Every year, millions of visitors stand at the clifftop lookouts along Victoria’s Great Ocean Road and gaze out at the Twelve Apostles. These towering limestone stacks, rising up to 70 metres above the Southern Ocean, are some of Australia’s most recognisable landmarks.

Yet despite their fame, no-one has ever really understood how they came to be. Until now.

In new research published in the Australian Journal of Earth Sciences, my colleagues and I finally answer that question – and the story involves ancient seas, shifting tectonic plates, and a transformation that began millions of years ago.

A window into deep time

The limestone of the Apostles contains an incredible archive of millions of years of history, and in particular climate history. But it has received relatively little attention from scientists.

Each layer was laid down in shallow seas during the Miocene epoch. This period in Earth’s history, marked by a transition from warm to cool climate, lasted roughly from 23 million years ago to 5 million years ago. Each change from one layer to another represents a change in the local conditions such as temperature, chemistry, or movement of the water.

My colleagues........

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