In old neighborhoods in the US (anything over a century is old in the US) you find the craziest things in the soil. The sheer amount of glass and plastic and metal is staggering. Just digging the holes for ornamental plants was enough to make me realize all food gardening would need to be in raised beds with liners and known soil.

In parts of the world with longer periods of habitation (all of them) what do you find in the soil?