What Lies Beneath?

by Sarah Dobson Author - John Cooper Geology

Our care of the local environment rightly focusses on its thin living surface – the “biosphere” in fact! – where wildlife lives and thrives, and where we humans carve out our lives. But geologists look a little deeper than this, seeking the root causes of what we see expressed on the surface – informed by knowledge of what lies beneath. And for the main part in our own Biosphere area – that means Chalk! We are familiar with the Chalk here firstly through its weathered effect on the landscape – the smooth, strong ‘whale-backed’ rounded contours of our hills and the dry coombes and denes valleys in between. It all seems topsy-turvy to call the ‘ups’ by the term ‘Downs’! Until one remembers that the word ‘Down’ comes from a Saxon word ‘dun’ which translates into ‘hill’. [caption id="attachment_1741" align="alignright" width="276"]Chalk downland at Castle Hill NNR, nr Woodingdean Chalk downland at Castle Hill NNR, nr Woodingdean[/caption]   Perhaps there is nothing more beautiful than a pristine Chalk landscape, such as our Biosphere has aplenty, but with our growing need to cope with a hungry and thirsty population and all it demands we must take care to look after our natural heritage, for as Kipling wrote: “On the Downs, in the Weald, on the Marshes. I heard the Old Gods say: Here come very many people: We must go away. They take our land to delight in, but their delight destroys, They flay the turf from the sheepwalk. They load the Denes with noise.” (‘Very Many People’, Rudyard Kipling 1926)   So what is this Chalk that we owe so much to?  It is perhaps hard to imagine that the Chalk is made of the remains of trillions upon trillions of microscopic marine algae that once lived in a deep sea which covered much of Europe between 98.5 and 65.4 million years ago. This amount of time is mind boggling to us mere humans. The Earth was an amazing place at that time – sea level was up to 300 metres higher than today; it was on average 10 degrees Centigrade warmer than today with sea water temperatures at the surface some 20-30 degrees higher. There were no ice caps. Exceptional conditions compared to now, but perfect then for the blooming of marine algae called coccoliths, minute flora whose remains after their short lives rained down on to the sea floor for perhaps 40 million years! The limy shells of such small organisms created a chalky mud on the sea floor at the rate of only 25mm in each thousand years but because it happened for 40 million years this adds up to a kilometre of chalky mud! And in the time since this hardened to form our familiar Chalk. You can also see horizontal layers in the Chalk, together with layers of flint nodules, the story of which will have to wait for now! The period of time in which this happened is known as the Cretaceous (latin Creta- means Chalk). Since its formation the Chalk and all the layers of rock that make up the British Isles have been lifted up by the huge planetary forces which created the Alps and the north Atlantic Ocean, and weathered into our present landscape by rain and ice. In those warm Cretaceous days all those millions of years ago, marine algae were not the only form of life living in the clear seas. Sea urchins, fish, starfish, shellfish, sharks and marine reptiles have all been found as fossils. Whilst it’s not always easy to find them these days, a visit to the Booth Museum of Natural History on Dyke Road in Brighton is a must to see the displays of splendid Chalk fossils collected in the past. [caption id="attachment_1744" align="aligncenter" width="573"]Fossil Fish in Chalk from Upper Cretaceous period (Booth Museum) Fossil Fish in Chalk from Upper Cretaceous period (Booth Museum)[/caption] A5 Fossil Fest flyer front-001You can find out more also by going to the Lewes Fossil Festival on the weekend of 24-25th September 2016, where there will be lots of free family fun activities themed on dinosaurs and inspired by the local Victorian natural scientist Gideon Mantell. And for all things local and geological, take a look at the excellent work of the Sussex Geodiversity Partnership.   To see our Chalk at its best, visit the natural cliffs eastwards beyond Saltdean and on to Newhaven, but watch out for the tides! The Chalk cliffs can also be seen safely all along the Undercliff Walk from Brighton Marina eastwards to Saltdean. Inland the Chalk quarries near Lewes, especially those near Malling Down, provide views of Chalk rock also. [caption id="attachment_1742" align="aligncenter" width="453"]Undercliff walk east of Brighton Marina to Saltdean Undercliff walk east of Brighton Marina to Saltdean[/caption] John Cooper Keeper Emeritus, Booth Museum of Natural History, Brighton john.cooper@brighton-hove.gov.uk
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