Geological study reveals the formation timeline of the Twelve Apostles sea stacks
Consensus Summary
A new geological study of Victoria’s Twelve Apostles, published in the *Australian Journal of Earth Sciences*, has precisely dated the iconic sea stacks’ formation between 16 million and 8.6 million years ago, with the landmass emerging from the ocean 8.6 million years ago. Researchers used microfossils (foraminifera) embedded in limestone layers—including Gellibrand marl and Port Campbell limestone—to reconstruct the region’s history, combining modern fieldwork with unpublished 1960s data. While the stacks themselves are only ~20,000 years old (formed by recent erosion), the cliffs preserve layers from the Middle Miocene Climatic Transition, a period of global cooling that preceded the Ice Ages. The study also notes the Apostles’ fragility, as erosion will eventually collapse them, and highlights their role as archives of ancient marine life, including the peak reign of Megalodon. Both sources agree the actual number of stacks is seven, not twelve, and that the area attracts millions of tourists annually.
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Key details reported by multiple sources:
- The Twelve Apostles' limestone layers formed between 16 million and 8.6 million years ago, with the landmass rising from the ocean 8.6 million years ago.
- The study used microfossils (foraminifera) embedded in limestone to date the rock layers, published in the *Australian Journal of Earth Sciences*.
- The Twelve Apostles are actually seven limestone stacks (not twelve), with erosion forming them in the last 20,000 years as sea levels rose after the last glacial maximum.
- The region’s cliffs include Gellibrand marl (15–16 million years old) and Port Campbell limestone (grey and yellow layers), topped by Hesse clay.
- The study combined previously unpublished 1960s research with modern fieldwork to create the most complete geological timeline of the Apostles.
- The Apostles’ rocks formed during the Middle Miocene Climatic Transition, a period of global cooling that preceded the Ice Ages.
- The research area spans a 17km stretch from The Arch to Clifton Beach, southeast of the Twelve Apostles.
Points of Difference
Details reported by only one source:
- The largest Apostle contains ~760 trillion microfossils, though they are microscopic or fragmented.
- The Drowned Apostles (five submerged stacks ~6km offshore) are ~60,000 years old and were swamped by sea-level rise.
- Australia’s continental plate collided with the Pacific Plate ~11.6 million years ago, contributing to the Otway Ranges’ formation.
- Parks Victoria confirms there are only seven stacks, not twelve, despite the name.
- The study focused on a 40km stretch of continuous cliffs rising up to 80m, with visible sediment layering.
- Matej Lipar (physical geographer) noted the Apostles are ‘fragile archives of past environments’ and erosion will eventually collapse them.
- Stephen Gallagher’s next research step is to reconstruct the climate history of the region in greater detail.
- The Apostles were originally called the ‘Sow and Piglets’ on nautical maps.
- 2.8 million tourists visit the Twelve Apostles annually along the Great Ocean Road.
- The Middle Miocene Climatic Transition was a ‘slide into proper sustained global cooling,’ setting the stage for Ice Ages.
- Megalodon and other large sharks thrived during the Apostles’ formation period (~14–8.6 million years ago).
- Dr. Matthew McCurry (Australian Museum) highlighted foraminifera as a key tool for dating marine rocks.
- Dr. Erich Fitzgerald (Museums Victoria) called the study important for ‘bookending’ the Apostles’ geological timeline.
Contradictions
Conflicting information between sources:
- The ABC states the Gellibrand marl formed ‘from about 16 million to 14.1 million years ago,’ while the Guardian describes it as ‘15 million years old’ without a range.
Source Articles
Ancient fossils reveal when the iconic Twelve Apostles formed
An analysis of tiny fossils of sea creatures found in rock samples around the Port Campbell region in south-western Victoria has refined our understanding of how the Twelve Apostles formed.
‘A history of the Earth’: Twelve Apostles revealed to be as old as 14m years
Tectonic plate movements over millions of years have lifted and tilted the layers, with records of ancient earthquakes in the rocks Get our breaking news email , free app or daily news podcast Microscopic fossils embedded in limestone have helped reveal the true age of Victoria’s Twelve Apostles, as 8.6 to 14m years old. The conclave of giant golden pillars is visited by 2.8 million tourists each year, a highlight for those travelling along the Great Ocean Road south-west of Melbourne. Continue