Located within a sheltered bay on the coast of Western Australia, theb Hamelin Pool Marine Nature Reserve appears at first glance to be a regular rock-strewn beach, though the rocks look kind of odd. Those rocks are not actually rocks. Rather, they are active colonies of one of the first life forms on our planet.
They are called “stromatolites”, and they are made by a single-celled organism know as “cyanobacteria”. Previously known as blue-green algae, cyanobacteria exist since about 3500 million years ago, well before the existence of any other complex life form. They are the oldest type of photosynthetic organism in the world, so old, in fact, that they predate plants by a couple billion years, and provided the earth with most of the oxygen in the atmosphere necessary for supporting subsequent life forms.
Additionally, cyanobacteria are the earliest and were, for three-quarters of the earth’s history, the main reef-building organism, thanks to their peculiar stromatolites. They are formed using sediment trapped in the sticky cyanobacteria’s mucosal secretions, which is then cemented with calcium carbonate produced by the tiny organism. With a colony of millions of bacteria carrying out this process, the stromatolite grows over time at a rate of approximately 0.5mm per year.
Some structures are pillars up to 1.5 metres high and have taken thousands of years to grow. In the Marble Bar area of Western Australia there are fossil stromatolites approximately 50 metres high and 30 metres diameter.
While stromatolite fossils, some of them 3.5 billion years old, have been found around the world, the stromatolites of Hamelin Pool were the first living specimens ever discovered. Discovered by surveyors working for an oil exploration company in 1956, living stromatolites are extremely rare, known to exist in only a small handful of places in the entire world, including an underwater site 6 metres deep in the Caribbean, Persian Gulf, and in the Great Salt Lake of Utah. Hamelin Pool contains the most abundant and diverse collection of living stromatolites, thanks to the hypersaline water (twice the salinity of normal seawater) that allows the cyanobacteria to thrive and keeps would-be predators at bay.
Moreover, the Australian stromatolites are also the easiest to observe, thanks to the clear, shallow water and boardwalk that has been built out into the water, allowing visitors to see the ancient formations without disturbing their habitat. There is also a museum in the nearby Historic Hamelin Pool Telegraph Station that includes an aquarium containing the only living stromatolite in captivity in the world.
Images from Wikipedia