Why is older stuff deeper in the ground?

Dear friends –

Why are artifacts from ages past deeper in the ground than newer things? Living in the UK, traveling in Europe, I see the buildings / statues / artifacts that are older are also deeper (10, 20 or more feet) than newer things. The older they are, the deeper they are. Dig around in London or Rome or Paris or Athens, and there’s layer after layer of history.

The only explanation I have read is that “the detritus of people living there has accumulated and eventually people build on top of that accumulation”. This does not make sense to me. How much detritus can there be? Human and animal waste should (99%+) should be devoured by bacteria. Back then, food didn’t get wasted, and few things actually got thrown away (other than broken pottery). We make a lot of garbage now, but we live in a historically unusual time.

So what else would cause this?

Now I have to start guessing … but I would really love to know.

Either dirt piles on top, or stuff sinks into the dirt.

If dirt piles on top, is it

  • Silt from flooding? (Most villages are near rivers for trade and water, and often in marshy areas). But even places in deserts are impacted.
  • Dust from wind? (But why doesn’t as much blow away as blows in?)

If stuff sinks in the dirt, then is it …

  • Earthworms digging underneath heavy stuff? Darwin suggested this by pointing out that he had boulders in his field that had sunk over the years.
  • Stuff just sinks in soil, maybe as water in the water table rises and falls?

Anyway, I’d really love to know the real answer.

Thanks for your invaluable wisdom!

  • Rich

Cecil addressed this question:

How come archaeological ruins are always underground?

Bacteria don’t consume everything - there’s always some material left behind. (Just think of your fireplace after you have burned wood).

Anyway, one of the major causes is intentional burying. Seattle is a little like that too - after a major earthquake early in the 1900s, the inhabitants bulldozed the rubble flat and built streets on top. You can take the Seattle Underground tour to see parts of it that are still accessible. This isn’t a new phenomenon - many of the older cities (Jerusalem, for example) have been conquered, flattened, and built on top of many times over the centuries.

You can also answer the question from a rhetorical perspective. How would it be possible for newer stuff to get under older stuff? It isn’t. There are only two possible scenarios: 1) nothing was buried or 2) new stuff goes on top of old stuff. There just isn’t anyway other way to do it.

Biological waste doesn’t vanish simply because it decays; it gets converted into bacteria and eventually into soil. Maybe a part of it gets converted into gases (carbon dioxide, methane, hydrogen sulfide and water vapor) but you’re still left with a residue. Cellulose, especially chips and splinters of wood, decays very slowly unless eaten by termites and such. Add in every ounce of inorganic material that gets disposed of: not just broken crockery but every time a brick, a building stone or a clay tile chips, you add another grain to the detritus. Cities tend to be net importers of material, and with a high enough population density dirt and waste accumulates faster than it is dispersed.

Anybody who has tried to control rampant plant growth in their back yard knows the answer. Plants grow, they die, they become soil, they bury things.

I have a brick corner post in back of my house. Ivy had grown over it and nearly obscured it. When I pulled the ivy off, I found that it had left behind an inch of soil accumulation on top of the post. Just the result of plant material accumulating and being converted into soil over a few decades.

To add to other answers that have been offered: human creations tend to stand above the ground. In most places on Earth, sooner or later wind comes along, carrying with it leaves, dust, sand, loess, etc. This material tends to drop out of the wind and accumulate wherever something is standing above ground level, as a result of the eddies set up in the wind as it is deflected. Over time, this will tend to help bury structures.

Fine snow in windy conditions will give a great demonstration; so will windblown fast-food wrappers in cities.

Minor nitpick, but Seattle hasn’t had their devastating earthquake yet. What you’re probably thinking of iss the Great Seattle Fire in 1889: Great Seattle Fire - Wikipedia

In the aftermath of the fire, they took the opportunity to do some regrading to make more level ground, resulting the old street level being underground in some places: Seattle Underground - Wikipedia Most of the actual debris from the fire was swept into the ocean, making a couple of extra blocks of waterfront.

While I admittedly have not read the above links, I’ve got some archeological experience and can tell you plant growth growing above objects then falling down over and covering them up seems to me to be the chief form of burying older things.

You should also note that this is a case of natural selection. You only find older things buried in the ground because there isn’t any alternative. Either the ground swallows them up, or the ground recedes from them. If the ground recedes from them the best you can hope for is that they will be accumulated on the surface. Certainly not to be snarky, but where would you expect to find older things? on TOP of newer things? Once you realize it is pretty difficult to put older things consistently on top of newer things, you can see there is only one alternative…older things just naturally fall to the ground first before newer things.

The rise of modern archaeology is fairly recent, dating to the mid-nineteen century. Before that, there just wasn’t widespread excavation of ancient sites. Plus, things that are shallower get dug up first. The deeper it is buried, the less likely to be dug up; conversely, the shallower things are buried, the less likely they will remain in the ground to become old. The result is, older things appear to be buried deeper.

Gravity does always sort heaviest to the center of the Earth. Unless it’s capable of independent movement material will sort it’s self out. The wetter the soil the easier this is. Running water and wind are also very good at burying anything. Don’t think flooding has to be near a river either. All you need is a deluge anywhere and you have a flood, Finally don’t forget the burying power of mud slides and earth tremors. No water and anchoring in soil and you get dust storms and we know how that worked out in the dust bowl. Dust storms can deposit material around the world. Sahara Dust Cloud Heads to Florida. Ultimately it all comes down to the gravitational attraction on materials being constantly sorted by the density of the material.

IIRC (from something on the History Channel), one of the basic principles of archeaology is that deeper equals older.

Uh…what? Are you seriously suggesting that gravity is the mechanism by which ruins are buried?

If materials were always sorted by density as you suggest, wouldn’t lead and gold objects always be deeper than other objects of similar date?


Yeah, that was what I was thinking of. For some reason, I thought the fire was linked to an earthquake like San Francisco’s.

We call it the Law of Superposition. All things being equal, the old stuff is at the bottom. If it isn’t then we have to figure out why.

I have experience of a very good example of this. Two/three years ago I worked on a a site in Swansea, Wales which consisted of, in reverse chronological order; an Addis plastics factory, a WWII munitions factory, a 19th C. copper works and, beneath them all a 18th C. copper and zinc works. Each of these complexes had been bulldozed with the debris from the walls filling in the voids left by the furnaces etc. thereby leaving a flat even surface for the construction of the new buildings. By the time all these layers of archaeology had been excavated and recorded we were c. 25/30 feet below the modern land surface. It was an amazing site with acres of upstanding archaeology, some of the furnace walls were 8ft high.
The study of the natural burial and subsequent decay of materials is called Taphonomy by the way, we studied it in my uni degree course.

:slight_smile: x

Turbulence in the stuff being moved will always mix stuff up some. The denser the material the faster it sinks, and a river bed is a good example of this sorting at work. Soil will allow the same over much greater periods of time.

Nope, not buying it. Cite?

Nope. I guess it can’t happen.

Some followup comments/questions:

As I understand it, the fusion in a mainstream star stops with iron. Ultimately the core of the earth is iron. But higher elements like gold can be produced by supernovae, and it ends up on the crust of the earth via asteroids/meteors/whatever. Which would explain why the core of the earth is not gold.


jeez louise, that is poorly phrased.

This process doesn’t even have to take that long. Have you ever been to an abandoned townsite? Or a town with large abandoned sections? I have. And I can tell you that even in a decade or two you start finding stuff buried under the ground. A house goes decrepit, the windows get smashed, the doors comes off the hinges (or are stolen or carted away, and plant life starts creeping in. in back, old tools or bits of old cars or whatever are grown over with weeds, which turn to mulch, which grows new weeds. Trees grow, and the roots destabilize the soil or grow around half-embedded bits of human flotsam.

Remember also, the old cities didn’t have the efficient garbage removal that we have today, and the people didn’t use as much throwaway, temporary material. If they had to leave in a hurry, they couldn’t take all of their possessions with them. So stuff tended to remain in place more so than it does today.

Today, if you need to knock down an old building to make a new one, you might hire a few trash removal trucks and use a front-end loader or a crane to pull up everything and dump it in the trucks and remove it. Now think about how hard that would be to do if the home was in the middle of a city in the 1600’s. Far easier to just build on top of it.