Living Rocks
Thrombolites, ‘living rocks’, are the most common form of microbialites, which are rock-like structures built by micro-organisms. One of the few places in the world where the thrombolites grow is at Lake Clifton in Western Australia’s Yalgorup National Park which is located 32 kilometres south of Mandurah. The lake is also one of only two sites known where microbialites occur in water less salty than seawater. The lake contains the largest lake-bound microbialite reef in the southern hemisphere which is over 6kms long and widens in parts to 120m. The thrombolite structures reach heights of up to 1.3m.
How It All Began
Millions of years ago, earth, as we know it was a little different, there was no oxygen in the atmosphere and there was no protective ozone layer. Scientists believe that things began changing when tiny organisms started to appear (from where no one knows). These tiny little organisms lived in water and produced oxygen. This oxygen entered the atmosphere and over time created the atmosphere we live in today. Now, this process didn’t happen overnight, the organisms had to produce large quantities of oxygen over a long period of time before earth could sustain life . One of the ancestors of these tiny organisms are in fact algae, yes those aquatic plants. Stromatolites and Thrombolites are created by algae and represent the earliest record of life on earth.
What Are Thrombolites?
Thrombolites are formed when the micro-organisms photosynthesize. During this process, they are able to precipitate calcium carbonate from the waters of the lime-enriched lake to form the rock-like structures. Luckily Lake Clifton has an abundance of fresh groundwater which is high in calcium carbonate providing the perfect environment. Thrombolites form in a different way than stromatolites which are found in Hamelin Pool at Shark Bay. Thrombolites have an internally clotted texture, while stromatolites have a layered (laminated) internal structure and are formed by blue-green bacteria trapping sediment particles. Thrombolites and stromatolites were the only known form of life on Earth some 350 to 650 million years ago. Microbes found in both thrombolite and stromatolite formations are believed to be responsible for oxygen production which allowed life to exist on the planet. Thrombolites are the most common form of microbialites and are formed by a variety of micro-organisms. They grow at an average of 1mm a year.
The only place on earth where both marine stromatolites and thrombolites exist is on a small private island, Highborne Cay, in the central Bahamas. 
