Once upon a geological time on Gigha

I was born 450 million years ago but I looked different way back then. Who am I? You know me! You’ve probably seen me on your trips to the beach in the summer - you might even have draped your towel over me. Yes, I’m that big chunk of rock with the unusual patterns at Port Cùil on the north west coast of Gigha. Here I am in the photograph below.

So, people on Gigha are telling their stories for the ‘Our Island’ project. That’s great news because they have a lot of great stories to tell. I too have an interesting story to tell, so perhaps you might want to hear all about me, after all I’ve been around for a very long time and this is my island too!

Let me set the scene for my appearance. 600 million years ago Earth was very different than you see it today. A giant continent and a single ocean replaced the familiar continents and oceans of today’s world. The atmosphere was toxic and no life on the land existed with only simple organisms to be found in the oceans Yet, this is the time where my story begins.

The single ancient continent of Rodinia was situated in the far southern latitudes of our planet close to where Antarctica is today. But like all continents, both then and now, Rodinia was being rearranged and moved by the energy coming from the planet’s core. The continent split apart creating a new and vast ocean, the Iapetus Ocean.

The ocean floor was piled with mud, sand and lavas and at the ocean’s edge huge rivers deposited more sediment from what was a barren and desolate landscape. Some of this ocean sediment deposited 600 million years ago would eventually become rock. Yes, that’s where I come from, me and of course many of the other rocks that you see on Gigha and Scotland today.

In the geological time scale nothing stays the same for long. Continents continued to jostle and converge and the Iapetus Ocean began to close. The pressure of the continents converging was so intense that the ocean floor sediments were squashed and squeezed as well as being physically and chemically altered by the heat and pressure. This created huge towering mountains, and deep underground new rocks, including little old me, were being formed from the sediments of the long-gone ocean. You can still see the marks on my surface how I was squashed and squeezed all those years ago.

It took millions of years to pass before I saw the light of day, but when water and wind and ice eventually eroded the huge mountains, I was exposed, and for the first time in my existence the Sun shone on my surface. It was a warm Sun, for what you humans now call Gigha was part of a landmass which lay close to the Earth’s equator.

As time went by, the motion of the continents continued and I witnessed changes. Large reptiles which you know as dinosaurs roamed the planet. Plants were growing in profusion everywhere and huge forests covered the the land. This was the age of the creation of coal.

The landmass on which I was situated continued to move north and after millions of years the dinosaurs became extinct and a destructive event took place right here on my doorstep. Around 40 million years ago - a volcano erupted somewhere to the north west between what you call Islay and Mull. This resulted in thin sheets of lava cutting vertically through weaknesses in the older rocks. Once solidified these became known as dykes, Gigha has some great examples. It was sometime after this that your distant ancestors (mammals) became the dominant life form on the planet.

As told by Keith Wilson, a human resident of Gigha. Originally written for the ‘Our Island’ project on Gigha

More information on visiting the area can be found here.