Escape

When we talk about Sahul, we are talking about "Greater Australia." For most of the last 2 million years, Australia wasn't an island continent—it was a massive super-island that included New Guinea and Tasmania.

1. What was Sahul?

Sahul is the name given to the combined landmass that existed during periods of low sea levels (the Pleistocene ice ages).

The Land Bridges: During the Last Glacial Maximum (about 20,000 years ago), sea levels were roughly 120 meters (400 feet) lower than they are today.

The Connection: This exposed the Sahul Shelf, creating a vast dry plain where the Arafura Sea, the Gulf of Carpentaria, and the Bass Strait are now. You could have walked from Hobart all the way to the highlands of New Guinea without getting your feet wet.

The Landscape: It wasn't just a bridge; it was a massive savanna and forest system. Central Sahul featured a giant inland lake (now the Gulf of Carpentaria).

2. The First "Mariners"

Sahul is famous in human history because it was the destination of the first great maritime migration.

Crossing the Gap: Humans arrived in Sahul at least 65,000 years ago. Even at the lowest sea levels, Sahul was never connected to Asia. Migrants had to cross Wallacea (a chain of deep-water islands) using sophisticated watercraft.

The "First Contact" Point: Most research suggests the first people landed on the expanded northwestern coastline (near the modern-day Kimberley or Arnhem Land) or via the northern route into New Guinea.

Super-Highways: Once they arrived, these First Nations people mapped out "super-highways"—optimal routes across the continent that followed water sources and manageable terrain.

3. The Biological Wall

Because Sahul was isolated by deep ocean trenches for tens of millions of years, it became a biological "fortress."

The Wallace Line: This is a famous invisible boundary in the ocean. To the west (Sunda/Asia), you find tigers, elephants, and monkeys. To the east (Sahul), you find marsupials (kangaroos, koalas), monotremes (platypus), and birds of paradise.

The Lydekker Line: This marks the absolute eastern edge of the transition zone, specifically where the Australian-origin fauna completely dominates.

4. The "Big Flood"

The Sahul continent "died" about 8,000 to 10,000 years ago when the ice caps melted and the sea rose.

Lost World: Roughly 2 million square kilometers of land—about one-third of the continent—was swallowed by the ocean.

The Split: Tasmania was cut off first (forming the Bass Strait), followed by New Guinea (forming the Torres Strait).

Archaeological Mystery: Because the first humans lived on the coastlines for 50,000 years, many of the most important early human sites are now 100 meters underwater on the continental shelf.

Sahul at a Glance

Feature During the Ice Age (Sahul) Today (Australia)

Landmass Australia + New Guinea + Tasmania Australia (Mainland)

Total Area ~10.5 million km2 ~7.7 million km2

Lowest Point Arafura Plain (Dry land) Arafura Sea (Ocean)

Key Life Megafauna (Diprotodon, Thylacoleo) Modern Australian Wildlife

For a long time, Argoland was one of geology's greatest "missing person" cases. Around 155 million years ago (Late Jurassic), a massive piece of land—roughly 5,000 km long—broke away from Northwestern Australia and seemingly vanished.

In late 2023, scientists finally "found" it, revealing a much more complex story than a single sliding continent.

1. The Breakup (Late Jurassic)

155 million years ago, the supercontinent Gondwana was splintering. Argoland was a fragment of the Australian margin that began to drift north toward Southeast Asia.

The "Argoland Void": Geologists identified a deep-ocean basin off the coast of Western Australia known as the Argo Abyssal Plain. The shape of this basin acted like a "fingerprint," proving that a massive chunk of continental crust had once been attached there.

The Separation: As it pulled away, it left behind the oldest oceanic crust surrounding Australia today.

2. It Wasn't a Solid Continent

One of the reasons Argoland was "lost" for so long is that researchers were looking for one big block of land. Instead, Argoland was a "Argopelago."

Fragmented Land: Even before it fully separated from Australia 155 million years ago, the land was already stretched and broken into a series of micro-continental fragments and narrow ocean basins.

The Disappearance: As it drifted north, these fragments didn't stay together. They became "shattered" and eventually ended up as parts of modern-day Myanmar and Indonesia (specifically Java, Sulawesi, and Borneo).

3. The 155 MYA Environment

Back then, the Northwestern coast of Australia (where the Kimberley and Pilbara regions are now) looked very different:

Tropical Transition: Unlike the cool polar forests of South Australia/Antarctica, Argoland was at a lower latitude. It was likely a tropical or sub-tropical environment.

Marine Life: The rift that formed between Australia and Argoland created a new seaway. This area was teeming with Jurassic marine life, including Ammonites and large marine reptiles like Ichthyosaurs.

The Landscape: Volcanic activity was intense along the rift line as the Earth’s crust was pulled apart, creating a skyline of fire and smoke along the new coastline.

4. Why the Discovery Matters

Finding the remains of Argoland in Southeast Asia solved a major "tectonic gap." It explains:

Biodiversity Lines: It helps explain the Wallace Line, the faunal boundary that separates Asian and Australian species.

Ocean Circulation: Understanding how these landmasses moved helps scientists model how ocean currents changed, which influenced global climate 150 million years ago.

Fast Facts: Australia vs. Argoland

Feature Northwestern Australia Argoland (The Fragment)

Status 155mya Main Gondwana Margin Breaking away

Modern Location Western Australia (Pilbara/Broome) Fragmented in Indonesia & Myanmar

Geology Ancient Cratons Highly deformed "ribbons" of crust

Key Life Early dinosaurs & ferns Marine invertebrates & tropical flora

Around 115 million years ago (during the Early Cretaceous period), Australia and Antarctica were still physically joined together as part of the dwindling supercontinent of Gondwana.

This wasn't the frozen wasteland we know today. Instead, it was a lush, forested world that existed near the South Pole, creating a unique environment for prehistoric life.

1. The Great Separation

During this era, the two continents were beginning a slow-motion "breakup."

The Rift Valley: A massive rift system—similar to the modern East African Rift—was tearing the land apart. This formed a deep valley between what is now Southern Australia and East Antarctica.

The Southern Ocean's Birth: While they were still connected, the crust was thinning and sinking. Shallow seaways began to flood the rift, though a solid land bridge remained near Tasmania for tens of millions of years longer.

Volcanic Activity: The stretching of the Earth's crust triggered significant volcanism along the rift, particularly in the Otway and Gippsland Basins of Victoria, Australia.

2. A "Polar" Greenhouse

Even though these landmasses were located within the Antarctic Circle, the Earth was in a "greenhouse" phase.

The Climate: There were no permanent ice caps. Instead, the region experienced cool, temperate conditions. Summers were mild, but winters involved months of total darkness due to the high latitude.

The Vegetation: The landscape was dominated by Ginkgoes, Cycads, and Conifers (like the ancestors of the Wollemi Pine). In the undergrowth, ferns and mosses thrived in the damp, river-heavy rift valleys.

3. The Dinosaurs of the Dark

The most fascinating aspect of 115 million years ago is the wildlife that evolved to survive the long, dark polar winters.

Leaellynasaura: A small, bipedal herbivore known for having exceptionally large eyes (likely to help it forage in the months of winter darkness) and a very long tail.

Koolasuchus: One of the last "giant amphibians." While crocodiles were kept away by the chilly winter temperatures, this 5-meter-long, ton-heavy carnivore thrived in the cold Victorian rivers.

Cryolophosaurus: Though slightly earlier than 115mya, its lineage represents the types of large theropods that roamed the Antarctic forests.

4. Where to find the evidence today

If you want to see the "scars" of this connection today, you can look at two specific spots:

Dinosaur Cove (Victoria, Australia): The cliffs here are made of the sediment that filled the rift valley 115 million years ago.

The George V Coast (Antarctica): The rocks here perfectly match the geology found in South Australia, like two puzzle pieces that were finally pulled apart.

Comparison: 115 MYA vs. Today

Feature 115 Million Years Ago Today

Connection Joined as Gondwana Separated by ~3,500 km of ocean

Climate Cool Temperate / Seasonal Polar Desert / Ice Cap

Vegetation Lush Conifer Forests Virtually None (Lichens/Moss only)

Daylight Polar Day/Night cycles Polar Day/Night cycles