why is the floor level from the past always below what it is now?

Question

Whenever you see archaeology programs on telly they always dig down to reveal the past. So where did all the extra soil come from? Was the earth smaller back then? Is the soil just moved around over thousands of years meaning that there are loads of places where the ground level 1000 years ago was way above where it is now and so you can't do archaeology there? I know this sounds half-witted but my kid just asked me and I'm struggling to come up with an answer I can justify. Thanks

Answer 1

Dust accumulates, simple as that!

Consider a 1 mm accumulation of dust per month (a very conservative estimate!), then that would be 12 mm per year, or 1200 mm per century, or 12 m per millenium!

As dust accumulates in this way, it of course will have weight which literally presses down on underlying material, which will then be cemented into rock.

One may argue that a lot of dust blows away, etc. but on average dust does accumulate at a slow rate as argued above. The dust itself comes from erosion of existing earth surfaces, so there is a cycle of old dust being laid down, and new dust eroding, which maintains a net balance. Dust does not escape entirely from the earth, due simply to gravity.

There ARE places where an older layer may paradoxically be ABOVE a younger layer, but these are due to buckling of rock from tectonic deformation, and would be relevant only for layers that are millions of years old.

Answer 2

Land masses move up and down over time. If one sinks under the sea, you can get limestone and sandstone deposits on it. As the crustal plates move around, the land mass may be forced up again, so that it is far above sea level. Lots of beautiful examples at the US Grand Canyon in Arizona.

Answer 3

the earth is always moving and changing shape. when that big earthquake happened in indonesia some of the islands moved 6 feet from their orignal position. thats not much but it add up over thousands of years. just like the san andreas fault is constantly sliding north and south. but its to small to feel or see. and through time all those milimeters of sliding will become miles.

Answer 4

These things could happen:
1) stuff grows over it or through it, then decays slowly building up layers year by year.
2) buildings slowly sink into the ground
3) circulation of material by worms (or other subterranean creatures), water (or precipitation), freezing/unfreezing provides millions of opportunities for material to sink tiny amounts under its own weight.
4) people build on top of it
5) volcanoes cause massive circulation of material from inside the earth's core to the surface, effectively causing material to "sink" into the surface
6) agriculture causes farm animals to compact soil, causing it to sink to the lowest possible level (possibly iterating with 3))

I hope at least one of these is true!

Answer 5

Near the desert wind blows the sand over the top of ruins.

Answer 6

Well when i became an archiologyst back in the mid 90's they sayed no soup for you and fired me so dont know srry

Answer 7

Millions of tons of particles fall each year on earth.And vulcanos and deserts blow their stuff around the world.And organic material.

Answer 8

Global warming.

Answer 9

Because if it was in a layer that is above where you are now it isn't there anymore.

It only gets preserved if it gets buried and stays buried. Otherwise...no cigar.

Answer 10

Everything we make slowly sinks into the mud.