Sea stacks, that is pillars of rock which seemingly jet out from the ocean, often near the coastline, are a spectacular site to see around the planet. While many of these beautiful features are in of themselves tourist attractions, few compare to the spectacular nature of one of the most visited attractions along the Great Ocean Road in Australia, the 12 Apostles. Despite their name, there are not 12 sea stacks in the 12 Apostles, but rather 9 limestone rich pillars. These pillars are up to 50 meters or 164 feet tall, and tower in a near vertical manner above the cliff walls adjacent to the Southern Ocean. While the section of Port Campbell National Park which the 12 Apostles are in is quite spectacular, it is not the only local feature as erosion has carved away several regional features which will probably form future apostles in addition to a large series of cliffs adjacent to the ocean. The 12 Apostles geologic formation is located in the southern portion of the Australian state of Victoria where it is 10 kilometers east southeast of the city of Port Campbell. While several similar sea stack formations involve rock formations which are 50 million years in age or older, the rock formation which makes up the 12 Apostles is far younger. As, the rock formation found in the 12 Apostles originated between 14 and 8 million years ago, with the relevant rock unit which composes them being known as the Port Campbell Limestone. Like many other limestones, this feature is highly organic in origin, being composed in part of the remains of many millions of ancient sea creatures. Limestone can form without the aid of hard shelled creatures which have calcium carbonate shells, but before such creatures appeared in the vast oceans, limestone formations were incredibly rare. This limestone unit is underlied by a more silty and muddy rock type known as the Gellibrand Marl, which when combined present a story about the last 15 million years at this very location. Approximately 15 million years ago, what is now the site of the 12 Apostles was the site of a greatly expanded ocean which reached several kilometers inland from its modern appearance. Sea levels at the time were unusually high, being about 30 meters above modern levels. In this environment, large amounts of marl were slowly deposited over time, creating the base of the 12 Apostles and regional cliffs. The sea level eventually then got another 30 meters higher, and the region became a pristine environment for coral reefs and numerous shell bearing ocean creatures such as molluscs. As these creatures and corals died, and calcium carbonate precipitated to the ocean floor, layers of limestone quickly built up. This process continued for 6 million years until a 50 meter thick rock unit of limestone had been constructed. By this time, the sea level had decreased by 30 meters, and what was once a coral reef became a large cliff face with blocks of limestone and marl. Slightly acidic rainwater had over time carved into sections of the basic limestone, forming large cracks. Over time, cracks widened into crevasses, and preferential erosion created a series of towering vertical pillars with a fresh layer of clay at their top. This clay was subsequently eroded away, which in addition to parts of the near vertical cliff walls eroding, formed a series of sea stacks which tower above the ocean in their modern appearance. However, the 12 Apostles will not last forever, as in 2005 one of the 9 sea stacks collapsed, becoming a pile of rubble. This is the same fate which eventually awaits all of the other sea stacks, but this is simply to be expected over the next several million years. More apostles will eventually form as others are destroyed. Thanks for watching! If you would like to request a specific topic, please leave a comment below. Additionally, I would like to thank Amie Z for increasing their patron tier on this channel's patreon page!