Turning a destructive edit into a layer

At the end of the previous exercise I promised to show you how to create…marquees of specific sizes, and I will do that, it's a very useful technique.…But it dawns on me in the meantime that I've made a dreadful mistake.…I've gone ahead and permanently modified the color of pixels here on the…Background layer, which is such a rookie error, especially for somebody who has…been using the program as long as I have.…However, I want to show you a great trick for retaining your changes, popping…them onto a new layer, without having to redo all that work.…So if you've made that same mistake I did, if I led you down the garden path,…then here's what you do.…

You start by going up to the Window menu and choosing the History command, which…brings up the History panel.…I want you to go down to this last state, which in my case is called Deselect,…because the last thing I did was deselect that circle, and I want you to click…in front of it in order to set Deselect as the Source History State.…Then, go up to the File menu and choose the Revert command or press F12, and…