Sahul

Sahul refers to the prehistoric continental landmass that once connected Australia, New Guinea, and Tasmania during periods of low sea level in the Pleistocene epoch. This ancient supercontinent formed part of the Australasian region, and it played a crucial role in the early human migration and biogeographical evolution of species in this part of the world. The term distinguishes this continental shelf from Sunda, the Asian counterpart that linked the islands of Southeast Asia to the mainland during the same period.

Geological Background

The formation of Sahul dates back to the Quaternary period, when fluctuations in global climate caused alternating glacial and interglacial cycles. During glacial maxima—particularly around 70,000 to 18,000 years ago—sea levels were 100 to 150 metres lower than today, exposing vast areas of the continental shelf.
This exposure joined mainland Australia, New Guinea, and Tasmania into one continuous landmass. The Arafura Sea, Gulf of Carpentaria, and Torres Strait, which today separate Australia from New Guinea, were then dry land. Similarly, the Bass Strait between Australia and Tasmania formed part of the exposed continental plain.
When the ice sheets melted during the Holocene epoch, rising sea levels submerged these connecting plains, isolating Australia, New Guinea, and Tasmania as separate landmasses roughly 8,000 to 10,000 years ago.

Geological Structure and Extent

The Sahul Shelf covers an area of about 7.6 million square kilometres and includes:

• The Australian continent
• The Arafura Shelf and Gulf of Carpentaria region
• The Papuan Shelf of southern New Guinea
• The Bassian Plain, now beneath the Bass Strait

This continental shelf is part of the Indo-Australian Plate, which is geologically stable in its interior but bordered by active tectonic zones in the north and east, particularly near the New Guinea Highlands and Coral Sea regions.

Human Migration and Settlement

The existence of Sahul was instrumental in facilitating early human migration into the Australasian region. Anthropological and archaeological evidence suggests that the first humans arrived in Sahul around 65,000 years ago, making them among the earliest known seafarers in human history.
These early settlers are believed to have travelled from Sunda, the exposed Southeast Asian continental shelf, across a chain of islands known as Wallacea—a biogeographic region that remained partially submerged even during glacial periods. Although the sea crossings required were modest compared to modern oceans, they still demonstrate remarkable navigational skills for the period.
Once humans reached Sahul, they dispersed across its vast expanse, adapting to diverse environments ranging from tropical rainforests in the north (New Guinea) to arid deserts in the south (Australia) and temperate forests in the southeast (Tasmania).
By about 45,000 years ago, human populations had spread throughout the landmass, leaving archaeological evidence such as tools, rock art, and campsites in regions like Arnhem Land, Kimberley, and Lake Mungo.

Flora and Fauna

The biogeography of Sahul was distinct from that of Asia due to the persistent oceanic barrier known as the Wallace Line, named after naturalist Alfred Russel Wallace. This biogeographical boundary separated the fauna of Asia (Sunda) and Australasia (Sahul), resulting in unique evolutionary pathways.
The Sahul landmass supported a wide range of endemic species, many of which have no counterparts elsewhere:

• Marsupials such as kangaroos, wallabies, wombats, and diprotodonts
• Monotremes such as the platypus and echidna
• Giant megafauna including Diprotodon (a giant wombat-like herbivore), Procoptodon (giant kangaroo), and the predatory Thylacoleo carnifex (marsupial lion)
• Flightless birds such as Genyornis and large reptiles including Megalania, a giant monitor lizard

New Guinea, being tropical, evolved differently, developing dense rainforests that supported marsupials such as tree kangaroos and cassowaries, while Tasmania had temperate forests and glacial landscapes.
The separation of Sahul’s components due to rising sea levels caused speciation and diversification, as isolated populations evolved independently in Australia, New Guinea, and Tasmania.

Cultural Development

The peoples who inhabited Sahul developed diverse cultural traditions adapted to their specific environments. Archaeological findings show early evidence of rock art, stone tool industries, controlled use of fire, and complex social organisation.
After sea levels rose and cut off land connections, the populations in Australia, New Guinea, and Tasmania became isolated:

• In Australia, the descendants became the Aboriginal Australians, whose cultures are among the world’s oldest continuous traditions.
• In New Guinea, societies developed agriculture independently around 10,000 years ago, cultivating crops such as taro and yam in the highlands.
• In Tasmania, isolation for over 10,000 years led to unique adaptations in technology and lifestyle suited to colder climates.

These cultural trajectories demonstrate how environmental changes shaped human diversity within the broader Sahul framework.

Palaeoenvironment and Climate

During the Last Glacial Maximum (around 21,000 years ago), Sahul experienced cooler and drier conditions than today. The interior regions of Australia were arid, with vast desert expanses, while New Guinea maintained tropical rainforest ecosystems. The expanded coastal plains provided migration corridors and resource-rich areas for early human populations.
As deglaciation progressed, rising sea levels flooded the low-lying areas of the Arafura and Torres plains, separating New Guinea from Australia. Similarly, the Bassian Plain was submerged, isolating Tasmania. This transformation drastically altered both human settlement patterns and faunal distribution.

Scientific and Archaeological Significance

Sahul holds exceptional significance in the study of human evolution, biogeography, and climate change. The discovery of early sites such as Madjedbebe (Northern Territory), dated to about 65,000 years ago, provides crucial evidence of the antiquity of human presence in Australia.
Other major archaeological and palaeontological sites include:

• Lake Mungo (New South Wales) – evidence of early burials and cultural activity.
• Kuk Swamp (Papua New Guinea) – early agricultural terraces dated to around 10,000 years ago.
• Devil’s Lair (Western Australia) – one of the oldest continuous occupation sites.

These discoveries collectively illustrate how early humans adapted to environmental changes across the Sahul landmass.

Modern Relevance

Today, the concept of Sahul is central to studies in palaeogeography, archaeology, anthropology, and ecology. It provides a framework for understanding:

• Early human dispersal from Africa into Australasia.
• The evolution of unique species through isolation.
• The impact of sea-level rise on prehistoric human societies.

Modern genetic studies have confirmed close relationships between Aboriginal Australians and Papuans, supporting the theory of a shared Sahul ancestry before geographic separation.