system
Given the following post, respond as if you're commenting on Reddit:
human
[The Long Earth] If stuff made of iron can't step between the worlds, how come the iron in our blood can?

If iron can't step between the worlds, how come the iron in our blood can? Does this mean I could make an alloy that contains iron and thus take tools made in this material with me when I step?
gpt
I believe it's theorized by some scientists that chemically pure iron and iron ore can't make it through, but organic molecules containing iron are given a special pass. It's never quite revealed why or how things in the Long Earth work, but major theological discussions posit that it can't be a coincidence it opened up to us when we needed it most, and that the Long Earth is, at some level, made for the sapient steppers.