Sahul was a vast ancient landmass that once connected modern-day Australia, New Guinea, and Tasmania. This paleocontinent emerged during periods of lower global sea levels, creating a unique prehistoric landscape. Its existence offers a glimpse into a time when geography was dramatically different, shaping the evolution of distinctive life forms and influencing early human dispersal. Understanding Sahul helps unravel the deep history of this region.
The Ancient Continent Revealed
Sahul encompassed what is now mainland Australia, New Guinea, Tasmania, and the Aru Islands, spanning approximately 10,600,000 square kilometers at its greatest extent during low sea levels. This vast landmass was separated from Sunda to its west by the Wallacean Archipelago.
The formation of Sahul resulted from global glacial periods, particularly during the Pleistocene Epoch (about 2.6 million to 11,700 years ago). During these ice ages, large volumes of Earth’s water were locked in continental ice sheets, causing sea levels to drop significantly, up to 131 meters (430 feet). This exposed vast areas of continental shelf, forming land bridges that connected the separate landmasses into a single continent.
Sahul existed as a unified landmass until about 18,000 years ago, when rising temperatures led to melting ice sheets and a gradual increase in sea levels. New Guinea became separated from the Australian mainland approximately 8,000 years ago, and Tasmania about 6,000 years ago, as the land bridges submerged.
Life on Sahul
Sahul hosted a unique array of flora and fauna, distinct from other continents, primarily due to its prolonged isolation. Its varied geography included tropical rainforests in equatorial mountain regions, extensive savannas, and tropical dry forests. Farther south, the climate mirrored modern Australia, featuring a large interior desert, scrublands, and temperate forests along the eastern coast.
The continent was characterized by its distinctive megafauna, with nearly all large mammals being marsupials or monotremes. Notable examples include the Diprotodon optatum, a giant wombat-like creature weighing over 2,700 kg (about 3 tons), making it the largest known marsupial. The powerful Thylacoleo carnifex, or marsupial lion, was a formidable predator, weighing around 100 to 130 kg, and Procoptodon goliah was a 230 kg giant kangaroo. This isolation allowed these species to evolve independently, resulting in unique adaptations within their ecosystems.
Human Journey to Sahul
The first humans to reach Sahul embarked on a remarkable maritime journey across the Wallacean archipelago from Sunda, a region that included modern-day Southeast Asia. Archaeological evidence and modeling studies suggest that humans first arrived in Sahul between 45,000 and 75,000 years ago, with a widely accepted estimate around 65,000 years ago. This migration required multiple open-ocean crossings, some approaching 100 kilometers, indicating advanced cognitive and technological capacities for sea travel.
Archaeologists have considered two primary routes: a northern path through Sulawesi into New Guinea, and a southern path via Bali and Timor onto the expanded shelf of northwestern Australia. Recent research, however, casts doubt on Timor as an early migration route, suggesting human absence there until around 44,000 years ago. Archaeological discoveries, such as those at Mololo Cave in New Guinea and the Madjedbebe site in Northern Australia, reveal early human presence through artifacts and stone tools. These findings, along with rock art in areas like Arnhem Land and the Kimberley, provide insights into the early life and cultural practices of Sahul’s first inhabitants.
Sahul’s Legacy in the Modern World
The geological history of Sahul continues to shape the contemporary geography and biodiversity of Australia, New Guinea, and Tasmania. The separation of these landmasses, driven by rising sea levels after the last Ice Age, resulted in distinct evolutionary paths for species, contributing to the unique biodiversity observed today. The distribution of many plant and animal species across these regions directly reflects their shared ancestry on the ancient continent.
Understanding Sahul provides scientists with a deeper context for interpreting current climate patterns and the ongoing impacts of sea-level changes. The rapid inundation of vast coastal plains offers insights into how past environmental shifts affected human populations and ecosystems. This historical perspective aids in predicting future environmental responses and informs conservation efforts.