What lies below

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By Catherine McGuire, Hampshire & Isle of Wight Wildlife Trust

Every aspect of life in Hampshire today is underpinned by the rocks beneath our feet. The Trust’s Ecology team did a spot of time-travel to showcase the wonders of Hampshire’s diverse geology – its geodiversity.

Geodiversity is the variety of rocks, minerals, fossils, landforms and the processes that have created these features throughout geological time.  Understanding geodiversity allows us to look back and picture a time when Hampshire was a very different place indeed.

For example, stand at the top of Portsdown Hill and close your eyes: with a bit of creative thinking, you’ll be standing on the bed of a warm, shallow, tropical sea, around 85 million years ago. It’s teeming with life. Sea urchins creep across the seabed, ammonites propel themselves through the water, huge marine predators glide stealthily past you. The water isn’t entirely clear; drifting like snow around you is a constant rain of billions of microscopic calcium skeletons from these plankton-rich waters.

Fast-forward to the present and you realise you’re atop the world’s largest mass grave. It took the accumulation of countless planktonic skeletons over millions of years to make the hill on which you now stand. And about 500 miles to the south and a few million years later, the immense forces that forced up the Alps in Europe also sent ripples north to push up the chalk in Hampshire and form the rumpled landscapes that we call the North and South Downs.

So, how have these processes influenced what lives now? Today, the thin, nutrient-poor, chalky soils on Portsdown Hill support flower-rich communities scattered with bee and fly orchids, thyme and marjoram. So characteristic of chalk downland, they in turn support a diverse range of insects, particularly butterflies and moths. The steep chalk cliff at Paulsgrove has even hosted nesting peregrines.

Over millions of years, the global ebb and flow of the seas and movements of the continents wrought remarkable changes to the appearance of what became Hampshire. The drift of vast rivers, lagoons, and shallow seas at various times through the geological past deposited a variety of clays, sands and gravels about the county. Visitors to Swanwick Lakes may not know that it was once a dramatic open landscape of estuarine muds and saltmarsh supporting an array of wildlife.

The story in the rocks is a fascinating journey through time that shows Hampshire transforming from an ancient tropical sea to its present species-rich grasslands, vibrant rivers and ancient woodlands. So, next time you take a walk, remember there’s more to that familiar landscape than meets the eye.

You can explore Hampshire’s past through a fascinating section on the Trust’s website. Guides (available to download) to a selection of family-friendly sites in Hampshire promise to transform a simple walk in the county into a remarkable time-travelling event. Visit www.hiwwt.org.uk  and click ‘Get Involved’.