Blueprint

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Inishtrahull, County Donegal

 
          inishtrahull

Time Period

Ireland's Birth

1780 Million Years Ago

 

They are to be found off the coast of County Donegal and mark a moment in time 1780 million years ago when the very first piece of what we now call Ireland was formed.

Here, at Innistrahull Island, are the oldest rocks in Ireland whose twisted, fractured and weathered appearance trumpets their vast age.

Subjected to a range of geological pressures and processes over their long life, the rocks themselves have morphed and fractured from when they first formed during what is termed the pre-Cambrian period of Earth’s history.

Experts have used the latest dating techniques to examine the mineral composition of these rocks to determine their origin within this period.

The colourful bands visible on the rocks themselves represent the various minerals which have separated out over time due to the geological pressures acting on them.

This type of metamorphic rock is known as Gneiss (pronounced: nice)

However, the real story behind these ancient rocks is not only their age and physical appearance, but the fact that they are totally unlike any other rocks in Ireland.

So where did they come from?

Geologists have only recently been able to uncover the mystery behind the rocks at Innishtrahull, and it seems the main actor here, as it is throughout the geological story of Blueprint, is plate tectonics.

They discovered the rocks are almost identical in their make-up to those found in Greenland and, to a lesser extent, the Scottish Hebrides.

And the reason for this is that they were all once part of Greenland – or at least the large continental land mass which Greenland was part of nearly two billion years ago.

But it was the movement of tectonic plates over millions of years which caused the small rocky outcrop that would become Innishtrahull to break away from Greenland and drift over time to its current position off the coast of Malin head.

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