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(Topsoil is full of microbes that love to munch away on organic material, and don't forget the earthworms.
Those earthworms don't get their calories from rock and clay!
Thus, topsoil does not accumulate like most sediment, by simply piling up.
In the case of erosion, the topsoil, of course, is removed.
Geologically speaking, any given patch of land is seldom in equilibrium for long.
Either it is collecting sediment or being eroded away, usually the latter. Water-borne sediment will be washed in from higher ground, perhaps hills and mountains hundreds of miles away.
Sudden changes in temperature will have a smaller effect on the deeper parent rock.
However, the deeper that soil gets, the more insulated the parent rock becomes to weathering.
The geologic history of the strata making up the Grand Canyon is as much a history of erosion as it is of deposition!
Consequently, a patch of soil cannot be older than the last local erosion--whenever that might have been.
Forget about billions of years of soil accumulation!
Where sediment is neither being collected nor eroded, soils necessarily take their mineral components from the underlying parent rock.