Lichen takes a long time to grow on stone, but it takes even longer for anything to grow on concrete.
I took this photo yesterday morning while walking the dogs.
Indoor-outdoor carpet glued in place on a stoop to keep visitors from slipping and maybe give the porch some 'green appeal' had presumably got too weathered and most of the stuff had been scraped off the steps leaving patches of green that looked for all the world now like manmade moss.
Voila! Time has been sped up.
By contrast the time it takes for real lichen or moss to grow on a rock is measured in ages. Rocks of course have all the time in the world, but do we?
All this musing reminded me of a clever animation that is probably worth posting again here.
Click the link below to see it