Updated: Sep 30, 2020
Today Ireland is a small island at the north-western edge of Europe. Its origins however lie far away from its current position, on the other side of the globe somewhere between the equator and the south pole. The story begins some 400 Million years ago when the two parts of which Ireland is made of came together.
At the time what would become Ireland’s north-west belonged to the continent of Laurentia, as did Scotland, Norway and the eastern seaboard of Canada. The south-east of Ireland was part of Avalonia, together with England, Wales and northern France. The two continents were separated by a wide ocean, the Iapetus, but over millennia the landmasses of Laurentia and Avalonia moved ever closer together until eventually they collided, forming the supercontinent Pangea and merging the two halves of Ireland in the process. The line along which the two continental plates crashed is still evident today in the mountain ranges of the northern half of Ireland like the Sperrin Mountains and Ox Mountains that display long axes that trend north-east to south-west. These mountains are part of the ancient Caledonides that once stretched from Scandinavia, through Scotland and Ireland to Newfoundland and Appalachia.
Pangea then started its slow journey from the southern hemisphere to the equator where it arrived some 340 Million years ago. It is here where the foundations of today’s Ireland were put down. The part of Pangea that would later become western Europe disappeared under a warm and shallow sea, only some mountain ranges, the peaks of Wicklow and Donegal among them, were left as islands. This tropical sea was populated by corrals and crustaceans. Over the following millennia the remains of these animals would be transformed into limestone that today forms almost half of Ireland’s bedrock. In areas where the limestone is exposed, like the Burren in County Clare, countless fossilized remains can be found from sea level to mountaintop, giving us a glimpse back in time.
The limestone hills of the Burren
At Pangea’s coast mighty rivers brought sand and silt and dumped it into the ocean where it was turned into sandstone and shale that today is visible at many places along Ireland’s western seaboard like Downpatrick Head, the Cliffs of Moher and the Loop Head Peninsula. Around 300 million years ago the continuous plate movements under Pangea formed a massive mountain range, the Hercynite Mountains. The remains of those mountains that once stood taller than the Himalayas live on in the MacGillycuddy’s Reeks and the Caha Mountains in the south of Ireland. The beginning of the end for Pangea came 200 Million years ago when the plates that made up the super-continent started to move away from each other. Ireland had almost reached its current position when the super-continent slowly started to break apart into Laurasia in the northern hemisphere and Gondwanaland south of the equator. Around 55 Million years ago a series of volcanic eruptions split Laurasia and the European and American continent started to form while the Atlantic Ocean opened up in between. During this time huge fissures in the earth’s crust also opened up in the north-east of Ireland, allowing floods of molten basalt to cover the landscape again and again for some 2 million years. The basalt columns of the Giant’s Causeway, the volcanic plug of Slemish and the Antrim Plateau are the remains of this violent period.
The final big chapter in Ireland’s early history are the ice ages. This period started some 17 million years ago when a drop in earth temperature triggered the formation of the polar ice caps. Over the following millennia the northern hemisphere endured cycles of warming and cooling during which the ice of the arctic extended and retracted, covering northern Europe including Ireland periodically in thick ice sheets. It was this coming and going of the glaciers that shaped much of Ireland’s landscape. Especially the two latest glaciations, known as Munsterian (300.000 – 150.000 years ago) and Midlandian (80.000 – 10.000 years ago), have been responsible for some of Ireland’s most remarkable landscapes including the peninsulas of the south-west coast, the Burren and the islands of Clew Bay.
The last glaciation ended some 10.000 years ago. This doesn’t mean however that Ireland had been a frozen and empty wasteland before that. Short lived warm periods during the glaciations allowed plants and animals repeatedly to establish themselves. Bones of the spotted hyena for example support the theory that between 45.000 and 20.000 years ago Ireland, or at least parts of it, had a tundra like character. The spotted hyena most likely shared Ireland with the mammoth, wolf, brown bear, reindeer and the mighty Megaloceros Giganteus, also known as Irish elk. When temperatures started to drop once again 25.000 years ago and glaciers started to advance south, the flora and fauna retreated back to the continent. This last cold snap only lasted around 10.000 years and as soon as the glaciers started to disappear plants and animals returned to Ireland. It is thought that reindeer and Irish elk were among the first to return, followed by wolf and brown bear and eventually by species that still live in Ireland today like the red deer and hare. Some theories even suggest that some species managed to survive the latest glaciation in some far flung corners of the south-west or some lonely mountain tops that escaped the ice domes.
The arrival or survival of plants and animals during and after the last cold snap is still a bit of a mystery and ongoing topic of discussion. As soon as the glaciers started to melt sea levels rose considerably but it is now widely accepted that land bridges between Scotland and County Donegal as well as Wales and County Wicklow existed for long enough to allow plants and animals to cross over into Ireland. A look at the seafloor map makes this indeed likely. The Irish Sea reaches depths of up to 100 meter but is considerably shallower in the north between the Scottish island of Islay and Malin Head on the Inishowen peninsula. Further south an underwater ridge runs east to west between Wales and Ireland’s east coast. Other factors could also have played a role in the formation of land bridges. The land itself, now being free from the weight of the ice, bounced back, an event that is still visible today in the raised beaches on Malin Head. This rebound of the earth’s crust could have offset the sea level rise for a considerable amount of time. Moraines, a mix of rocks and sediment left behind by the glaciers, could also have formed short lived land bridges between Ireland and its larger neighbour. In all those scenarios time plays a crucial role. While animals could have easily used these land bridges to move into Ireland within a rather short time frame, plants tend to advance at a much slower pace. Despite some scepticism and the rise of other theories, like seeds of trees and other plants arriving by sea, the most likely scenario is that of an orderly migration via the land bridges. This means that animals wandered with their slowly extending habitats, first tundra and later forest, from Scotland and Wales into Ireland. This of course doesn’t rule out the later arrival of some species over the Irish Sea or the English Channel. It is also likely that the first human immigrants brought, knowingly or unknowingly, plants and animals with them.
With the glaciers gone and continuously rising temperatures the Irish landscape underwent considerable changes. Some 13.000 years ago the Tundra was already well established, and the initially rather barren plains were soon transformed into fertile grasslands. One of the first flowers to bloom here was most likely meadowsweet, a plant that is still common in Ireland today. Juniper was the first shrub that settled in the Tundra, followed by birch and hazel and together they formed the base for Ireland’s forests. The first pines appeared around 9500 years ago followed by oak and elm which quickly spread all over the island.
Shadow of the past: Oak forest at Old Head, County Mayo
These first people found an Ireland very different from what we know today. The whole of the island was covered in vast forests that were dominated by oak and pine. Initially the first settlers lived as hunter gatherers mainly along the coast and had little impact on their new home. This however changed when the hunter gatherers became farmers and settled down. The now settled stone age people not only built lasting monuments like the Pounabrone Portal Tomb (5800 years ago) and Newgrange (5200 years ago) but they also started to clear the forest for building material and to make space for growing their crops.
The final big change happened around 3000 years ago. By then men was well established in Ireland and had already made considerable changes to the landscape and had turned parts of the native forest into farmland. Then, over a rather short period of time, the climate changed from a continental regime with warm and dry summers and cold winters to the Atlantic climate Ireland is infamous for today. It became wetter and generally milder, conditions that triggered the formation of the bogs. Until then raised as well as blanket bogs only existed in only a few suitable corners of the landscape. Looking at the bogs today it becomes clear that this change must have happened rapidly. In some places it seems that the forest has been swallowed whole by the advancing bog and perfectly preserved tree trunks embedded in peat are a common sight. This climate change not only took the forest by surprise, it also interrupted the human way of life. Proof for this are the Ceide Fields in Co. Mayo, an ancient field system covered by several meters of blanket bog that was discovered by pure chance. It is thought that this stretch of coast was once arable land and so supported a big farming community. The complete removal of tree cover however, together with the increased precipitation that came with the change in climate, turned the fertile soil into barren land. A tree’s canopy keeps much of the rain away from the ground and the water is either being absorbed or evaporates back into the atmosphere. Once the canopy is gone all precipitation enters the ground and over time washes out the nutrients from the soil. The particular topography of the Ceide Fields on a coastal hillside probably sped up this process. The settlers had to leave their home in search for new land and the fields were left to the fast-growing blanket bog.
Cutover blanket bog, County Clare
Ireland’s new climate regime, the formation of the bogs and continued clear cutting of forests to make room for more agriculture and people eventually transformed the country into the land of fields, hedgerows and stonewalls we see today. Ireland’s claim to be wild and unspoiled is therefor rather far-fetched. Most of Ireland’s landscape is in one way or another men made. What however happened in Ireland was an amalgamation of men-made and natural landscapes and for a long time there was a deep connection between the people who worked the land and the natural world. Hedgerows took on the role of the forests and certain shrubs, especially blackthorn and hawthorn were considered untouchable. The Burren, a landscape that would never have come into existence without human interference, is today a refuge for many plant and animal species.
Over the last century this respect for the landscape has unfortunately mostly disappeared. Large scale farming, tourism, industry and general consumerism and ignorance have left a mark and created an Ireland that faces widespread habitat destruction and the disappearance of iconic animals like the corncrake and curlew, polluted lakes, rivers and coastal waters and climate change induced sea level rise and an increase in storm activity.
Carsten Krieger, Summer 2020