Shark Bay stromatolites
Shark Bay is located off the coast of Western Australia some 600 km North of Perth. In 1991 it was listed as a World Heritage area because of its endangered species, huge sea-grass beds (the largest in the world), the stromatolites of Hamelin Pool, and its historical significance. These cabbage or domical shaped rocks pictured above are in fact teaming with microbes, including cyanobacteria.
Though the oldest stromatolite in the Pool is not much more than 1,000 years old, the type of microbial communities that build them can be traced back to at least 2.8 billion years old. The shapes can be traced back further – to the 3.5 billion year old stromatolites of the Pilbara where the three basic types are domical, conical and wrinkle.
The Hamelin Pool stromatolites grow extremely slowly. Sometimes they grow as little as 0.04 millimetres a year, and never more than one millimetre. Like the rings in a tree the layers can be dated using the same radioactive Carbon 14 and other techniques.
McNamarra, who wrote a booklet about the stromatolites in 2001, says the organisms are typically 5 micrometres across and can build a structure typically 30 centimetres high and 20 centimetres across. This is equivalent to a human building a structure 105 km high and 75 km across.
To imagine what a microbial mat might be like, think of how your teeth feel before you have cleaned them – that is a microbial mat forming according to Brad BeBout at the NASA Ames Research Center’s microbial mats laboratory and where you can find the excellent animated movie Stromatolite Explorer.
The high salinity of Hamelin Pool is often cited as a reason the stromatolites grow, safe from predators. But this may be misleading, at least in part. Stromatolites grow in other extreme environments like the volcanic pools of Yellowstone National Park, but also in non-extreme environments such as the normal marine environment of the Bahamas. However their occurrence worldwide is still relatively low.
McNamara, K. (1992) Stromatolites, Western Australian Museum, Perth.
Useful web links
About the Shark Bay stromatolites: 
About Shark Bay as a World Heritage area: 
About the Aboriginal History and more about the stromatolites:
At high tide the stromatolites and microbial mats at Shark Bay are submerged. The beach is composed entirely of tiny shells.
Submerged microbial mat
Submerged stromatolites and mats
Submerged smooth mat
At low tide the stromatolites and microbial mats are exposed.
Exposed ripple marks
Pustular microbial mat
Smooth mats between stromatolites
The stromatolites at Shark Bay come in many colours.
Red capped stromatolites
Red and black capped stromatolites
Brown capped stromatolites
White capped stromatolites
The stromatolites at Shark Bay have formed a variety of shapes.
Mushroom shaped stromatolites
Dome shaped stromatolite
Large dome shaped stromatolites
Multi shaped stromatolites
Irregular shaped stromatolites