The Twelve Apostles are towering limestone stacks reaching up to 230 feet high, located off the shore of Port Campbell National Park in Victoria, Australia. Scientists from the University of Melbourne have discovered that tectonic plate movements over millions of years lifted and tilted the Twelve Apostles out of the sea. The layered limestone dates back 14 million years, to a time when Earth's temperatures were about 3°C higher than today. The stacks are composed mainly of Port Campbell limestone, deposited during shallow marine conditions millions of years ago.
The tectonic movements did not push up the Apostles perfectly straight; they forced layers to tilt and break, creating small fault lines, according to Stephen Gallagher, the lead researcher. The current sea stacks formed only in the last few thousand years as cliffs eroded, when sea levels rose and coastal erosion by waves undercut cliffs, forming arches that eventually collapsed, leaving isolated stacks. Only eight of the original Twelve Apostles remain, and they are visited by 2.8 million tourists each year. The Twelve Apostles were originally known as the 'Sow and Piglets' on nautical maps.
The study used mapping, microfossil analysis, photographs, digital mapping, samples, measurements of gamma radiation, and analysis of foraminifera fossils to date the rocks. The fossils used for dating were foraminifera, single-celled organisms that evolved, lived, and went extinct at particular times, said Matthew McCurry. The study was published in the Australian Journal of Earth Sciences. The rocks of the Twelve Apostles were forming during the Middle Miocene Climatic Transition, a period of major environmental change and global cooling, according to Erich Fitzgerald. Gallagher noted that 20,000 years ago, Bass Strait was a lake and one could walk to Tasmania, and walk about 70km offshore from the present Twelve Apostles and still be on land.