I love rocks. I notice the sparkly white ones. I am fascinated by the cracks and fissures, the colours and textures. I pause when walking to look at pebbles. I regard myself as quite rock-aware. But these stromatolites were getting me down.
That is until the pebble dropped for me.
I was walking in the veld with the amazing Murray MacGregor, an expert in Karst Landscape. (I suspect that he will say there is no expert on Karst Landscape, only scholars.)
A Karst landscape is an undiscovered land under the land. Usually we are referring to a limestone or dolomite formation. But the critical point is that the rock is water soluble, and is dissolving away under our feet shaping vast caverns, tunnels and systems which link in mysterious ways.
(Readers of Terry Pratchett's novels will recognise Koom Valley as the quintessential Karst Landscape - see "Thud!")
Where there is dolomite and limestone, there likelihood of discovering fossils is high. And would you know it, here we are living on the same stuff as the World Heritage Site (The Cradle of Humankind). But that is not the discussion right now.
In these formations in this region there is a significant layer of rock ( I am of course simplifying hugely - how else will I understand?)
This rock is sedimentary in nature. Meaning this layer was formed by layers and layers of deposits being compacts and pressured. What is especially interesting about this layer is its age (up to 3.5billion years old) and what it contains.
Would you be astounded if I told you this layer of rock - right here under my feet! - contains one of the earliest life forms on this planet? The life form responsible for changing the chemical composition of our atmosphere to include oxygen. We have embedded in the ground a history lesson for life!
This lesson is worth billions. It must be. Some countries spend fortunes building and launching space craft to go and look for the records of the earliest life forms out in space to better understand how life evolved and flourished.
Stromatolites are the fossilised cells of the earliest life form. It is generally accepted (by those in the know) that photosynthesizing single celled prokaryotes were the first life form.
These prokaryotes lived in large colonies. Murray explained in layman's terms how a vast expanse of water, shallow and saline, provided the perfect habitat for single celled life forms millions of years ago. Scientist know this to be true as the see similar formations occurring in Shark Bay Australia (a World Heritage Site) in present day.
They are able to verify assumptions made about the formation of stromatolites by studying this live system.
The simple explanation is that a cyclical process is setup. The duration is indeterminate - daily, weekly, hourly. The algae - large colonies of single celled organisms - formed in "mats". They exchanged carbon dioxide for oxygen, and over a period the carbon dioxide would become depleted. The cells would precipitate calcium carbonate, and this would form a trap. Layer upon layer of organisms would exchange CO2 for O2, become trapped as the cells above became covered in sticky calcium carbonate. The cells repeatedly re-colonised above the sedimentary layer (calcium carbonate) and in the life-giving sunlight, and so formed layer upon layer in a cyclic repetitive process (which is why we see layers in any stromatolite).
Now that I understand the nature of the organism better (and have dropped the notion I had of an algae plant) I recognise that stromatolites are the historic fingerprint of a tough little cell making oxygen to prepare the way for life on this planet.
I also understand that what lies exposed at my feet is rock formed between 2.2 and 3.5 billion years ago. That rock layer is shallow, and now that it is exposed, is being eroded. Like all things, it is being "recycled" and we are custodians of a history lesson for this short time.