Stromatolites: Geological or biological?

Hello! I do apologise for not posting in a while but I’ve been swamped by exam study – however I’m finally finished and it feels like a giraffe giving birth, both beautiful and hard to believe. I’ve got heaps of odd organisms for you but I’d like to first reply to a question I received a few weeks back – Stromatolites, are they more geological or biological?

Luckily these are something I already know a bit about because you can find them in Australia, not too far from where I live. So what exactly are they? Stromatolites are colonies of tiny cyanobacteria which layer on top of each other to form structures that look just like ordinary rocks. Except they’re not rocks. They’re alive.

Photo source: Wikipedia commons

To begin with we only knew they existed from some rather old fossils found in the Pilbarra region of Western Australia, and by rather old I mean a casual 3.4 billion years old. It seems that all that time ago these subtle and seemingly insignificant structures dominated the landscapes and are the reason oxygen levels in our atmosphere increased enough to be able sustain the oxygen enthusiastic animals we see today. This is because the cyanobacteria that make up stromatolites acted like plants do today, taking in carbon dioxide and releasing oxygen.

Perhaps what’s most amazing about stromatolites though, is that they still exist 3.4 billion years later. In 1961 living stromatolites were discovered in remote WA locations were conditions are harsh and hostile. These modern day stromatolites were pretty much unchanged from the billion year old fossil evidence meaning these colonies have stayed the same through all this time.

Stromatolites are therefore incredibly important to both the biological and geological world, and while I’d say they’re more biological, I’m probably biased. I don’t think anyone could argue however, that we have a lot to thank from these rocky and robust structures.


Pickrell, J. (2010). Stepping back in time in Western Australia. Retrieved from:

One comment

  1. These are amazing – I’ve been to see them in Shark Bay WA and was totally awed that these are still be around after living so long. And I find it equally cool that they actually grow, albeit very VERY slowly. I’d recommend visiting them if you ever get a chance…who knows what might happen to them when climate change ramps up 😦


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