Scientists have determined that Victoria’s Twelve Apostles are between 8.6 million and 14 million years old, far older than the sea stacks visible today, which formed only in the past few thousand years through coastal erosion.
The age was established by analysing microscopic fossils embedded in the limestone cliffs, particularly foraminifera — single-celled organisms whose evolutionary timelines allow precise dating of rock layers.
Research published in the Australian Journal of Earth Sciences combined 1960s fieldwork with modern techniques including gamma radiation measurements, digital mapping, and fossil analysis to build the most complete geological timeline of the site to date.
The study focused on a 17-kilometre stretch from The Arch to Clifton Beach, revealing that the limestone and underlying marl layers were deposited as Australia drifted northward after separating from Antarctica around 30 million years ago.
Tectonic forces tilted and fractured these sedimentary layers over millions of years, creating the angled strata and small faultlines visible in the cliffs today — evidence of ancient earthquakes.
While the rock foundation is ancient, the iconic sea stacks themselves are geologically recent, sculpted by wave action in the last few millennia as the coastline retreated.
Lead researcher Stephen Gallagher of the University of Melbourne noted that the sea stacks represent “the tiny last minute” in a multi-million-year story, contrasting the fleeting nature of the formations with the deep time encoded in the rock.
He added that only 20,000 years ago, Bass Strait was a freshwater lake, allowing travel from the mainland to Tasmania — meaning visitors could have walked 70 kilometres beyond the current Twelve Apostles and still been on dry land.
The largest of the Apostles contains approximately 760 trillion microfossils, with Gallagher observing that “almost every grain in these limestones is a fossil,” though most are too small or fragmented to see without magnification.
These findings not only clarify the region’s geological evolution but likewise provide a valuable climate record, as the fossil assemblages reflect shifts in ocean conditions during the Miocene epoch.
The results underscore how surface landscapes can mislead: what appears timeless and eternal is often a transient feature overlying vastly older foundations.
How old are the Twelve Apostles really?
The Twelve Apostles’ limestone and marl layers are between 8.6 million and 14 million years old, based on fossil dating, while the visible sea stacks formed only in the past few thousand years due to erosion.
Why do the cliffs look tilted if the rocks were laid down horizontally?
Tectonic plate movements lifted and tilted the originally horizontal sedimentary layers over millions of years, creating the angled strata and faultlines seen in the cliffs today.
