The view from Indonesia’s Rote Island towards Australia. Kasih Norman, Author provided
The First Australians were among the world’s earliest great ocean explorers, undertaking a remarkable 2,000km maritime migration through Indonesia which led to the discovery of Australia at least 65,000 years ago.
But the voyaging routes taken through Indonesia’s islands, and the location of first landfall in Australia, remain a much debated mystery to archaeologists.
Our research, published earlier this year in Quaternary Science Reviews, highlights the most likely route by mapping islands in the region over time through changing sea levels.
First landfall on Australia has been argued to be both more difficult and less likely than first landfall at New Guinea, as the final crossing distance from Timor to the continental shelf was more than 80km. It was also thought that the Australian landmass was not visible from any Indonesian island.
Despite this, it was proposed that now submerged islands off the Australian continental shelf were visible from Timor. But until recently, computer technology and ocean floor data sets were not developed enough to know for sure.
A drowned continent
When people first migrated to Indonesia, reaching Australia by 65,000 years ago, they found a landscape that looked very different from today. During an ice age known as Marine Isotope Stage 4, which stretched from roughly 71,000 to 59,000 years ago, western Indonesia formed part of the Pleistocene continent of Sunda, while Australia and New Guinea were joined to form Sahul.
The grey area shows the extent of the ice age continents of Sunda and Sahul, much of which is now under water. The view from Indonesia’s Rote Islandr provided
The rise in global ocean levels at the end of the last ice age at around 18,000 years ago flooded continental shelves across the world, reshaping landmasses. This event drowned the ancient continent of Sunda, creating many of Indonesia’s islands, and split the continent of Sahul into Australia and New Guinea.
This means that what is now under the ocean is very important to understanding where the First Australians might have made landfall.
On the horizon
Our new research uses computer analyses of visibility between islands and continents. We included landscape surface height data of regions of the ocean floor that were above sea level – and dry land – during the last ice age.
The powerful computer programs we used work out what a person standing at a particular location can see in a 360 degree arc around them, all the way to their horizon.
Running more than 10,000 analyses allowed us to pinpoint where people could see to, from any location on any island or landmass in the whole of Island South East Asia.
But because we knew that so many Indonesian islands, and so much of Sahul, were drowned at the end of the last ice age, we also included ocean floor (bathymetric) data in our analyses.
We discovered that in the deep past (between 70,000 to 60,000 years ago, and potentially for much longer), people could see from the Indonesian islands of Timor and Rote to a now drowned island chain in the Timor Sea.
From this island chain it was possible to sight the Australian continental shelf, which in the last ice age formed a massive fan of islands extending towards Indonesia. Much of this landscape is now more than 100m below the surface of the Timor Sea.
Regions with visibility between islands and continents during the last ice age are shown by the connective white lines. Dark grey regions represent the now submerged ice age continent of Sahul, light grey shows landmasses above modern sea level. Kasih Norman
As the island chain sat at the midpoint between southern Indonesia and Australia, it could have acted as a stepping-stone for Australia’s first maritime explorers.
Including the areas of the ocean floor that were dry land in the last ice age means we were able to show that people could see from one island to the next, allowing them to island-hop between visually identifiable landmasses all the way to northern Australia.
These new findings potentially solve another mystery: all of the oldest archaeological sites for Sahul are found in northwest Australia. If people island-hopped from Timor and Rote they would have arrived on the now submerged coastline close to all of Australia’s most ancient occupation sites, such as Madjedbebe[GR2] , Nauwalabila and Boodie Cave.[GR3]
But while we might be closer to understanding where people first reached Australia, signs of the earliest explorers to reach Indonesia have been more elusive.
A team of researchers from the Australian Research Council’s new Centre of Excellence for Australian Biodiversity and Heritage (CABAH) and their partner institution, Indonesia’s National Centre for Archaeology, have now begun the search on Rote and West Timor for the earliest evidence of the region’s first human maritime explorers, the likely ancestors of the First Australians.
[GR1]‘Out of Africa’ stated that the first humans to colonise Australia came from a recent migration of Homo sapiens through South-east Asia. These people belonged to a single genetic lineage and were the descendants of a population that originated in Africa. The fossil evidence for the earliest Indigenous Australians does show a range of physical variation that would be expected in a single, geographically widespread population.
[GR2]The time of arrival of people in Australia is an unresolved question. It is relevant to debates about when modern humans first dispersed out of Africa and when their descendants incorporated genetic material from Neanderthals, Denisovans and possibly other hominins. Humans have also been implicated in the extinction of Australia’s megafauna. Here we report the results of new excavations conducted at Madjedbebe, a rock shelter in northern Australia. Artefacts in primary depositional context are concentrated in three dense bands, with the stratigraphic integrity of the deposit demonstrated by artefact refits and by optical dating and other analyses of the sediments. Human occupation began around 65,000 years ago, with a distinctive stone tool assemblage including grinding stones, ground ochres, reflective additives and ground-edge hatchet heads. This evidence sets a new minimum age for the arrival of humans in Australia, the dispersal of modern humans out of Africa, and the subsequent interactions of modern humans with Neanderthals and Denisovans.
[GR3]Archaeological deposits from Boodie Cave on Barrow Island, northwest Australia, reveal some of the oldest evidence for Aboriginal occupation of Australia, as well as illustrating the early use of marine resources by modern peoples outside of Africa. Barrow Island is a large (202 km2) limestone continental island located on the North-West Shelf of Australia, optimally located to sample past use of both the Pleistocene coastline and extensive arid coastal plains. An interdisciplinary team forming the Barrow Island Archaeology Project (BIAP) has addressed questions focusing on the antiquity of occupation of coastal deserts by hunter-gatherers; the use and distribution of marine resources from the coast to the interior; and the productivity of the marine zone with changing sea levels. Boodie Cave is the largest of 20 stratified deposits identified on Barrow Island with 20 m3 of cultural deposits excavated between 2013 and 2015. In this first major synthesis we focus on the dating and sedimentology of Boodie Cave to establish the framework for ongoing analysis of cultural materials. We present new data on these cultural assemblages – including charcoal, faunal remains and lithics – integrated with micromorphology, sedimentary history and dating by four independent laboratories. First occupation occurs between 51.1 and 46.2 ka, overlapping with the earliest dates for occupation of Australia. Marine resources are incorporated into dietary assemblages by 42.5 ka and continue to be transported to the cave through all periods of occupation, despite fluctuating sea levels and dramatic extensions of the coastal plain. The changing quantities of marine fauna through time reflect the varying distance of the cave from the contemporaneous shoreline. The dietary breadth of both arid zone terrestrial fauna and marine species increases after the Last Glacial Maximum and significantly so by the mid-Holocene. The cave is abandoned by 6.8 ka when the island becomes increasingly distant from the mainland coast.