100 million garden projects

We drove over a saddle and looked down on the valley. A hundred and twenty years ago it was thick forest and swamps. Now it is rolling farmland, with wind-breaks and fences and drains and irrigation and flood control and roads and towns. Have you ever built a landscape feature in the garden: a wall, a terrace, a path? How much effort did that take? Now look at the place you live in. With your little project as one unit of effort, how many units can you see?

The population of the valley is say 100,000 people. A hundred years ago it was 10,000. So say 50,000 people per year over 100 years. Assume 50% of them productive (that was then - hardworking farm folk: modern society struggles to get 25-30%). That's 2,500,000 person years of work. At 300 days a year (that was then...) that's about 100 million garden projects. By a small population in a small valley over just one century.