Help with the meaning of the last line, "O-Lan...you are the earth."

Any thoughts?

I was sure I'd be able to find something on the internet about this, but all I seem to be able to find is regarding the book, and as far as I can tell (and I may be wrong) this line is particular to the movie's ending, not the book's.

I'm curious as to the logical interpretation of this line--I would think that, in the end, O-Lan would have proven herself to be reliable, loving, lavishing, and long-suffering, but I would also think that Wang's view of the earth is that it is fickle, liable to betray you at any time for no reason, and demanding of everything you have. These two portraits are incompatible if Wang is comparing O-Lan to the earth...is he changing his mind about the earth, or about O-Lan?? I don't quite understand why he would say this. (Although it is undeniably a beautiful line...up there with my all-time favorite, from A River Runs Through It, "I am haunted by waters." *shivers*)

Any help would be appreciated! :)