I looked it up on Wikipedia and found a link to a Dune timeline that's defunct but preserved on the Wayback Machine site:
I haven't read any of the later books, nor have I read the original Herbert ones in decades. I was just trying to find some commonality to the 'Verse, and the absence of an inhabited Earth was the only possibility that presented itself other than the psi powers.
As for aliens, I thought the Guild Steersmen were aliens. Are they just heavily engineered humans? Anyway, if sandworms exist on Arrakis, there must be a whole ecosystem there; obviously no single species can survive in isolation. At the very least, there are sand plankton.
And don't give me that "not part of his vision" line. The stuff I've written for Star Trek
wasn't part of Roddenberry's vision either. All that matters is whether something is good or bad. Purism is an illegitimate basis for determining quality.