Why do archeological sites always get deeper underground with time? If ground gets on top of them, it must have came from somewhere else. Why no locations seem to rise with time, rather than sink?
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It depends on the area, but most dirt comes from plant decay. When a plant dies it is consumed by bacteria and fungus. What’s leftover are component of dirt. Even simple grasses on plains decay and add a bit of dirt. Over hundred or thousands of years of decay the little layers stack up.
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Stuff gets deeper over time as soil builds up on top of it. This can be from plants and animals decaying on top of the site and turning into soil, or the soil can arrive from wind, water, and other factors bringing it in from somewhere else.
Some locations do rise with time, which is how we get accessible dinosaur fossils on the surface even though they died millions of years ago. This happens when erosion removes soil from the site.
We see the former case much more than the latter because a layer of soil can preserve things underneath, while the factors that remove soil from a site can also destroy the site itself.
> if the ground gets on top of them, it must have come from somewhere else
This assumes there is a finite amount of dirt, which is a false premise. New dirt is always being created from dust and plant and animal decay. So barring some type of erosion or some type of physical removal, as time goes by, more and more dirt will accumulate everywhere.
Well because if the site is in a place that -didn’t- tend to get buried deeper over time, or possibly suddenly buried in an event, then later exposed, then there wouldn’t be an archeological site left to find at all as all the stuff should have gotten decomposed or weathered away.
What you are seeing is survivorship bias.
The pyramids are very old archaeological sites and they stick up well above the ground, as do many castles and cathedrals.
But, if something old is sticking up and looks like useful building stone, people will nick it to build farm sheds and things, so what’s left is things that are already buried far enough they’re not worth the effort of digging up or things that are too big to shift.
Lots of archaeology is of things that were already below ground level, like graves, ditches and rubbish pits, wall foundations, or floor levels that were cut into a terrace.
Things at ground level very easily get buried, like if a wall falls over or just from dirt and grass and weeds building up. Have you ever noticed how weeds and grass grow in cracks between pavers, and how dirt and mud build up in corners, and how much effort people put into sweeping and hosing and cleaning their buildings? Even things that are above the original ground surface get covered by plant growth until they’re mysterious lumps and bumps in the ground.
If dirt is being eroded from an archaeological site, the archaeology often gets destroyed. Coastal cliffs get worn away by waves and storms and suddenly there’s bones from a 1200 year old cemetery sticking out over the beach, and then they get washed away too. Rivers change course a lot, they could bury an old ship then expose it again centuries later, and then the ship quickly rots away.
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