The new rock age

Posted by ap507 at Feb 17, 2017 12:25 PM |
Professor Jan Zalasiewicz discusses what extraordinary rocks can tell us about the past

Think: Leicester does not necessarily reflect the views of the University of Leicester - it expresses the independent views and opinions of the academic who has authored the piece. If you do not agree with the opinions expressed, and you are a doctoral student/academic at the University of Leicester, you may write a counter opinion for Think: Leicester and send to ap507@le.ac.uk

One of the extraordinary things about our modern world is just how closely we are brought into contact with rock in everyday life. Now this might seem a little counter-intuitive. As I child, I grew up with cartoons such as The Flintstones and, a little later, sat goggle-eyed through films such as One Million Years BC. There the Stone Age protagonists acted out derring-do amid caves, craggy landscapes and erupting volcanoes or, in the case of Fred Flintstone himself, pedalled a stone-wheeled car past the stone-built condominiums of the neighbourhood. To one of tender years, the evidence was clear: rock was surely a fixture of ancient life, which we modern humans have now largely outgrown.

We might think again. I live amid the low-lying landscapes of the English Midlands – not dissimilar to much of central Europe, or the central plains of North America. Thousands of years ago, these areas would have been densely forested, the forests growing on thick soils that would often have been waterlogged. Where, as a Stone Age inhabitant living so close to so much living nature, would one see rock? Pebbles in the river bed, perhaps, or maybe a tree would be blown over in a storm, and one could scrabble for larger pieces of gravel among the roots. Stone was precious, yes, for those axes and flint arrowheads, but they may have come via long and tortuous trade routes. But rock would not have been a major fixture in this kind of landscape.

But today, now…the forests have been cleared, and the land has been ploughed. I can take a walk out in the countryside, and pick pebbles out of the fields. Usefully, the farmers have even taken the larger blocks of rock, plucked out of the boulder clay – the kind of thing that can damage a tractor tyre or a ploughblade – and stacked them up at the corners of the fields where they can be examined – or even carted off, for the rock garden at home. Had I been a Stone Age human brought in by time machine, this would be a bonanaza.

The time-traveller might be pleased with such a find – but amazed and bewildered at the rock on wider display. Take the houses down the road. Jurassic clay has been scraped from deep in the Earth, shaped, heated to the point of almost melting, oxidized, and arranged into vertical displays, that front habitations. The track leading to each habitation has been lined with a mix of Carboniferous Limestone, shale, and sand grains and pebbles from the Ice Age, all hardened to a tough pale grey surface.

Best not to take the time-traveller down the road (made of chips of ancient plutonic rock mixed with hardened petroleum residues) into town, where it is, pretty much, wall-to-wall rock. And, among those plentiful artificial rocks of brick and concrete, there are slabs of natural rock aplenty, brought in from half-way around the world. And what rock! There is that mainstay of bank fronts, larvikite from Norway, with its beautifully iridescent, centimeter-sized crystals of labradorite. There is grey and purple slate from the Welsh hills, a relic of the mountain building episode that, 400 million years ago, brought Scotland and Anglo-Wales into violent collision. There is Portland freestone, a petrified sea floor from the greenhouse world of dinosaur times, with its cornucopia of fossils.

The modern world is rather like an all-over, wrap-around Aladdin’s Cave of rocks, minerals and fossils, all free to view as one does one’s shopping, strolls home from work, takes the dog for a walk, or even drops in at the bar for a swift half-pint of beer (there are probably some nice minerals on the bar counter, that might catch one’s attention).

And of course these are not just objects, beautiful as they are (they are especially beautiful if one has a hand lens about one’s person, and is not too shy about using it to examine some particular fleck of mineral or rock texture on a wall – this is a matter of geology, after all, and geologists do not embarrass easily). These rocks all have histories, that go back half-way (and sometimes more) to the beginning of our planet: histories of the insides of magma chambers and of volcanic eruptions, of fast currents on the floors of ancient seas and rivers, of the strange life-forms of the past. Some are now globalized histories – that larvikite, for instance, probably now shipped to adorn every city in the world. Some are local, like the blocks of Lincolnshire Limestone in the local clock tower, marking a Jurassic version of the warm seas of the Bahamas. Some are quite specific. Walk round the small, pretty town of Nordlingen in Germany. The local building stones include shattered mineral chips – and tiny diamonds, too, if you had a microscope to hand – the result of an asteroid impact on that landscape 14 million years ago.

There’s high adventure among such things, to be sure. All you have to do is walk around, and look, and puzzle though, the many mysteries on view. Welcome to the new Age of Rock.

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Think: Leicester does not necessarily reflect the views of the University of Leicester - it expresses the independent views and opinions of the academic who has authored the piece. If you do not agree with the opinions expressed, and you are a doctoral student/academic at the University of Leicester, you may write a counter opinion for Think: Leicester and send to ap507@le.ac.uk