Complete Pleistocene Stromatolites Colony

Description: The oval to circular structure in these images is an entire stromatolite colony that dates to the Pleistocene, a time when stromatolite was no longer prevalent and abundant. 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. No wonder this that this stromatolite shows the Girvanella-like shape that was a small independent colony, never reaching the large domes of the Proterozoic. The location is now a park with no access to collectors, making this example from an old collection impossible to replace.