Deep Past 1. Hell to High Water




On the seventh day, God rested. He put his feet up, had a beer and took his eye of the ball. Chaos ensued. 

Geology is the study of pressure and time. That's all it takes really, pressure and time. (Red: The Shawshank Redemption) 

Nothing of early Earth that can readily be seen in South East but I thought that I ought to acknowledge the canvas before asking you to admire the painting. There are two big things that you need to be aware of. Everything else is detail:

As I am sure you know, it all started with the Big Bang some 14bn years ago which, initially at least, wasn't big and wasn't a bang. If you want an explanation try this short video: Link : Big Bang .  In any event, it wasn't until 4bn years later that the game kicked-off on Proto Earth.

This would have been a hellish time to visit. Early Earth lacked a magnetic shield to protect it from the nasties that the sun was spewing out and l and any atmosphere to shield it from meteorites. It rotated every five hours or so and the moon was much closer, triggering tsunamis of molten lava sloshing across the surface.  Take a look at it moon now and see the craters. Ouch. 

The 'Hadean' period on Earth. Don't go there. 

Then, slowly, it started to cool. A crust formed on the surface, which fractured into giant slabs or 'tectonic plates' over time. These started to shift and slide around on the more viscous deeper layers, as is propelled by Gods playing dodgems. With attitude. When plates clash, they bury and got buried by each other. The Earth is restless and an enthusiastic recycler. We still don't really understand the dynamics and nothing can be seen locally that is the legacy of all this, but our continents and oceans ride on these plates and have changed a lot and travelled a long way to get to where they are today. 

The Early Continents

The diagram below illustrates how complicated it all is. Credit to the Encyclopaedia Britannica Kid's Edition, which is about my level. I know that you can't readily make out the detail on a phone so if you are interested you can find the original it using this link: Tectonic Chaos

Or if you would rather have another video, see Link: Tectonic Plate Dodgems

As the continents on their plates drifted around and collided, they created oceans and troughs, mountain ranges, earthquakes and volcanoes. Those oceans and mountain ranges came and went. When land sank below the surface, thick layers of sediments gathered on top of it, only to be eroded away when it rose to the surface again. Nothing stayed put. Nothing stayed the same.

The result was that yesterday's ocean floor might well have ended up on a hillside miles from the sea and today's mountains will one day be sea bed. Our own area has bobbed up and down like a yoyo. It still does, just very, very slowly; and at present it is sinking at about 1mm a year relative to sea levels which, as you know, are rising for other reasons.  Don't throw your wellies out. 

It didn't help that changes in the chemistry of the atmosphere periodically switched the planet from being a freezer to a greenhouse. Early 'global warming' might have been down to huge volcanoes vomiting carbon dioxide on a scale which produced an early atmosphere, which was unbreathable if protective. Oxygen appeared later, probably minted by bacteria in the oceans and subsequent changes in the mix of gases further exacerbated the rise and fall of the sea levels. A lot. This all had a profound and generally negative effect on the career plans of early lifeforms. Few survived their redundancy notices. 

The key to making sense of what all this means, is to factor in the timescales involved. With our perceptions constrained by our senses and eye-blink life spans, these are unimaginable. So I will now ask you to try and imagine them. 

At the moment your current perch is moving away from America at about the speed at which your nails grow. That might not sound much but over, say, ten million years, which is just an eyeblink in geological time it would be 200 km away. The vertical hold shifts as well. The Himalayas are currently rising by around 1 cm a year because the tectonic plate carrying India is bashing into Asia. The highest point in S.E. England at 300m is Walbury Hill in Berkshire.  At that rate you could add something that height in just 30,000 years. I have known slower building lifts! 

In short, with this number of violently interacting forces at play, and with plenty of time for it, there is no chance that an underpowered dilettante like me could cram 4bn+ years of history into a short, linear and comprensible blog post. Sorry, but since no shadow of it falls on most of the natural landscape in this area anyway, there is nothing to be gained by squinting too hard through the geological time-telescope.  

If you want to see really early stuff without travelling afar, you have to travel, to North West Scotland perhaps. Or better still, try Link :  My Geological Pub Crawl    

That sounds very dry even as I write it. It is, after all, paleogeology. Maybe I could make it all sound more like a ghastly swingers party in the second circle of Dante's Inferno? Sex it up with some 'saucy postcard' style innuendos about bumping and grinding, eruptions and maybe even subduction? Then again, maybe not. 
 
The curtain closes on this first Act in our tale, some half a billion years ago. Much of the surface of the planet is submerged beneath vast oceans and land was concentrated in the Southern Hemisphere and, finally, beginning to develop some of the soil cover that would support plant growth  The bits that would one day do a 'reverse Atlantis' and rise above the waves to become South East England, were part of an ancient sub-continent rather beautifully named 'Avalonia', tacked onto a bigger land mass called Gondwana and floating about down near the South Pole. 

Earth, 450m BC 

The atmosphere was at last relatively breathable and Earth had also gained a magnetic field which protected it from the Sun's most beastly rays. Life was springing to life. Initially it was just microbial speed dating. Later, the seas were filled, initially mostly with very small and simple creatures pootling (!) around amid some weird and wonderful fauna and flora. By the end of the period, a myriad of bizarre creatures were emerging from nature's skunk works. I love David Mountain's description of them as 'Pokemon designed by H P Lovecraft'. 

The end of this First Act in the show was a mass extinction. There will be several of these and it appears that this one was down to global warming. Listen up!  Most living creatures copped it. If they hadn't, you might now look more like one of the monsters from Dr Who. 

At the very end of this early period, Avalonia crashed into another early continent, Laurasia. Scotland was piggy backing on the latter. The result was the joining of what became England and Scotland, along a line between what is now the Solway Firth and Berwick. Today's border follows that line and everything you were taught at school about the two countries being joined in the Act of Union in 1707, is pure misinformation. 

The Anglo-Scottish Border now

What is left of Avalonia now lies deep in our regional basement, hundreds of metres below the surface and later sediments. Hurrah! Even though our bit of the planet was underwater at this point in time, it won't be too long before I can get to something you can sit and picnic on. Or even brush your teeth with. So in my next post, I will cover what happened next, after things settled down a bit. 

The sad fact is that, while the wonderful Nordic stories about a world of ice and fire are spot on, the rest of the stuff about immense Ash trees, ice giants and enormous cows, isn't actually attested by science. More's the pity. If this disappointment is too much to bear, take a look at this really good interactive graphic showing the changes through time. 

The upside of all this is that Britain's strange path, wandering around the planet, submerging and emerging and often ending up on the liminal edges of early continents, has left us with richly varied geology and some wonderful and unique landscapes. The chalk lands of the South East are among them. 




Fast forward a few hundred million years. To labour the point, the goings-on before then, don't influence our local modern landscape very much. It is relatively youthful in geological terms and spent a lot of the time underwater. But now we can start to talk about stuff that you can see hereabouts. 

As we get into a bit more detail, please don't forget that  I am a not a paleo-anything but rather a recreational scribbler indulging in an heroic degree of generalisation in a quest for simplicity. 

The header pic is a map of the world in the Jurassic period, named after the film.  If they ever make a documentary about the Age of Dinosaurs, the opening and closing credits can be set against two massive extinction events which, like their forerunners, comprehensively shuffled the cards in life's game of chance, but never quite terminated it. The first and greatest was at the start, perhaps 250m years ago. Maybe 95% of life on Earth disappeared. The cause was global warming, again, caused by an increase in carbon dioxide resulting from volcanic activity i.e. it wasn't  us, we have an alibi and were simply not around to try the DIY version. 

In the background, land masses continued to shuffle about. New lifeforms appeared, both in and out of the water. The Earth still had two great continents, Gondwana, which I have already mentioned, and Laurasia. They were separated by the beautifully named Tethys Sea. Wouldn't it be great to get the job of naming this stuff? In Greek mythology, Tethys was a Titan, the wife of Oceanus and the Goddess of Fresh Water. 

Tethys

As you can see from this contemporary picture, she had wings growing out of her head. Frankly, judging by the fashions of that period, that probably wouldn't have been thought weird. For instance, take a look at way that the Triassic reptile below carries his golf clubs. Evolution plays strange tricks.

Longisquama


About 200m years ago, probably on a wet Monday in March, as the world continued its recovery, what was left of that Carbon Dioxide ensured that the climate was warm and the polar ice disappeared. Sea levels rose and again covered a lot more of the planet as you can see from the map at the head of the post. The first birds had taken to the air and a few small and rather odd mammals appeared. You might even see some plants that would look familiar to gardeners today; the ancestors of ferns, conifers, ginkgoes and Yuccas. This was the Jurassic Period and there was no grass. None. An odd thought. 

Dinosaurs turned up later and were indeed big beasts; Titanosaurs, Megalosaurus' and Iguanodons. But T Rex and his pals, as portrayed in the Jurassic Park film, actually only emerged on the scene in the 'Cretaceous' Period which came nextIn fact, more time passed between the first dinosaurs and T Rex, than between T Rex and you. Hollywood lied to you; nothing new in that, but did you know that their deceits didn't stop there. The dinosaur sounds were just amplifications of the noises that Tortoises make during sex. 

T Rex. Circa 1970. Sorry. Couldn't resist it. 

By this time our bit of the Earth's crust had wobbled northwards and was perched around the latitude of modern Morocco, part of the islands and shallow seas in the 'Eurasia' bit in the upper middle of the map of the globe at the top of the post. The Jurassic Coast Visitor Information Centre in Dorset had yet to open.

Those shallow seas would have teamed with life. As well as Monsters Of The Deep, there were vast, vast forests of glass sponges and countless corals and tiny creatures, many comprising only a single cell which, on dying, sank to the seabed. And of course the oceans and lakes were also full of the usual sea muck, sand, gravel and the river-borne debris of the ever-eroding continents.

Nemo wouldn't have stood a chance! 

The Cretaceous period was fiery, hot and wet. The three are related. Fiery, because there was massive volcanic eruptions as the ancient southern continent of Gondwana split up. That increased the mount of atmospheric carbon dioxide which as you know leads global warming. That in turn led to melting ice caps and rising sea levels. If you visit, take some oxygen and very, very good insect repellent. 

This brings me to the point of this post, namely the creation of the rocks that that the countryside of South East England sits on. Britain as a while is a geologist's paradise, with great variety having drifted around the world and formed from the flotsam of broken continents. Our bit in particular spent a lot of time under the sea where aquatic ooze, compressed under its own immense weight and the ocean above it, morphed into the rocks that lie deep under London today but which come to surface in the hills around it. 

There are four main types; limestone, sandstone, chalk and various mudstones. Each was laid down as ocean floor at different times and in different places from different mixtures of the ooze. Hereabouts, the Limestone  of the Cotswolds is mostly Jurassic while the chalk of the Chilterns and Downs was laid down in the Cretaceous (i.e. chalk) period which came next.   

You might wonder how there was ever enough compressed ooze to create hills. The answer, once again, lies in the unimaginably long timescales involved. It might take a decade to create a layer the thickness of a slice of ham. Left uncompacted, this would give you a pile the size of Mt Everest over ten million years. That is only a passing moment in geological terms, but it is easily long enough to create a thick layer of  'sedimentary' rock even after compaction and erosion have done their business. 

Antarctica in the mid Cretaceous period

I want to talk a bit more about these rocks because they have an immense influence on our landscape But I also don't want blog posts created to be read on phones, to get too long. So they will get a post of their own; the next in the series. What follows are what one of my sources describes as ‘penecontemporaneous palaeogeographic’ events. Save that one for your next scrabble game!  

By the end of the Cretaceous period, temperatures and sea levels were falling again and the sea bed and the sediments heaped on it were uncovered. It was still being mangled by the slow but never ending and violent movements in the Earth's crust but the flotsam and jetsam of broken continents, floating around northern seas, were morphing into something recognisable as Britain. At the same time, the exposed land started to be viciously shredded by rivers and eroded by wind, rain and chemical solution. Much of that eroded material became various types of clay and mud and, since this process has been going on forever, some clay pre-dates the rocks we find, and some was formed later.  

The coda to the Cretaceous was yet another great extinction. This one is usually ascribed to an asteroid the size of Luton crashing down in what is now Mexico, shattering the Earth's crust, creating huge tsunamis and blanketing the planet with soot and dust. Years of darkness and ensued and acidic rain poisoned what wasn't killed by the loss of sunlight. The result was that 75% of all of the species of life on Earth vanished, notably the dinosaurs and ammonites. 

Oh no! It's Luton. 

If you are actually interested in this stuff, I have two suggestions for books to read. Neither are difficult or technical. Both are colourfully written. Sadly neither author remembered to take a camera into their time machine. 

'Otherworlds' by Thomas Halliday, which describes what you would have seen and found if you could do a bit of time travelling back through the epochs. 

'Vanished Ocean' by Dorrik Stow is about the birth and dwindling away of what was once one of the greatest Oceans on Earth, the Tethys Sea. 

There are also two great podcast series. 



And you can find another really nice graphic animation showing how the continents (and London in particular if you want) moved & morphed over time at: 
 

The Next Post in the Series : Link  Coming Up For Air




 

Comments

Popular posts from this blog

Start Here : Explanations

Mapping Apps Review

The Suburban Semi