Iconic Stromatolites from Shark Bay

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 Pleistocene, a time when stromatolites were no longer prevalent and abundant. 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. This specimen comes from the most iconic of locations for stromatolites: Shark Bay in Western Australia. You cannot help but see Shark Bay pictured in any TV show that talks about stromatolites. The location is now a park with no access to collectors, making this example from an old collection impossible to replace.