Here’s a question an uncle of mine asked me today-
Why is it that old stuff - whether it’s medieval villages, ancient cities, or even fossils etc… ends up deeper and deeper under the ground? What’s the process whereby these layers of soil, rock etc… end up covering things over as the years go by? In thousands of years will people be digging down looking for remains of our civilisation?
Oliver
I pondered your question yesterday, as I dug a brick corner post out from under a huge mass of ivy that had grown over it. The ivy had been growing for years, and a little layer of topsoil had even formed on top of the post, which I had to brush away after I pulled the ivy off.
Plants. Plants grow up over things, cover them up, and then die and decay and become soil. So yes, if left untended, our own civilization would one day be covered up with plants and ultimately buried under the soil they leave behind.
Think of it this way: there aren’t many remains of the stuff that didn’t get buried. Most ruins that din’t get covered up were torn down for spare parts.
Also, on a larger scale, no landscape lasts more than a couple thousand years. Shifting wind and water table patterns, erosion, etc, cause the earth to move around. If, over a thousand years, a hill essentially moves from one place to another, it’s going to bury whatever is in the new place.
On the largest scale, this process is part of the tectonic plate systems of the entire earth. The planet’s mass is constantly switching places, via fault lines (specifically, subduction zones where one plate slides under another), and volcanic activity. As the lower part of the Earth’s crust moves down towards the mantle, freshly churned crust comes up to replace it.
Alessan, while vacationing in Israel a few years ago, I met a British college student who had a theory about the Romans: namely, that they didn’t actually build anything. They would just set down stones in a rectangular pattern and then go write a book about whatever building they wanted us to think was there. 
The Master speaks:
If you walk around out in the country, you may notice that there’s a ridge at the base of every fence row. Now, aside from the plant detritus that spoke- mentions, there’s erosion. Every wind on a dry day carries dust, and everything that sticks up into the wind stops that dust, so every obstruction makes its own island of dirt.
“Archaeologists; that’s them guys that digs the earth the most.” --Brother Dave
Archaeologists love crap. Trash heaps, shit pits, and abandoned housing yield more treasures than even tombs.
If you’ve read anything about the Roman Colis…Collus…that big old stadium, you know that there were three layers of other buildings on top of the original arena floor before it was excavated.