To my mind, it is a very good piece of public science reporting. I also like the way the authors have included so many links to previous work. My comments should be read as those of a reasonably well informed amateur interested in the implications for his own area of study,
In addition to the piece in The Conversation, there are a number of news reports that contain supplementary information. These include:
- Sci News, New Evidence Pushes Back Aboriginal Occupation of Australia to 65,000 Years Ago
- University of Washington News, Artifacts suggest humans arrived in Australia earlier than thought
- Cosmos Magazine, First Australians arrived 65,000 years ago, archaeological dig suggests
- Science, A find in Australia hints at very early human exit from Africa
- UQ News, Kakadu find confirms earliest Australian occupation
- ABC Science, How do we know how old the Indigenous Madjedbebe rock shelter is?
- ABC Science, Indigenous rock shelter in Top End pushes Australia's human history back to 65,000 years
- Inside Story Digging deeper into a 65,000 year story
"The question of when people first arrived in Australia has been the subject of lively debate among archaeologists, and one with important consequences for the global story of human evolution. Australia is the end point of early modern human migration out of Africa, and sets the minimum age for the global dispersal of humans.
This event was remarkable on many fronts, as it represented the largest maritime migration yet undertaken, the settlement of the driest continent on Earth, and required adaptation to vastly different flora and fauna.
Although it is well known that anatomically modern humans were in Africa before 200,000 years ago and China around 80,000 years ago, many archaeologists believe that Australia was not occupied until 47,000 years ago.
But our research, published today in Nature, pushes back the timing of this event to at least 65,000 years ago.
Map from Science). A small excavation in 1989 at this site had proposed evidence for human activity in Australia at 60,000-50,000 years ago.
But some archaeologists have been reluctant to accept this age. Some pointed to the sandy deposit at the site and argued that the artefacts may have been easily moved down into older layers by trampling or burrowing animals.
Others said the measured ages for the archaeological sediments were not precise enough to support a date of 50,000 years, rather than 45,000 years ago.
Since those excavations in the 1980s, the debate has intensified. Analysis of DNA from the hair of an Aboriginal man who lived 100 years ago suggests that Aboriginal Australians separated from early Asian populations some times between 62,000 and 75,000 years ago.
On the other hand, climate records have implicated humans in megafaunal population collapse at 45,000 to 43,100 years ago, a time frame that had been presumed to correlate with humans’ arrival in Australia."
Dating issues are discussed later in The Conversation piece. The date of 65,000 years is actually plus or minus 5,000 years, so I would be cautious in automatically attaching a higher figure than 65,000 year; 60,000 is the safest number, but may well get older.
Even at 60,000 years, it is still a remarkable number. I have been using 50,000 years as the approximate benchmark for human settlement of Sahul, but will now have to take 65,000 as my working number based on 60,000 plus time to get to the site and colonise the area.
I was unaware of the Chinese discoveries. At this point, and based only on the Nature report, some care needs to be exercised in interpreting these results. In another earlier date, palaeoanthropologist Michael Westaway of Griffith University is quoted referring to archaeological evidence that humans may have been in the Near East 110,000 years ago.
It seems clear based on the flood of recent results is that the spread of homo sapiens was wider and earlier than previously realised, as was the overlapping between modern humans and other hominid species. .
One thing that concerns me, and I lack the specialist expertise to know whether my concern is valid, is what appears to be a growing discrepancy between dating results based on DNA models and those from other dating methods. If the Aborigines were well established in Sahul by 65,000 years ago, then it seems reasonable to assume that they left Africa earlier than the 72,000 date suggested by some DNA analysis.
Within Australia, the latest dates appear to widen the time period during which Sahul was settled, widening the gap between this date and southern dates. I have argued that quick expansion was possible, but a longer time period does seem reasonable. However, the results do raise questions in my mind about the exact pattern of settlement of Sahul.
If I remember correctly, the earlier DNA studies showed a north west gradient from Cape York to South West Australia. This was interpreted as supporting coastal migration in both west and east from the original group or groups. In the east, my view has been that migration could well have come along the slopes of the Great Dividing Range instead of or as well as the coast. I also read the material as suggesting that that the Papuans and Aborigines came from a single stock that then diverged. This could be accommodated via settlement on Sahul in either what is now PNG or Australia and then spread or separate migrations from a common stock to different points.
The latest results have raised all sorts of questions in my mind:
- How widespread in what is now South East Asia were were the Aboriginal precursors? Was it just small groups, that has been an implicit assumption, or did they occupy significant territory?
- What happened to the Aborigines who remained behind? Were they supplanted by later arrivals?
- Did something trigger migration or was it just search for the new, natural migration?
- Were there several migration to different or the same spots separated in time?
One thing that does stand out from the results is the apparent sophistication of the early tool kit and the life implied by that. These people were already in control of their environment, living an apparently sophisticated hunter/gatherer life style. I think that's very important. It's a reasonably assumption that their precursors were more advanced as well than has sometimes been assumed. I think that this requires a change in our thinking in terms of both the options open to them and their capacity to meet new challenges.
To make new research possible, a landmark agreement was reached between the University of Queensland (and associated researchers) and the Gundjeihmi Aboriginal Corporation representing the Mirarr traditional owners of the site.
The agreement gave ultimate control over the excavation to the Mirarr senior custodians, with oversight of the excavation and curation of the material. The Mirarr were interested to support new research into the age of the site and to know more about the early evidence of technologies thought to be present there.
New digs, new dates
In 2012 and 2015 our team excavated an area of 20 square metres at Madjedbebe. We found artefacts in three distinct layers of occupation.
Among the artefacts in the lowest levels we found many pieces used for seed grinding and ochre “crayons” that were used to make pigments. Our large excavation area allowed us to pick up very rare items, such as the world’s oldest known edge-ground hatchets and world’s oldest known use of reflective pigment.
During the excavations we recorded the three-dimensional coordinates of more than 10,000 stone artefacts using a laser total station. This device sits on a tripod and uses a laser and prism to record the location of artefacts and other features at millimetre accuracy, thus giving a very precise record of artefact position and layering.
We analysed these coordinates to test previous criticisms that artefacts may have moved a lot in the sand. We found some broken artefacts that we could fit back together, and by measuring the distance between these pieces we can understand how far artefacts have moved.
We also conducted an experiment to observe the movement of artefacts on the ground when people walked over them. These results allow us to respond to the earlier critics with data that point to a relatively small amount of movement, not enough to mix artefacts between the three distinct layers of occupation that we found in our excavations.
During the excavation we collected many kinds of samples for specialised analyses, including more than 100 samples for dating. We used both radiocarbon dating and Optically Stimulated Luminescence (OSL) methods to find the ages of the artefacts. Because radiocarbon dating is limited to samples younger than 50,000 years ago, we relied on OSL to help us find the ages of the lower part of the site.
OSL methods estimate the time elapsed since sand grains were last exposed to sunlight. Australian archaeologists have been wary of OSL methods because often in the past OSL involved sand grains measured together in a little group, resulting in ages that were not very accurate.
To get more precise ages, we measured thousands of sand grains individually, rather than in a group. We also had another lab analyse some samples to make sure our results were reliable. The result is that we have a convincing age for the settlement of Madjedbebe, and Australia, of 65,000 years ago.
I think that this section illustrates the remarkable changes that have taken place in the multidisciplinary science that archaeology has become. The use of laser scanning popularised by the TV Programme Time Scanners allows accurate measurement of the placement of objects; the team used ground penetrating radar to survey the area before digging a-la Time Team; while the use of OSL dating requires high technology science.
It is not possible for the non-specialist in these technical areas to make sensible judgments on detail beyond noting that the scientific method applied seems quite rigorous. It is possible for the non-technical observer to make judgments about the extent to which results seem to diverge from other evidence. In this context, the results while interesting and important do not seem to conflict with what we already know. In that sense, they pass the academic pub test!
These new dates throw light on a few puzzles in the overall picture of human evolution.
Our ages suggest that modern humans and Homo floresiensis in eastern Indonesia may have co-existed for 15,000 years. This means that the arrival of modern humans did not necessarily cause other ancient human-like species to become extinct.
If it’s the case that people have lived in Australia since 65,000 years ago, it may also be true that humans and megafauna co-existed for 20,000 years before megafauna went extinct across the continent.
Until now we knew very little about the technology and lifestyles of the first Aboriginal people. The oldest artefacts from Madjedbebe help to tell this story. They indicate that the earliest Aboriginal inhabitants of Australia were innovative people who – like humans everywhere on earth – developed solutions to new problems and engaged in symbolic and artistic expression.
We found evidence for the mixing of ochre with reflective powders made from ground mica to make a vibrant paint. Currently the oldest known rock art in the world is dated to 40,000 years ago in Sulawesi (a possible stepping stone to Australia). But the abundant ground ochre and use of mica indicates that artistic expression took place in the region much earlier.
We also found new forms of stone tools such as edge ground hatchet heads (and even the grinding stones used to sharpen them), useful in cutting bark and wood, shaping wooden tools and extracting difficult to obtain foods from trees.
The grinding stones from the site indicate a range of fruits, seeds, animals and other plants were ground up for food. These are the oldest known examples of seed grinding stones found in Australia, if not the world.
In ancient fireplaces from the site we also recovered pieces of burnt pandanus nuts, fruit seeds and yams, which give us clues as to the earliest plant foods consumed at the site. Some of these foods continue to be eaten today by Mirarr and other Aboriginal people in the Top End.
Our new ages suggest that Australia was settled well before modern humans entered Europe about 45,000 years ago. This means that the earliest art and symbolism in Europe is of limited relevance to understanding modern technology and symbolic expression in South and Southeast Asia and Oceania.
Our results help to show the unique place of the Eastern hemisphere, and Australia in particular, in understanding how and where modern humans appeared.
Some of this material is very Australian-centric. The comparison with Europe and indeed the age of art is really neither here nor there. I would have thought it self evident that the earliest art and symbolism in Europe is of limited relevance to understanding modern technology and symbolic expression in South and Southeast Asia and Oceania, although comparisons from elsewhere can always provide clues and questions.
The Eastern hemisphere, and Australia in particular, may or may not have a unique place in understanding how and where modern humans appeared. I would have thought that that place was still occupied by Africa. What is important is the extent to which the discovery does two things:
- provide further evidence on the dispersal of modern humans and their overlap with other hominids
- further illuminate the history of Aboriginal Australia.
This is where I have a degree of frustration with the reporting. So much is focused on the early date and the sophistication shown in the material remains. These are important, but what have we learned after arrival, how does this fit in with Aboriginal history after arrival?
We learn that there were thee intense occupation phases, with some differences between. We learn that the climate was cooler and wetter when the Aborigines came. We learn that there was little apparent difference in the vegetation over the millennia since first settlement; that surprised me. But it still doesn't really help us in writing a history of Aboriginal Australia where the real focus has to be the period after first arrival. Mind you, the material may be there, not just reported! Meantime, back to my more local focus.