LIVING REPRESENTATIVES OF THE MOST ANCIENT ORGANISM
The rocks in the hyper-saline waters of Lake Thetis are not quite what they seem. They are actually living things. Stromatolites, are the oldest living lifeforms on our planet.
Stromatolites are formed through the activity of primitive unicellular organisms: cyanobacteria (blue-green algae) and other algae. These grow through sediment and sand, binding the sedimentary particles together, resulting in successive layers which, over a long period of time, harden to form rock. For at least three-quarters of the earth’s history stromatolites were the main reef building organisms, constructing large masses of calcium carbonate.
However their most important role in the history of the earth has been that of contributing oxygen to the earth’s atmosphere. When stromatolites first appeared on earth about 3.5 billion years ago there was little or no oxygen in the atmosphere. The organisms which construct stromatolites are photosynthetic. They take carbon dioxide and water to produce carbohydrates, and in doing this they liberate oxygen into the atmosphere. It has been speculated that bacteria found in these organisms were responsible for increasing the level of oxygen in the atmosphere on earth from much less than 1% to the present day level of 21%. It was through the oxygen-generating activity of stromatolites that other animal life on earth was able to develop. These amazingly persistent living fossils form complex microbial communities. Conversely, it is believed that the decline in numbers of Stromatolites is related to the evolution of animals that consumed cyanobacteria and algae. Most living animals, which feed on the bacteria and algae of which Stromatolites are composed, cannot tolerate the extremely saline conditions of places such as Lake Thetis, and as a result Stromatolites can grow here successfully, undisturbed.
Stromatolite fossils are evidence of the earliest life on the earth. Western Australia perhaps has the best Stromatolite fossils, giving a record through the eons of time. Fossils of the earliest known Stromatolites, about 3.5 billion years old, are to be found near Marble Bar in the Pilbara
Stromatolites represent what is seen to be the biggest continuous biological lineage known in the world. The evolutionary events of the last 600 Million years were the time when most of the major groups of animals and plants on earth evolved. If we look very closely they are primitive-celled organisms; these organisms have remained virtually unchanged during the comings and goings of all the animals and plants that have ever lived. Not only have they been found in some of the oldest rocks on earth, they have persisted with no other life forms for company. The existence of these ancient rocks extends three-quarters of the way back to the origins of the Solar System. These amazingly persistent living fossils form complex microbial communities. The long period of time over which these fossils have survived is amazing and these simple organisms have no peers.
The organisms existence is preserved in rocks by their fossilized remains, but also more commonly by the structures they created, domes or columns of sediment called Stromatolites. They come in many shapes and sizes. It is extremely remarkable that the living Stromatolites are only in a small number of places throughout the world. It is known that in the period from one million to three billion years ago, Stromatolites were prevalent on the shores of lakes and seas around the world. Such structures are still being formed today. Cervantes is one of several such sites in Western Australia where you can view them easily. Stomatolites grow as layers of sediment that has been trapped. These layers or mats slowly build on top of each other over many years with each Stromatolite formation only growing at a rate of 5 cm in 100 years! They need light so are limited to shallow water where the sunlight can penetrate.
Our local Lake Thetis with double the salinity of the sea is accessible to view 1.3km down the unsealed Hansen Bay Road, on the way out of town. There is a walkway all around the Lake and also a viewing platform. Please respect this area as it is very precious.
Pinnacles Visitor Centre Freecall 1800 610 660 www.visitpinnaclescountry.com.au. For further Stromatolite information contact D.E.C. 96527 043
Just over 1km from the centre of town (off the Hansen Bay Lookout Rd) lies Lake Thetis. It is estimated the lake became isolated from the sea about 4800 years ago when sea levels dropped and coastal dunes formed around the Lake.
The lake is one of only a few places in the world with living marine stromatolites, or 'Living fossils'. The microbes that build stromatolites are a species of cyanobacteria and are similar to those found in 3500 , which are the earliest record of life on Earth. The lake's stromatolites that look like rocky lumps have been dated to about 3370 years old. Stromatolite communities grow as the this layer of bacteria on their surface deposit calcium, cementing sediment into bulbous structures. Blister mats of cyanobacteria can also be found growing on the margins of the lake in the flood zone. These mats are sensitive and easily disturbed.
The stromatolites are easily accessible during the drier months when the water level is at its lowest. The best examples can be found at the south-western edge of the shoreline but they are brittle and visitors are asked to look, but don.t touch.
Lake Thetis is isolated from major surface drainage and is fed by groundwater flow. The only loss of water comes from evaporation. It is a saline lake but there is no evidence to suggest the lake has a connection to the sea. The water level fluctuates around average sea level but doesn't appear to reflect tidal variations. The lake levels follow trends more closely related to the rainfall for the area.
The lake water is alkaline and nutrient poor but provides an ideal environment for bottom dwelling microbial communities. The lake contains some small fish, amphiods and a few crustacean species adapted to living in highly saline environments.
The circumference of the lake is only 1.2 kilometres and provides an interesting and enjoyable walk. Please stay on the path provided. Enjoy an easy 1.5km loop walk around Lake Thetis and gain an insight into what life was like at the dawn of time.
Like the famous stromatolites of Hamelin Pool, in Shark Bay, these rock-like structures on the edge of Lake Thetis are built by micro-organisms too small for the human eye to see. Within the structures are living communities of diverse inhabitants with population densities of 3000 per square metre!
The thrombolite-building micro-organisms of Lake Thetis resemble the earliest forms of life on Earth. The discovery of modern examples helped scientists to understand the significance of micro-organisms in the environment and unravel the long history of life on Earth. Today living examples of these once completely dominant organisms are restricted to only a few places.