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Brand new 3.7 billion years old stromatolites

One of the most ancient forms of life on the planet might be more common than we thought.

How can something that’s almost four billion years old be brand new? Plainly, that’s a ridiculous statement (and it’s either piqued your interest and you read on, or turned you away, so you leave that much the poorer because you’ve missed the news I’m about to share…). But it reflects a newly-discovered site of a biological phenomenon that’s been known on planet Earth for over three and a half billion (that’s thousands of million) years.

 Stromatolites growing in Hamelin Pool Marine Nature Reserve, Shark Bay in Western Australia
Stromatolites growing in Hamelin Pool Marine Nature Reserve, Shark Bay in Western Australia. Photo: Paul Harrison / Wikipedia

The structures are stromatolites[1,2], which are “layered mounds, columns, and sheet-like sedimentary rocks” created by the biological activity of cyanobacteria[3,4]. Cyanobacteria, as all plant-minded people should know, are bacteria but which photosynthesise in a similar way to green plants – i.e. they use water, CO2 and sunlight to create organic compounds and oxygen. This so-called oxygenic photosynthesis has been widely proposed to be one of the main routes whereby oxygen got into the early Earth’s atmosphere and accumulated there over the course of hundreds of millions of years. This led to the Great Oxygenation – or Oxidation – Event (GOE – Richard Blaustein) which has been implicated in providing the permissive environment for development of more complicated lifeforms such as animals (i.e. plant-like organisms enabled the development of animals – how phytochauvinistically pleasing is that!?)*.

The only place I knew you could find living stromatolites was in the sea in the intriguingly-entitled Shark Bay in Australia. Now, these ‘living fossils’ have been found in Tasmania (Australia), in karstic wetlands, a freshwater habitat. Presciently, the article’s abstract concludes with this interesting statement: “Our findings constitute a novel habitat for stromatolites because cool-temperate freshwater wetlands are not a conventional stromatolite niche, suggesting that stromatolites may be more common than previously thought.” As the oldest evidence for life on Earth, these biological entities hold a special place in the planet’s natural history and rightly Shark Bay is a UNESCO World Heritage site. Will the Tasmanian site now join its marine counterpart in sharing that exalted status? Or will so many other stromatolite sites be found that they’ll be considered commonplace and treated with the usual contempt humans reserve for the ‘abundant’, and probably destroyed..?

* Somewhat ironically, the decline of stromatolites in the fossil record has been linked to the appearance of grazing metazoa – multicellular animals life forms, whose evolution and development may have been aided and abetted by the oxygen produced by the cyanobacteria’s photosynthetic endeavours. So, here is today’s Philosophical Botany exam question: Stromatolitic cyanobacteria, architects of their own downfall? Discuss…

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