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Earth's longest lifelines


 
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Dr Brendan Burns, from the University of NSW School of Biotechnology and Biomolecular Sciences, takes a closer look at ancient life on Earth, one that produced amazing structures called stromatolites.
Stromatolites are basically living rocks. If you tap on them it is like tapping on concrete but they are alive, formed very slowly over vast periods of time by perhaps the simplest and most ancient forms of life on Earth - bacteria 

 
They are the communal products of these simple single celled life forms to surviving in extreme environments, The microorganisms somehow interact cooperatively in trapping the sediment around them to produce column like structures to help them survive environmental pressures.They look like a large cauliflower and can form to a metre high column (higher they would probably topple over). There are living (as opposed to fossilised stromatolites from millions or billions of years ago) beds of stromatolites in Shark Bay, Western Australia.

 
These beds have formed on intertidal areas within extreme environments due to high temperatures and high salt levels and the stromatolite structures actually help protect the microorganisms inside from that harsh environment.
Western Australia is one of the best places to see modern stromatolites but they are also found in a few other places such as Mexico and The Bahamas. They used to be widespread but have shrunk in their distribution to only the few places mentioned. They are a very popular meal for some higher organisms because they are rich in nutrients and so tend mainly to survive in areas where the extremes of environment protect the stomatolites from predation. The structures take many thousands if not millions of years to form. They grow in layers of less than 1mm a year so they can be dated, just like trees. 
Above and below left: stromatolite images from Shark Bay. Below right: section through stromatolite from WA beds. Images by Brendan Burns

 
The modern stromatolites like the ones at Shark Bay are thousands (perhaps tens of thousands) of years old and, because they are still alive, they are treated as natural living laboratories.
They grow as if in fields about half to a metre apart. These fields can stretch for kilometres, as they do in Shark Bay. There are also ancient or fossilised stromatolites in Western Australia.
The oldest stromatolite in the world was dated as 3.7 billion years old which is incredible given that the earth was only formed some 4.5 billion years ago. 

 
It seems the microorganisms within the stromatolites may respond to random signals from others, which bring about changes that are beneficial to the whole community. This adaptation has allowed these single cell creatures to thrive. One of the main organisms inside them is blue-green algae that produce oxygen through photosynthesis. Indeed it is thought that the very first oxygen that was produced on the planet was by blue-green algae. Such microorganisms are more cooperative and more interactive than we would have thought. The whole is truly greater than the sum of its parts.

It is quite likely our beds of stromatolites would not survive an increase in sea level as a result of climate change so stromatolites are like an environmental dipstick, monitoring the health of our planet. Stromatolites also change our concepts of the boundaries of how life began on Earth because microorganisms are found in all sorts of extreme environments, from high temperature and high salinity in Shark Bay to inside nuclear reactors and under the ice in Antarctica. Without microorganisms like bacteria life would cease to exist on Earth. 

 
These microorganisms utilise different forms of carbon, nitrogen, sulphur and the like, often producing essential substances that neither animals nor plants can. They can also return gases to the atmosphere and remove toxic waste. Bacteria contribute to the nature and balance of things we take for granted like water and the atmosphere. Without their activity the food chain of life would not exist.

 
The fact that microorganisms exist all over the Earth broadens the possibilities of where life might have evolved on Earth. It also broadens the possibilities of life in environments outside of Earth. A lot of stromatolite research is born out of collaborations with NASA. Mars, for instance, has very similar to the environments on early Earth including some very salty areas. NASA now believes that if life is found elsewhere it would most probably be something simple like bacteria. NASA is looking at stromatolites as potential biomarkers for life. Who would have thought that it would be scientists that would truly read our lifelines? 

Dr Brendan Burns was interviewed for A Question of Balance by Ruby Vincent. Images by Dr Burns. Summary text by Victor Barry, October 2016.

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