The rocks of the north shore of Lake Superior are old, maybe the oldest rocks on earth. They were there before the ice ages filled the lake, before humans, before dinosaurs, before we crawled out of the swamps. Even before trilobites and such. They were spewed out of volcanoes almost a billion ages ago when the earth was creating itself - yes, that's a billion with a "b".
Since then the weather, plants, mosses and lichens are doing their best to grind those rocks into sand. The rocks of Superior were there before us and they will be there after our species passes. I think we are going to be a fast flicker. Maybe the rocks will remember us when we're gone. "Yes, humans, I remember them; they weren't here very long. Let's see, were they here before trilobites? Or after? After, I think."
The lichens themselves are interesting. They are actually a combination of two plants, a fungus and one or more algal species. Not time or room here - and nobody cares much. What I really care about is their tenacious, harsh beauty.