Sahul is the name given to the single Pleistocene-era continent which connected Australia with New Guinea and Tasmania. At the time, the sea level was as much as 150 meters (490 feet) lower than it is today; rising sea levels created the separate landmasses we recognize. When Sahul was a single continent, many of the islands of Indonesia were joined to the South East Asian mainland in another Pleistocene era continent called "Sunda".
It is important to remember that what we have today is an unusual configuration. Since the beginning of the Pleistocene, Sahul was almost always a single continent, except during those short periods between glacial expansions when the sea level rises to isolate these components into north and south Sahul. The north Sahul consists of the island of New Guinea; the southern part is Australia including Tasmania.
The Sunda landmass of southeast Asia was separated from Sahul by 90 kilometers (55 miles) of water, which was a significant biogeographical boundary first recognized in the mid 19th century by Alfred Russell Wallace and known as "Wallace's Line". Because of the gap, except for birds, Asian and Australian fauna evolved separately: Asia include placental mammals such as primates, carnivores, elephants and hoofed ungulates; while Sahul has marsupials like kangaroos and koalas.
Elements of Asian flora did make it across Wallace's line; but the closest evidence for either hominins or Old World mammals is on the island of Flores, where Stegadon elephants and perhaps pre-sapiens humans H. floresiensis have been found.
Routes of Entry
There is a general consensus that Sahul's first human colonizers were anatomically and behaviorally modern humans: they had to know how to sail. There are two likely routes of entry, the northern-most through the Indonesia Moluccan archipelago to New Guinea, and the second a more southern route through the Flores chain to Timor and then to Northern Australia. The northern route had two sailing advantages: you could see the target landfall on all legs of the journey, and you could return to the departure point using the winds and currents of the day.
Sea craft using the southern route could cross Wallace's boundary during the summer monsoon, but sailors could not consistently see target landmasses, and the currents were such that they could not turn around and go back. The earliest coastal site in New Guinea is at its extreme eastern end, an open site on the uplifted coral terraces, which has yielded dates of 40,000 years or older for large tanged and waisted flakes axes.
So When Did People Get to Sahul?
Archaeologists mostly fall into two major camps concerning the initial human occupation of Sahul, the first of which suggests that the initial occupation occurred between 45,000 and 47,000 years ago. A second group supports the initial settlement site dates between 50,000-70,000 years ago, based on evidence using uranium series, luminescence, and electron spin resonance dating. Although there are some who argue for a much older settlement, the distribution of anatomically and behaviorally modern humans leaving Africa using the Southern Dispersal Route could not have reached Sahul much before 75,000 years ago.
All of the ecological zones of Sahul were definitely occupied by 40,000 years ago, but how much earlier the land was occupied is debated. The data below was collected from Denham, Fullager, and Head.
- Wet tropical rainforests in eastern New Guinea (Huon, Buang Merabak)
- Savanna/grasslands of subtropical northwestern Australia (Carpenter's Gap, Riwi)
- Monsoonal tropical forests of northwestern Australia (Nauwalabila, Malakanunja II)
- Temperate southwestern Australia (Devils Lair)
- Semi-arid regions of interior, southeastern Australia (Lake Mungo)
Today, Sahul has no native terrestrial animal larger than about 40 kilograms (100 pounds), but for most of the Pleistocene, it supported diverse large vertebrates weighing up to three metric tons (about 8,000 pounds). Ancient extinct megafaunal varieties in Sahul include a giant kangaroo (Procoptodon goliah), a giant bird (Genyornis newtoni), and a marsupial lion (Thylacoleo carnifex).
As with other megafaunal extinctions, the theories about what happened to them include overkill, climate change, and human-set fires. One recent series of studies (cited in Johnson) suggests that the extinctions were concentrated between 50,000-40,000 years ago on mainland Australia and slightly later in Tasmania. However, also as with other megafaunal extinction studies, the evidence also shows a staggered extinction, with some as early as 400,000 years ago and the most recent about 20,000. The most likely is that extinction happened at different times for different reasons.
This article is part of the About.com guide to Settlement of Australia, and part of the Dictionary of Archaeology
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