Stromatolites with Small Girvanella Form
from Nevada Area 51
Time: Lower Cambrian
mm = 1 inch): 5.7 by 4.7 inches maximum
Site: Carrea Formation, Racheal, Nevada; adjacent to Area 51
is stromatolite has a most unusual form genera. It is essentially
filled with concentric spheroids called Girvanella that are commonly
called algal balls. Coming from a Lower Cambrian formation, these
stromatolites date to a time when stromatolites were no longer
prevalent and abundant on earth. The massive cyanobacterial stromatolite
reefs of the Proterozoic had yielded to new reef systems with
abundant and diverse life forms. For more than two billion years
the cyanobacteria had oxygenated earth’s atmosphere through
their photosynthetic, autotrophic metabolism. Earth was now hostile
to them in many ways, with other heterotrophic, eukaryotic microbes
to compete with or be eaten by, and the atmosphere that they had
created was essentially poison to them.
cannot say for sure that the microbes that produced these Girvanella
were cyanobacteria. Perhaps they were plant-like eukaryotic algae.
What seems probable is that each little spheroid was once an independent
colony that was never able to grow into the large domal structures
like those of Proterozoic-time.
locality is another interesting aspect of these stromatolites.
It comes from a small pod between two Ollenelus trilobite zones
immediately adjacent to Area 51 near Racheal, Nevada. As we know
the secrets of Area 51 are as prominent as the uncertainty of
the stromatolites’ makers.