It doesn't have to go anywhere, it can just "die" - lose its ability to hold water, nutrients, fungus, microbes - everything necessary for it to be beneficial to plants.

So they've done what's all too common these days... gone and changed what a word means.

Dead topsoil is dead topsoil. It doesn't become rock or subsoil or something else.

The title of this post is "corn belt has lost a third of its topsoil". It should be "a third of the top soil in the corn belt is badly degraded" or something like that.

Have they? It's common vernacular to say we lost something even if it isn't "i lost my keys" but "We lost the last dodo bird"... doesn't mean we can't find it, but, what we had will never be again.

Why would it never be again? The ingredients to making good topsoil aren't a mystery. The topsoil can be fixed.

In many cases of periods of time longer than humans live...

We're shitty stewards... I've seen jeepers drive over tundra and do donuts not realizing their burnouts won't recover in a lifetime and other morons see them out there and think it means they can follow suit and before long the entire basin is destroyed...

sure... it will recover... when humans are dead, or when we pull our heads out of our asses :)

If the soil is dead it isn't topsoil, it is just dirt.

No, topsoil is more than mere dirt, it is an entire ecosystem that lives in the soil. It takes 50-100 years of build up and fertilizer and very careful tending, with less than optimal yield, to turn lifeless dirt into healthy topsoil.

Well no. Just like a rainforest doesn't just fly in the wind to become a rainforest somewhere else if you burn it. Soil is a ecosystem, not a raw material.

Sure, soil is an ecosystem, but topsoil is the top part of that soil. The surface layer. If you bulldoze a rainforest, there's no more rainforest. But if you scrape away topsoil, you have subsoil, and you have a big pile of topsoil.

That was a spectacular analogy.

It gets eroded by wind and water, with the end result being at the bottom of oceans and lakes.

Where everything eventually ends up. In the ocean!