dimanche 13 mai 2012

The Stromatolites (Shark Bay)


In June 1954, a group of geologists discovered the stromatolites or ‘living rocks’ of Hamelin Pool which linked life on Earth today, with life on Earth 3.5 billion years ago.
Scientists who have studied fossils of stromatolite, once believed them to have been wiped out by intense competition with newer life forms like ants and animals.
While competition dramatically reduced stromatolites worldwide, 550 million years ago, Hamelin Pool has provided a safe haven for stromatolite colonies for the past 5000 tears.
Stromatolites are layered limestone rock built by single-celled cyanobacteria (blue-green bacteria), which trap and bind sediments. Some build craggy towers, others build flat spongy mats.
At the entrance to Hamelin Pool is a massive sand bar called the Fauré Sill, which has built up over 6000 years and restricted the tide flow into the Pool.
The shallow waters of Hamelin Pool evaporate quickly and create super salty water. In such harsh conditions, few sea snails can survive to graze on cyanobacteria.
Hamelin Pool has become a safe neighbourhood for cyanobacteria which build stromatolites of various shapes and sizes at different water depths.

Red Caps. 
These red-capped stromatolites stopped growing about 500 to 1000 years ago when the sea level fell. The reason for their colouring is a family mystery. It may have been because of iron in the water as they grew or the pigment of visiting bacteria.

Layers of history
Stromatolite layers grow outwards, like the growth rings of a tree. The outer layer remains a thin strip of active life with a sticky film to trap and bind drifting shells and sand. They slowly build up layers which harden into rock.
Scientists believe that the internal growth rings provide information on local environmental changes during the stromatolites lifetime. Some scientists say that the growth rings of very ancient stromatolites reflect changes in the length of days, angle of the sun, even the rate at which the earth rotated.

Living rock
The cyanobacteria that build us first appeared n earth 3.5 billion years ago when oxygen was scarce. As the original stromatolite colonies expanded, they released more and more oxygen into the atmosphere, eventually raising the oxygen level to 20% of all atmospheric gases. This led the way for air-breathing life forms to evolve.
When the tide is in, you can see little bubbles.
It was amazing to see these stromatolites, and to think that we live are alive on earth today is thanks to them is fascinating!
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We spent the night at the Hamelin Bay Station. It was really nice and calm there, and the owners were very friendly. It is in the middle of nowhere though! We wanted to go and buy some food but were told that the closest shop was more than 100km away!

There were some black swans on the lake! 
The black swan is the state emblem, and the Swan River was named after it, but sadly had very few, because most of the swan’s preferred habitat, the shallows, has been destroyed.



Le Carnet de Voyage
(cliquez sur les images pour agrandir)

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