Top layer eventually turns to dirt over time

I like that you can't plant on rock but it is a logistic pain to dig up 1 layer of rock and then backfill with dirt. Dirt is also the best background to see your factory, another factor in laying 1 layer of dirt down.
I appreciate that it adds some depth to managing the terraforming but it can also be tedious and time consuming. I would like to suggest and option to have the top layer of rock/slag turn into dirt over a very lengthy (50+years) amount of time much like compost/waste turn into dirt. This would allow us to terraform with out micromanaging a dirt layer and we would eventually have that usable and easy to see dirt covering the areas we terraform. Leaving it as an option in the difficulty settings would allow people who truly enjoy the terraforming aspect of the game.

The other option for this would be to allow building of farms on top of non dirt surface, but then require delivery of dirt as a part of the build process. You could also require hauling away rock as a part of the build process. It would take longer to build but allow placement anywhere that is flat.