I'm not sure how old it is, maybe somewhere in the 20-year range, but it is almost completely covered in various mosses, lichens, fungi and liverworts. A great many different things are growing on it:
I particularly like the miniature moss-ball. Some mosses, like the blue one at the top, grow by spreading sideways, others by growing from a fixed centre. Yet others, like the one on the bottom, seem to head off for parts unknown like tiny explorers.
Looking even closer, I am amazed at some of the wonderful patterns that appear:
Too bad I don't have my microscope with me!