Metre-high knobbly columns of layered rock in shallow water, living stromatolites, built by cyanobacteria trapping sediment…Metre-high knobbly columns of layered rock in shallow water, living stromatolites, built by cyanobacteria trapping sediment, and the closest thing on earth to what life looked like for the first three billion years. Only a handful of marine sites in the world still have them growing. Stromatolites dominated the planet's oceans for over two billion years and produced the oxygen that made complex life possible. They vanished almost everywhere once grazing animals evolved; the Exuma colonies survive because the fierce tidal current in the cuts keeps grazers off. Shark Bay in Australia is the only comparable site. Anchorage: Berth at Highbourne Cay marina or anchor on the bank side; the formations are on the ocean-side beach rock. Hazards: Strong tidal current on the ocean side. Never stand on or touch the stromatolites, they grow at a fraction of a millimetre a year. More