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Getting started: 10 things YOU should know about Scotland's geological history

To many people Scotland's history begins a few centuries, or at least only a couple of millennia, ago. However, many things have happened over hundreds of millions of years that have given us the land which today we call Scotland. Selective though it is this top ten will provide a starter insight into Scotland’s pre-human past.

1. We have very old foundations

Rocks dating back over 3 billion years are found in some parts of Scotland. These rocks go by the name of Lewisian Gneiss and were at one time many kilometres deep down in the Earth's crust and then were gradually exposed at the surface. These rocks now form an important part of the landscape of Lewis and Harris and North West Sutherland. Visiting these areas can give one the sense of the immense age of the Earth and its long history.

2. We started off in the Southern Hemisphere

It is possible to identify parts of Scotland, which along with parts of Greenland and North America, existed around 500 million years ago as part of a continent called Laurentia, which existed in the southern hemisphere. For many millions of years this continent moved progressively northwards, crossing the Equator ending up in the Northern Hemisphere.

3. We are comprised of five separate parts

Geologically Scotland is by no means uniform, on a large scale, we can discern five separate and geologically distinct parts: the Lewisian Gneiss and Torridonian of the North West; the Moine rocks of the Central and Northern Highlands west of the Great Glen Fault; the Moine and Dalradian of the Central and Grampian Highlands; the Midland Valley and the Southern Uplands. These areas are separated by big faults or breaks in the Earth’s crust known to geologists as the Moine Thrust in the north-west, the Great Glen Fault, the Highland Boundary Fault and the Southern Upland Fault. Most of these faults can still be identified in landscape.

The period around 410 million years ago was when the original union of Scotland with England took place. This involved the gradual closure of an ocean which separated them with the formation of the Southern Uplands which forms the Border country. With the closing of the ocean, the newly formed Southern Uplands and the other parts of Scotland were gradually shunted together along the fault lines and became ‘welded’ together.

4. At times the landscape was nearly uninhabitable

During its journey across the face of the Earth, the land we now know as Scotland has experienced every climate that we now see on the Earth's surface today, including Arctic cold and extreme desert heat. Volcanic activity would have made conditions very difficult for life at numerous intervals during Scotland’s geological past. Ironically during one period of volcanic activity around 400 million years ago in the Rhynie area of Aberdeenshire, life did have a foothold in the landscape. There silica-rich boiling water from hot springs, preserved some of the most primitive land plants and earliest insects known in the world in a rock type known as the Rhynie Chert.

5. Dinosaurs did live in Scotland

During the ‘age of the dinosaurs’, particularly the Jurassic and Cretaceous periods, Scotland was either hilly ground or submerged beneath shallow tropical seas. There is no doubt that the land areas would have supported a habitat for the animals of the day including dinosaurs. Although very rare, the fossilised bones and trackways of dinosaurs do occur on the Isle of Skye. To date the occurrence of at least 7 species of dinosaur has been proved from the rock record, in what can be regarded as Scotland’s ‘dinosaur island’.

6. We broke away from North America 60 million years ago

For the last 60 million years Scotland, and indeed Europe as a whole, has been drifting away geographically from North America. A line down the Atlantic Ocean is where new rocks are being created all of the time and convection currents in the mantle below, driven by heat from the core, are sending the two continents further apart. This drifting apart with the formation of new rocks is best seen today in Iceland, where the ocean floor has surfaced.

Arran, Mull, Ardnamurchan, Rum, Skye, St Kilda and Rockall represent the remains of volcanoes that formed as the crust between Europe and America split and drifted part with the formation of the Atlantic. Now deeply eroded by water and ice, the internal plumbing of these volcanoes has been laid bare. The Black Cuillin, the Red Cuillin; the Skye and Mull lava fields; the Sgurr of Eigg; and the magnificent columnar lava flow of Staffa, are all famous geological remnants of once great volcanoes.

7. Much of Scotland is at the bottom of the North Sea

Unlike England, where there is great thickness of limestone and chalk rocks, Scotland has only a few pockets of these. However, if we look at the sediments on the floor of the North Sea we can see great thicknesses of similar rock types which were eroded from the Scottish landmass and carried by large river systems and dumped into the deep hollow, which was then the North Sea. These rocks provided the basis of the oil and gas deposits which have now been found in the northern part of the North Sea. The river systems which carried this material gradually shaped a landscape which can still be seen in the eastern part of the country: gentle, rolling plains and plateaux, major river valleys unaffected by later erosion by ice, and wide coastal plains. Some of the best examples of this landscape are the plateau areas of the Eastern Grampians, the major rivers and the coastal plains of Aberdeen, Kincardine and Angus.

8. We were covered by ice at least five times

For the last two-and-a-half million years we have been subject to periodic warming and cooling, with the result that we have been covered by ice many times. We can detect from the deposits which have been left at least five occasions when at least some parts, if not the whole, of Scotland was covered by large icecaps and glaciers. The last of these only disappeared around 10,000 years ago. During this period the old landscapes were gently smoothed, but in some places, as in the high mountains of the Cairngorms and especially in the west and north-west Highlands, existing valleys were made deeper and straighter and the slopes made steeper by the gouging effects of the ice. There is a marked contrast between the jagged and irregular topography of the west compared with the much gentler forms of the east and, put simply, this represents the difference between more active erosion by the ice in the west and more passive action in the east. As a result many valleys and the plains beyond them in the east of Scotland are full of debris, dumped by the ice or by melt waters underneath it or flowing out beyond it.

9. Some parts of the country are rising, others are sinking, and some sliding!

Thousands of feet of ice resulted in Scotland being pressed down into the molten rock beneath its surface. When the ice melted away the land has slowly rebounded, so that beaches which were once at sea level are now tens of metres above that level. The areas which have risen most are those where the ice was at its thickest, particularly centred on Rannoch Moor. Moving out from this point, the amount of rising gradually decreases so that in parts of Shetland (and in the south-east of England) the land is sinking and has been doing so for a few thousand years. It is easy to think that our natural landscape is now stable and has been for many millennia. However, a closer look at many slopes, especially in the Highlands, reveals that a lot have collapsed and many are still on the move. Landslides caused by a variety of factors have occurred, the most spectacular being in the Quirang in northern Skye.

10. Our valleys were filled up

The melting of the glaciers and ice sheets meant that there was a great deal of rock and soil debris which was carried downstream and gradually dumped in the river valleys. In many Scottish valleys you will now see flat or gently sloping benches or steps above the current valley bottom. These represent the levels of the valley bottom in previous times, before rivers had cut through the debris and carried it further seawards. This process is continuing. The debris was often carried out to sea and helped to provide the material to form many of our present sand and shingle beaches and dune systems.

The above is just a taste of a few of the stages in the Earth history of Scotland. The best way of learning more is to go out into the countryside with the SNH Landscape Fashioned by Geology booklets and see it for yourself. Scotland – the Creation of its Natural Landscape, is a good place to start.