In my reminiscence box, in the drawer marked 1960s, I am going to add a piece of rock. Maybe a piece of coal, maybe a piece of green serpentine, maybe a piece of Old Red Sandstone. This will be to remind me that it is during my lifetime that something tremendous was discovered, something that changed the way we all think about our planet, as totally as Darwin’s theory of evolution by natural selection changed our view of ourselves. And I don’t mean the invention of computers.

When I was in the sixth form, I was studying for an A-level in Geography and an O-level in Geology and I had to learn about Wegener’s Theory of Continental Drift. The idea that the continents changed shape over time, and that the pieces moved into different positions all over the planet, was not a new one. Many people had suggested it over several hundred years. Alfred Wegener had published the most systematic version in 1912. However, it was not until the sixties that the fully-fledged theory of plate tectonics was developed, with an explanation of the mechanism by which the continents might behave like this. We now have maps showing the configurations of the landmasses at most periods in earth’s history.

This is why what is now  Scotland was once situated at the equator, home to rain forests that formed today’s coal, and why the beaches of Orkney are covered with bright red pebbles and St Magnus Cathedral in Kirkwall is built of red and yellow sandstone.  The bedrock over most of Orkney is Old Red Sandstone (well, not all of it is red), formed between around 420 to 360 million years ago, during the Devonian period, when the climate where Orkney then lay, 10 degrees south of the equator, was hot and dry with heavy seasonal rains.

Between 480 and 420 million years ago, during the Ordovician period, two continents moving across the surface of the Earth collided and part of the ocean floor was pushed to the surface. The piece of green serpentine I picked up on the island of Unst in Shetland was part of that ocean floor.

Today this is as much part of everyday knowledge as the reason for day and night, or the seasons, or why some people have blue eyes and some brown. It is as great a revolution as the invention of computers. I recently watched a TV programme in which David Attenborough talked about having the same experience – it was a new thing when he was going through university, too. My generation have seen a lot of new things.