Thursday, 14 November 2013

The ancient rocks of Leek

I was showing my daughter the prominent bands of Sandstone rock that lies at the bottom of Broad Street and on the road to Cheddleton. They are noticeable by pebbles stuck in the rock like currants in a cake. The quartzite pebbles are very smooth and suggest that they were once part of a fast flowing river system. It must have been a formidable obstacle to the 19th century road builders blasting their way through the town.

I was right. The Sandstone dates from the Triassic period of around 250 million years ago at a time when life on Earth nearly came to an end. Other rocks around Leek are older; the grit stones of the Roaches are from the Carboniferous period of 380 million and the limestone of the White Peak marking the one time existence of tropical coral sea date from 340 million years.

I have always been interested in the age of the Earth, which irrespective of what Creationists might think, is about 4 billion years old. Recently, I bought a book on a history of the Earth and I looked up the early Triassic period and how the area might have looked.

During this period there was only one Continent called Pangea. Britain lay near to the ocean that circled Pangea called Tethys and was closer to the equator. The Leek deposit is part of a larger group called Sherwood Sandstone covering areas out to Cheshire and eastwards towards Nottinghamshire.

 Weather conditions during the early Triassic were monsoon- like in this time which accounts for the pebbles worked smooth by the deluge and indicate a delta type area similar to the Nile today. Temperatures were high and a desert climate existed.  It was a forbidding landscape with little life. Few fossils exist in the local rocks. Later in this epoch however the first dinosaur made their impression on the landscape.

 Chirotherium, a crocodile-like ancestor of the dinosaurs, left five fingered hand-prints behind in the sand which were found millions of years later by fossil hunters. A fine example can be seen in the World Museum in Liverpool found in a sandstone quarry on the Wirral.

The Triassic period saw a long process of re-birth after the calamitous previous era- the Permian- when the planet saw a Mass Extinction event with increasing volcanic activity, methane release and acidification of the seas resulting in raised temperatures and the extinction of around 90% of all species on the Earth. It was called the Great Dying. It took the planet millions of years to recover and the rocks in the south of the town bear witness to a period when the Earth was recovering from this cataclysm. It was the greatest Mass Extinction event of which there have been five. Scientists think that the current global warming might result in the sixth Mass Extinction event now.