Is this how fossils happen?

16 November 2015
Is this how fossils happen?

By Fran Southgate

Wetlands Landscape Officer

Yesterday I had the pleasure of showing someone from the World Wildlife Fund around some of our rarest and most unique chalk streams in Sussex. These hidden gems are tucked away in miniature valleys which have an almost Jurassic feel to them - all emerald and glistening with tumbling ferns, mosses and liverworts. The water which flows through these small valleys is crystal clear, bubbling straight from hidden aquifers underground, many of which are Jurassic relics in themselves.

The trip was a pleasure not just because I was spending time in these tranquil little enclaves of wildlife, but mainly because I was able to elicit this reaction from a seasoned ecologist by showing her one of the many wonders that inhabit these streams. In the picture, I have just picked up an inconspicuous looking little rock, and snapped it in half to reveal a semi fossilized twig inside. Imagine the reaction that you could get from a child who never gets outs into the countryside.

You could easily walk past these ‘young fossils’, assuming them to be like any other pebble or rock. In fact they are the product of a unique chemical reaction which occurs when the chalk in the water is exposed to oxygen and microbes. The carbonate material in the water solidifies, leaving behind it a kind of porous natural concrete which can encrust or encase anything that it touches. The ‘concrete’, otherwise known as tufa, can calcify around living and dead organisms, creating a solid shell and creating sculpturesque waterfalls and rock features. Sometimes it literally covers the stream bed, making it appear as if someone has indeed poured concrete into the riverbed. I have seen whole snail shells enrobed in tufa, wrapped up like little concrete Christmas presents.

This particular chalk stream is one of my favourites in Sussex. Hanging in a forgotten valley, the landowners are dedicated to preserving these wonderful features as part of a legacy for children and future generations, not as a fossilized landscape that they are trying to hold in one snapshot in time, but as a naturally evolving valley which is protected from too much disturbance and human intervention. It’s a very special place.

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