"Until the earth passes away"

Today Elizabeth was telling me about her "bestest doll," her favourite, the one she wants to "keep forever and ever until the earth passes away."

That surprised me a bit. "'Until the earth passes away'?" I repeated.

"Yes," she said.

Later I told Sarah about this. She laughed, and related the following conversation she had with Elizabeth the other day.

Sarah: "Elizabeth, everything we have is just junk."

Elizabeth: "No, it isn't!"

Sarah: "Yes, it is. It's just junk, and it's going to burn up."

Elizabeth, dismayed and alarmed: "Why?"

Sarah: "Because it's junk. We didn't bring it in, and we're not going to take it out. It's just going to burn up."

Elizabeth thought about that for a minute, then asked, "But I can keep it until it burns, can't I?"