Stromatolites / algae rocks
Dome-Shaped stromatolites living in deep seas, protecting
REEF BUILDING BLUE ALGAE
First Period of Appearance
Stromatolites are the most ancient life form to have left traces. The oldest fossils are 3,5 billion years old.
They form superimposed layers :
- one layer is composed of blue algae (cyanobacteria) using photosynthesis to growth. It grows horizontally during the night and vertically during the day;
- another layer is composed of sediments and other floating particles which have been trap by the next layer of blue algae
These accumulation make structures that are more or less bulbous in the tide zone and are part of today's fossilized reefs of the area. They can be as much as 3 km wide like in the mount Atlas in Morocco.
The stromatolites have created a good part of our atmosphere rich in oxygen and ozone layer, two gas that have allowed the development of more complex life form, by using the C02 and rejecting oxygen.
The paleontologist Thomas Bolton has taken a picture of these construction which dates from the Silurian :
- 420 millions years.
Today, stromatolites are limited to a few areas such as Shark Bay in Australia, where water is very salty (7%) and prevents grazer organism from destroying them. You can also see fossilized remnant of stromatolites next time you go to Gatineau in the Ottawa river bed if the water level is low. You can visit http://geo-outaouais.blogspot.ca/2013/03/stromatolites-exceptionnels-presque.html for more information (French only).