Today’s feature paper in on Bahamas stromatolites, featuring a guest post from
the lead author Rupert Perkins. Lots more information after the jump.
First, some basic information from The Bahamas Marine Ecocentre website….
What are “Stromatolites”?
Stromatolites are a unique and special type of reef. Unlike most present-day reefs, which are composed of coral, stromatolites are formed by microorganisms. The characteristic feature of these microbial reefs is a layered internal structure– indeed, ‘stromatolite’ is derived from Greek meaning ‘layered rock’
Why are Stromatolites important?
Stromatolites are the oldest known macrofossils, dating back over 3 billion years (Earth is ~4.5 billion years old). Dominating the fossil record for 80% of Earth history, they are an important source of information on the early development of life on Earth and possibly other planets. Moreover, scientists believe that the photosynthetic activity of cyanobacteria, the most important group of stromatolite-forming microorganisms, generated the oxygen in our atmosphere. This oxygen allowed the evolution of higher forms of life, including humans!
What is special about Bahamian Stromatolites?
Stromatolites are rare in today’s oceans. However, they can be found in several localities along the margins of Exuma Sound. The Bahamian stromatolites are living relatives of Earth’s oldest reefs. Bahamian stromatolites are unique in that they are the only known examples of present-day stromatolites growing in open ocean conditions, equivalent to those of many 1 to 2 billion year-old Precambrian platforms.
And thanks to Rupert for his summary of the paper….
Roughly 3.9 billion years before present (3.9 BBP), life on earth was very different, in fact it hadn’t even started. The atmosphere was largely composed of harsh gases (reducing gases) such as carbon monoxide, carbon dioxide and methane. Yet in these harsh conditions, life did evolve, and importantly that life evolved into photosynthetic organisms which changed the planet. The production of oxygen by the very first photosynthetic organisms (photoautotrophs) changed the atmosphere and as little as 350 MBP, sparked the evolutionary explosion of the Cambrian Diversification. One set of organisms that first started this process were the cyanobacteria, also known as blue green algae. These are very primitive single celled organisms that can be very common in marine and freshwater habitats. Some of the earliest records of the existence of cyanobacteria come from Stromatolites, simply speaking, humps and lumps of sand grains stuck together in discrete layers by the cyanobacteria inside. Today, almost 4 billion years later, stromatolites still exist, and the only example of marine coastal Stromatolites in the world are in the Bahamas, for example in the Exumas Sound, west of Nassau. Here they form in harsh dynamic coastal areas where sand is suspended in the water column as a source for the cyanobacteria to build the Stromatolite slowly over time. We have been studying stromatolites for some time, and more recently investigated the relative importance of different photosynthetic organisms in their construction by analysing their photosynthetic productivity. We found that both the cyanobacteria and microalgae (diatoms and green algae) are important in stromatolite construction, although results were consistent with the hypothesis that cyanobacteria play the dominant structural role.
A stromatolite sample, cross sectioned to show the white sand grains stuck together by sticky polymers produced by the cyanobacteria. The cyanobacteria can be seen as a clear blue green layer just below the surface. The image shows a sample about 2 cm wide.