Description:
Stromatolites are remnants of the most ancient of colonial organisms.
Stromatolites are fossils that are the result of the work of
simple blue-green “algae” or Cyanophytes, which lived
in chains or mats covered in a jellylike substance. By taking
in carbon dioxide as a food source, the precipitate limy deposits
on the jelly that builds up in layers. Thus these organisms build
up stony supports for their colonies. These mound like structures
can be anywhere from several centimeters to several meters in
height. The production of oxygen is thought to have led to the “rusting
of the seas” which brought about deposition of extensive
iron deposits such as the Mesabi Range. Stromatolites have persisted
to the modern day in such places as Shark Bay, Australia where
they continue their billions of years old lifestyle. The oval
to circular structures in these images is an entire stromatolite
colony that dates from the Pleistocene, a time when stromatolites
were no longer prevalent and abundant. This is an oncolite, an
unusual type of stromatolite. Oncolytic stromatolites are spherical
rather than domal in nature and are formed around a growth nucleus
such as a shell fragment or even a grain of sand. By the Cambrian,
photosynthetic bacteria responsible for the biogenic formation
of stromatolite structures no longer had the earth to themselves.
The oxygenated atmosphere had become toxic to some bacteria,
and they had to compete with other organisms, some of which would
have been predaceous to this most ancient of life forms. This
specimen comes from the most iconic of locations for stromatolites:
Shark Bay in Western Australia. You cannot help but see Shark
Bay pictured in any TV show that talks about stromatolites. The
location is now a park with no access to collectors, making this
example from an old collection impossible to replace.
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