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Comment by thehappypm | Hacker News Reader

Basically, it is eroding a miniscule amount, and re-forming at a smaller miniscule amount. All of which well under the max 1mm/year.

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This information is irrelevant without knowing the current size of top soil.

Also important is whether the erosion is accelerating, constant or decelerating.

There was almost no erosion before modern farming, say 120 years ago. The high rates of erosion are a purely man-made phenomenon

On geological timescales the rate of erosion is almost instantaneous. We're talking about running out of topsoil in a single lifetime.

Without modern farming most people wouldn't be able to eat. Soil erosion doesn't worry me nearly as much as the constant transformation of farmland into crappy suburban developments, with pretty lawns that contribute nothing to the eco system or food supply.

And no one talks about the overpopulation enabled by the petrochemicals and the Green Revolution.

Those numbers are easy to find on google! Iowa 14-18" average topsoil depth in 1900, 6-8" in 2000. I'm not sure anyone could tell acceleration/deceleration over this timescale.

And topsoil is not very significant anyway. Corn doesn't need it, much.

My field was eroded clay when I bought it 20 years ago. Left fallow (well, planted in cover crops) it now has 4" topsoil. It can also rebuild you see.

Except that the USDA limit may well be wrong since it turns out pre-agriculture erosion rates were 25 times lower than the 1mm/year.

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