I probably just overlooked it, but where can I find an explanation at to what each of the ??-class end-of-the-world scenarios entail?
I don't really think there is one. I know XK means we're gone, the earth is gone and shit is ruined, CK is basically a mass extinction event, but the planet is still viable for life, I think.
Yeah, sure, here it is: [DATA EXPUNGED]
No, there's no hard-and-fast definition of either; like much of Foundation, it's left to the imagination. XK is generally taken to mean: "Oh fuck, this is the end of everything." I think CK only came up in one story, so you'd have to find out about that.
In any case, you're not going to find a specific definition.
I think CK-Class is a restructuring event, involving major alterations and/or damage to reality itself.
But yeah, the different scenarios are left deliberately vague, just to signify a variety of worst-case scenarios.
If I had to guess I'd say XK stood for eXtra Keter!!!! But I'm just guessing. I've always liked that the Foundation had a ratings system for end-of-the-world scenarios. I don't know if I'd like to see it codified the way Safe, Euclid and Keter are though. Some things are better left expunged.
Something kinda funny. So today I've kinda taken to reading the 'discussion' pages on different SCPs and I was reading the discussion for 225 and there's a whole conversation about xk and other end-of-the-world scenarios.
I can understand the reason for leaving it vague, but maybe there should be some kind of standardization for writing purposes. Like first letter is the type of scenario (viral outbreak, environmental contamination, temporal paradox, etc.) and the second is the potential for recovery (likely, unlikely, total destruction).
I know my idea will be rent asunder, but I'm just throwing it out there.
XK was originally a designation for a "end of earth" scenario in keeping with or as a direct result of a major religious event or artifact. It grew to mean more of a "salted earth" sort of situation, so it's a good example of a concept evolution.
I always took the letter designations to be some kind of very cryptic acronym. Such as my (sole) contribution to the XX-Class scenarios, the DG or "Dead Greenhouse" situation, where there has been a near-total loss of containment, and life as we know it is 80% or more dead, but the planet can still be fixed, more or less.
In canon, such as it is, it's easy to see how these things could be VERY unregulated. Speaking as a former cube-slave, policies change a LOT, and for very little reason. Systems are upgraded, replaced, or phased out. Management has a "new filing stratagem", Updates based on new information…it doesn't take much to muck up a naming convention. It's easy to say that the somewhat jumbled systems may be the result of rapid policy change, and some file sections just didn't get updated in the switch.
Incidentally, and totally off topic, this brings me to how I wedge the SCP website itself in to canon. The Foundation is undergoing a updating with the times. Their former all-paper records are all being scanned and placed in to a central database for ease of access in emergencies…and someone in that chain is collecting and dumping copies on to the public at large. Why? A very fun question…Agent gone rouge? Some faceless office flunky who wants the world to know? A MC&D mole spreading 'product information' on to the public?