The Last 4,500,000,000 Years
A Brief Recap
“The old gray rocks so friendly seem,
So durable and brave.”
- William Bliss CarmanIn the New Year I have some posts planned about places I’ve visited, like last week’s post on Inverness. Here are some working titles to posts:
On The Edge
Eloping With A Gibbon
Stone the Crows
Come Friendly Bombs...
Have You Seen Miss Marple?
Dulk Hunts
Paddington Bear and Noel Edmonds
The Dandy Highwayman
Can you guess where any of these relate to?
Before those, let’s briefly recap on the last four and a half billion years…
Somewhere around about four and a half billion years ago, clumps of space debris swirling around the sun began to collide and then coalesce, with the heavier elements binding together to form what would become the core of the planet we call Earth. This great big molten mass began to slowly cool and the outside formed a crust. By somewhere around 3.8 billion years ago there was water on the surface and, soon after, supercontinents which comprised most of the world’s land mass began to form, shift, break up and re-join.
The oldest rock in the British Isles, found in the northwest of Scotland and the Hebrides, was formed about 2.7 billion years ago. It is called Lewisian Gneiss and is what is known as a metamorphic rock. It was formed as a result of the huge temperatures and pressures present deep within the Earth. So, even the very oldest bits of the British Isles have only been in existence for around 60% of the life of our planet. The next oldest rocks, which make up the Highlands of Scotland, were formed from what was the bed of the Iapetus Ocean in the Southern Hemisphere. These are known as sedimentary rocks, literally built up from sediment being laid down for millions of years with the pressure from above turning the lower levels to rock. The third type of rock is igneous, created when molten magma cools.
By six hundred million years ago, the land that I would one day call home was down near the south pole. The far north of England and all of Scotland lay on the continent of Laurentia – which held what is now North America – and the rest of England and Wales formed part of Gondwana – which is where South America, Africa, Asia and Australasia would spring from. England and Scotland were, at that point, about 3000 miles apart. It wasn’t until around 420 million years ago that England, Wales, Ireland and Scotland finally met up. Quite a recent union in planetary terms.
The tectonic plates holding England and Scotland collided and, as the land buckled, the highest mountain range we would ever have – as high as the Himalayas – was thrust up. Although the mountains have been worn down over the intervening aeons, the range still contains our highest peak, Ben Nevis. The lowland hills of Scotland are the crumpled bed of the Iapetus Ocean, created as the plates on which Gondwana and Laurentia sat, were squashed together. The join in the two plates does sit roughly along the modern border.
As air rose over the massive peaks it would have cooled, resulting in clouds and then rain which lashed the peaks and slowly wore them down. The debris which washed away would become Old Red Sandstone and this, in parts of Scotland, can be up to six miles thick. I’m saying that again, six miles thick, that’s the height at which airliners fly. Old Red Sandstone is also found in Devon, the Brecon Beacons and the Black Mountains in Wales, though here it is black rather than red, obviously. The geological era in which it was formed is known as the Devonian – see what they’ve done there?
The parts of the globe that would one day be the British Isles continued to move ever so slowly north and by 360 million years ago the sea levels had risen putting most of Britain beneath the gently lapping waves of a tropical sea. The coral reefs of those seas and the shells of tiny creatures would fall to the seabed and eventually become limestone. The limestone formed in these tropical waters now covers the Mendips, the Lake District, much of the island of Ireland and the dales in Yorkshire and Derbyshire.
As the seas periodically rose and fell, the swampy land gave rise to the formation of coal as plant material became trapped, sank and was compressed. This is known as the Carboniferous period, the sedimentary rock laid down here covers a lot of our landscape, including Edinburgh. That city also has some rather spectacular additions to its geological make-up: igneous rock from volcanic eruptions. As the volcanoes were erupting into a wet landscape, the molten magma must have hit the water and sent great showers of steaming boulders across what would become Scotland’s capital.
By the time that the first dinosaurs appeared in the Triassic period, around two hundred and thirty million years ago, we were part of the giant continent known as Pangaea and had made it as far as the equator. Conditions would have been dry, and arid deserts stretched across all of what would one day be Britain. The hills that lie to the west of Birmingham are essentially fossilised sand dunes from this period in our history.
During the Jurassic, the break-up of Pangaea left us, once again, largely submerged under a warm and shallow sea as we reached roughly the position of the Mediterranean in our journey north. I can’t pretend that I wouldn’t have been pleased for us to stay put at that point but we headed ever northwards. Once again limestone began to form in the balmy seas, this limestone makes up the delightful Lincolnshire Wolds, the Cotswolds and much of Dorset. It also makes up the Tower of London, St Paul’s Cathedral and the front of Buckingham Palace where they stand on the balcony to wave at poor people; because the Portland stone from which they’re built is actually very fine Jurassic limestone.
As the Jurassic seas retreated, dinosaurs could roam the swamps and forests of Britain from Dorset to the Isle of Skye. Dinosaurs of one type or another roamed the earth for around 180 million years. In Britain the dinosaurs disappeared about 100 million years ago as we were once again submerged, though they would still inhabit other parts of the earth until around 65 million years ago. I find it amazing to contemplate the fact that the earliest Tyrannosaurus Rex and first Stegosaurus to walk the earth are separated by roughly the same amount of time as the last Tyrannosaurus and me. There really is nothing permanent about our lives.
As we disappeared again under warm waves, tiny plankton called coccolithophores swam in these seas and would eventually die, their shells sinking to the seabed. Billions and billions of them making up layers which would eventually become that most iconic of British landmarks, the white cliffs of Dover, as well as much of the landscape of southern and eastern Britain. I find it amazing to think that those white cliffs and all the chalk of southern Britain is composed of the bodies of an incalculable number of tiny sea creatures that lived and died in a warm, shallow sea between 135 and 65 million years ago.
Britain began its split from Greenland and North America as the Atlantic Ocean opened up. It was still part of continental Europe, though, and would continue to be part of the continent until very, very recently. As we settled into our current latitude, the ice came. For most of the last two million years, ice has come and gone. Sometimes miles thick and covering almost all of Britain. At their largest extent, the ice sheets stretched from the North Pole to roughly where the M4 motorway sits today. Great, creaking glaciers moving ever so slowly across the land. Gouging and carving scenery like the wide valleys of Wales, Ireland, Scotland and parts of northern England.
South of that, frozen tundra stretched for many miles. Woolly mammoths and woolly rhinoceroses, gigantic bison, two-metre-tall elk and giant deer roamed the icy wastes. Their bones, thousands upon thousands of them, are still hauled from what is now the North Sea by fishermen in their trawlers. The Ice Age was not, in fact, an ice age, it was a series of colder and warmer spells. Almost alongside the bones of the mammoths lie those of lions and hippopotamuses and crocodiles who lived here when the weather was warmer.
There have also been several ice ages during the history of our planet. The first that we have any evidence for is known as the Huronian glaciation and it started about 2.4 billion years ago and lasted for 300 million years; which is quite a cold snap. All of the ice ages - and there have been four major ones since - are made up of glacial periods, when it’s obviously quite cold, and interglacial periods, when it’s rather warmer. We are currently in the Quaternary Ice Age, which has been going on for a little over two and a half million years now. We just happen to be in an interglacial period which we know as the Holocene.
A 1973 report by the British Geological Society put names to the most recent glacial and inter-glacial periods. The chillier periods that these islands have gone through are known as the Anglian, the Wolstonian and the Devensian and the warmer spells, going back in time from the current Holocene period, which covers the last 12,000 years or so, are the Ipswichian, the Hoxnian and the Cromerian.
In next week’s Christmas Eve post, find out a little bit more of the history of mankind in the British Isles and how voles help us to tell the time.
If you’ve enjoyed this post, please consider subscribing and have a look at my book Above the Law about my time flying on police helicopters. Thank you.