It emerges that people reached Australia earlier than was thought. This finding casts light on the technology used by the travellers, and their possible interactions with animal species that became extinct. See Article p.306
When did ancient humans, dispersed from Africa, reach some of the most distant corners of the world? And which technologies were associated with these early travellers? On page 306, Clarkson et al.1 report an analysis of archaeological fieldwork in Australia, and propose a revised timeline for the peopling of this continent.
Around 70,000 years ago2, a group of African people moved into Asia, probably through the Sinai peninsula in Egypt and into the Negev Desert, as part of a journey that was the most consequential dispersal event of our species in the history of our planet. The descendants of these early travellers pushed into Europe, eastern Asia, Australia and the Americas, and eventually reached the remaining unpopulated islands such as Madagascar and New Zealand. This diaspora resulted in altered environments, was associated with the eventual disappearance of related species from the family tree of humans, such as the Neanderthals, and set the stage for the formation of the main human genetic lineages that have given rise to different ethnic and linguistic groups. Moreover, the dispersal also overlapped in time with the extinction of many animal species.
Hunter-gatherers, using nothing more than Stone Age technology, accomplished all but the final leaps in the most far-flung global explorations, and in one particularly spectacular journey, they must have built ocean-worthy vessels and sailed to Australia. The timing of that jump to the 'land down under' has been an ongoing focus of debate, with some researchers concluding that it occurred no earlier than around 45,000 years ago3.
Palaeoanthropologists have thought that, by 45,000 years ago, humans had dispersed to opposite sides of the world, reaching both Europe and Australia. But anyone familiar with the main methods of archaeological dating that are used to reach such conclusions might be sceptical, given that the maximum age for which radiocarbon dating can provide accurate and precise results is for dates around 40,000 to 45,000 years ago. Pointing confidently to a maximum age of 45,000 years, when relying on radiocarbon dating alone, could therefore be a form of confirmation bias.
Fortunately, geochronologists have been hard at work, driven by the possibility of developing techniques to answer questions that are beyond the reach of radiocarbon approaches. One of the most productive such techniques is known as optically stimulated luminescence (OSL), which is applied to mineral grains such as quartz. OSL can establish the age of sediments by determining when light last irradiated a mineral grain4, and provides a way of estimating how long a sample has been buried (Fig. 1). When the conditions are right, OSL-based analysis can give reliable information on more-ancient time frames than is possible by radiocarbon dating.
Armed with OSL technology, Clarkson and colleagues visited Madjedbebe, one of the most debated archaeological sites in Australia. Formerly known as Malakunanja II, it had been excavated on two previous occasions5,6. Clarkson and colleagues re-excavated the site (Fig. 2) using high-resolution field techniques and survey instruments called total stations that allow the direct, accurate measurement of the 3D location of found artefacts. This enabled the team to record the locations of its observations with exceptional precision.
The authors sampled organic material and sediment grains for use in radiocarbon and OSL dating down through the excavated layers, enabling them to compare the results from both techniques and to directly overlap this information about age with the plotted artefacts such as stone tools. Within the time frame for which accurate radiocarbon dating is possible, both sets of results are consistent with each other. However, when the limit for radiocarbon dating was reached, OSL was used to date the older layers, allowing the researchers to determine a date for the earliest human occupation of the site. They then used a Bayesian statistical technique to develop an age model for the site that reduced the impact of the potential imprecision of individual dates and provided estimates of age for undated layers between those they had dated. In this way, Clarkson and colleagues show that human occupation of Australia occurred well before 50,000 years ago (and most probably before 65,000 years ago), and that these early Australians had a full complement of advanced Stone Age technology, as demonstrated by the artefacts found at the site.
The outcomes of scientific debates on the extinctions of large animals (megafauna) remain highly contentious, particularly in relation to Australia. A few years ago, I attended a conference at which there was a fierce discussion about whether humans were the agents of extinction of various Australian megafauna. The fantasy still exists that hunter-gatherers lived in harmony with nature, and in some circles it is thought to be the job of anthropologists and archaeologists to protect this empirically incorrect idea. What evidence do these researchers rely on to support this idea? Normally, it is the absence of an association between extinct animals and humans, as well as the lack of evidence for human occupation at times early enough to be consistent with humans causing the extinctions.
Yet for reasons of basic probability, it is unlikely that we will ever find the 'first' settlers of a land, or even direct evidence for the hunting of extinct megafauna7. So our estimates of the 'earliest' occupation might underestimate its actual timing. A paper8 published in 2016 showed that early Australians had penetrated the harsh arid interior of Australia by around 49,000 years ago, and those researchers found the earliest definitive evidence for megafaunal fossils in association with tool-like artefacts in Australia. Taking this work together with the findings of Clarkson and colleagues now provides compelling evidence that humans were in Australia early enough to cause many of the megafaunal extinctions.
My PhD adviser, J. Desmond Clark, who studied African archaeology, regularly exhorted his students to get out of the office and “go put holes in the ground”. Fieldwork is hard and challenges one's life in myriad ways. Yet we need not only discover sites, but also return to the old ones with new methods with which to refine what we know. The latest work in Australia shows us the pay-off, and provides a reminder that this massive continent could reveal many other secrets during future fieldwork. Such studies might also further increase our understanding of the pace and character of human colonization, and its impact on the fauna and flora of that time.
We now know that modern humans, after they left Africa around 70,000 years ago, dispersed rapidly to a coastal area that became the departure gate for their journey to Australia. From that launch pad, perhaps some of them envisaged other lands across the water that they could not see. They decided to take a chance and built boats, loading them with both new and tested technologies. Then, with their families, they boarded to embark on a journey of discovery. Sounds familiar — sounds like humans reaching for the stars.Footnote 1
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About this article
Proceedings of the National Academy of Sciences (2018)
Breaking through the radiocarbon barrier: Madjedbebe and the new chronology for Aboriginal occupation of Australia
Australian Archaeology (2017)