Organic matter collects and degrades into basically soil. I have bush that constantly sheds leaves. If I don't keep up with sweeping, they pile up. One pile I d

Organic matter collects and degrades into basically soil. I have bush that constantly sheds leaves. If I don't keep up with sweeping, they pile up. One pile I didn't get to for a very long time, and at the bottom of that pile was basically leaf dirt. Other things can get almost absorbed into the soil. Walk around an old neighborhood in your city, you will notice the edges of the sidewalks are being actively absorbed into the dirt along the sides unless the property owner is keeping up with edging.