Here
is very interesting and pretty mid-Proterozoic stromatolite from
near Beijing, Peoples Republic of China. The oval to circular,
darker reddish-brown structures in the matrix are bacterial fossil
nodules, referred to as Baicalia sp. These may be what are commonly
called algal balls, formed by separate colonies of prokaryotic,
photosynthetic bacterial, e.g., likely to be cyanobacteria, the
primitive organisms that largely produced Earth's atmospheric
oxygen. Alternatively, the distinct structures within the stromatolite
could signify temporal variation of growth patterns in a large
global colony that resulted due to changing conditions in the
benthic environment.
The
beautiful specimen has been polished to a mirror finish perpendicular
to the colonies on the side shown.
Baicalia
sp. is a putative bacteria believed to have been photosynthetic
prokaryotes that oxidized ambient iron and other heavy metals
as part of their metabolic pathways. The presence of the metals
such as iron for precipitation is tangible evidence that Precambrian
times had extensive volcanic activity.
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