose that settlement of the interior did not become a priority for several generations, perhaps only after coastal population densities increased, thereby increasing pressure on proximal food resources. It seems more likely that we are looking at a few thousand rather than a few hundred years, so if we accept that the earliest dated occupations are close to 60,000 years ago, then a time for initial human arrival of 65,000 years ago appears plausible.24
Many of those who have studied Indigenous Australian cultures argue that for most of the time they have existed in Australia, they remained isolated from the rest of the world’s people. In almost every part of the continent, Aboriginal cultural practices and languages show clear signs of having evolved without the outside interference – the cross-cultural syncretism – that can often be so readily unpicked in cultures elsewhere. The reason for the extraordinary isolation of Australian Aboriginal cultures for so many tens of millennia is likely to lie in geographic isolation – and the fact that ocean gaps proved more formidable barriers to potential migrants than they evidently had for the first arrivals. Such inferences have been confirmed by studies of DNA in skeletal remains.25
In 2012, a discovery was made that shook the foundations of the long-held belief in the cultural isolation of Australia. When the first written accounts of Australia appeared in the late eighteenth and nineteenth centuries, many made mention of a distinctive wild, pointy-eared dog – the dingo – that was used by Aboriginal people as a hunting companion (although latterly it has become the scourge of sheep herds). At the time of European colonisation of Australia in 1788, the dingo was everywhere on mainland Australia except the offshore island of Tasmani
a. This observation proved critical to understanding when the dingo arrived in Australia. It could not have been, as was once assumed, as the ocean-going partner of the first human arrivals, for then it would surely have joined them in Tasmania, crossing the Bass Strait land bridge when the sea level was lower than it is today. The last time the ocean rose across the Bass Strait, cutting off Tasmania and its human inhabitants from the rest of Australia, was about 14,000 years ago.26 We can therefore infer that, give or take a few millennia, the dingo was not present on mainland Australia at this time.
This intriguing scenario, which implies that the dingo must have been a significantly later arrival than the first Australians, is borne out by research into dingo DNA. The diversity of this within modern Australia is consistent with the dingo being introduced sometime between 4,600 and 18,300 years ago.27 Put this conclusion alongside another that argues for an episode (well before European contact) of ‘substantial gene flow’ between Australian Aboriginal people and those of the Indian subcontinent, and it is tempting to imagine a small fleet of people and their companion animals (including dingos) sailing south-east from Tamil Nadu, headed perhaps for Sri Lanka or Indonesia, being swept off course and fetching up on Australian shores. While the dingos multiplied in this new land, the human migrants became absorbed into Indigenous Australian cultures, eventually becoming indistinguishable from the original occupants except for the telltale signs in their DNA.28