Stromatolites
This little piece of rock over here is without doubt a product of living organisms. It is a stromatolite, and it is the oldest fossil we have.
What do you notice?
Hover over me for the answer.
it is laminated rock
A microbial mat community has formed the layers. This community conisted to a
great part out of cyanobacteria. These bacteria form filaments as seen in the picture.
Stromatolites are not true fossils. They do not
contain preserved body parts nor impressions. They consist only of layered sediment.
Fine silt sticks to the aforementioned filaments. In addition, the bacterial mat deposits calcium
carbonate. After a certain period the sediment and the calcium carbonate take away so much light
so that the cyanobacteria do not retain enough light for photosynthesis. What is the answer of the cyanobateria to this situation? They
send new filaments up through the accumulated sediment, creating a new mat. Another sediment layer
then begins to accumulate. In this way, many thin layers of sediment form.
Later, the filaments usually decay so that only the sediment layers remain.
How did such a microbial mat look like? That is shown over here on this information panel. On top of each cylinder lies such a microbial mat. How do we know this? We know, because stromatolites exist up to these days. The site where they are living is Shark bay in Australia. Over there the circumstances are so heavy that only this microbila mats can survive.
The mats grow out to pillars. In between the pillars also sediment is formed. Eventually a solid limestone rock is formed. In the photo beneath: limestone rock where the the pillars are visible , and the interstitial sedimentary rock.
