Research in the Australian Journal of Earth Sciences dates the Victorian coast landmark's limestone to 14 million-8.6 million years ago, using cliff mapping and fossil analysis.
It says tectonic compression lifted the seabed from about 8.6 million years ago, while post-ice-age sea-level rise and wave erosion carved the cliffs and stacks seen today.
The study says the present landscape formed only in the past few thousand years, preserves a detailed Miocene climate record, and remains unstable, with seven stacks generally recognised after recent collapses.
Can science now predict which of Australia's iconic Twelve Apostles will be the next to collapse into the sea?
How can 14-million-year-old rocks provide a blueprint for our planet's fast-approaching climate future?