280 million years ago molten granite thrust up through the surface of the earth. It was hot. It took a long, long time to cool down and solidify. While that process was happening, the minerals mixed in with the molten granite crystalised causing the granite’s distinctive appearance. That’s what my geologist buddy, John, tells me anyway. Later – a lot later – people came along and realised that granite is a good building material.

Here in Cornwall, people came to extract tin and copper to make bronze. They removed the forests from the granite hills and farmed the exposed land. They used granite boulders to mark out their boundaries, presumably also to keep their livestock in. These dry stone walls were “virgin” territories. Gradually, over a long period of time, plants and animals started to occupy their niches, finding shelter or food there.

This moss (or liverwort) is tucked down into a gap between two boulders. It looks as though something is trying to keep it in the crack by hemming it in but it’s much more likely that the web over it is an opportunistic spider trying to catch whatever insects are coming onto the moss.

How long has it taken for that little moss population to get there? How did the spider work out that putting a web over it would yield food? What happens next? Will a bird spot the spider’s web and eat the spider?

The geological events of the past have given rise to the biodiversity of the present and the future, even though the future is, as yet, unknown. A chance event tomorrow could change this niche and make it suitable for another organism to move in – that bird coming for that spider might poo. It might contain a seed. The seed might germinate. It might grow into a tree. The tree might provide food and shelter for hundreds of tiny species and some bigger species. Opportunity knocks.