Geological
Time: Early Cretaceous (135 mya)
Size (25.4
mm =1 inch): 160 mm by 120 mm (maximum)
Fossil Site:
Windalla Radioarite, Kennedy Ranges, Western Australia
Fossil Code:
AS14002
Price: Sold
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 Early
Cretaceous, and thus coexisted with the dinosaurs. 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. |
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