This
beautiful stromatolite exhibiting classic growth ring structure
is from a locality that people generally associate with trilobites
and other Paleozoic fossil, the Atlas Mountains of Morocco, except
this fossil is 2 to 3 times older. Dating to the Mesoproterozoic,
this 1.0 to 1.2 billion year old stromatolite has various shades
of reddish brown to almost white in irregular, alternating bands.
The unidentified prokaryotic bacteria responsible for this fossil
is likely to be a species of cyanobacteria, the primitive organisms
that largely produced Earth's atmospheric oxygen.
It would take
another 600 million years after this stromatolite was formed before
shelly animals appeared on earth.
The distinct
alternating band structures within stromatolite could signify
temporal variation growth patterns in a large global colony that
resulted from changing conditions in the benthic environment.
The specimen
has been polished to a mirror finish perpendicular to the growth
lines.
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