Eki

This is actually something that can happen in our world too. It could still be more common on Roshar, but I'm not so sure.

Closer to 3600-3700 years after the WoK prologue, since Rosharan years are slightly longer than Scadrian years (which seem to be around Cosmere standard years). Since it's so long ago, that doesn't really matter though.

No, those two are the same.

I'd go for 3, but I agree there are some weird things we don't know yet. Radiants are chosen by spren. We don't know how they decide who to go for, but it seems to be different for different orders. People who have a cracked soul have the potential to become a Radiant. A cracked soul can be the result of emotional or physical trauma. Ultimately, it is the spren who decide if they will stay with the person, strengthening the bond between them. But it's also up to the Knight themselves to keep the oaths they've taken. So from what we can tell, the spren know that a Desolation is coming, and are searching out humans to bond. Basically in self defense. probably. Previously, they (at least most of them) had decided not to bond with humans anymore, because of the Recreance. Of course, we don't yet know why the Recreance happened in the first place...

It is assumed (at least by a lot of people), that Sazed meant two new base metals (and one new alloy for each of them). Those four existed before (and I think Mistings of those metals were born back then as well, though I'm not sure if we have proof of that), but they were so rare, and their existence so suppressed by the Lord Ruler, that no one knew about them. Just like aluminium, duralumin and electrum. And yes, atium was never supposed to be a normal part of the Allomantic table (nor was malatium), which is why gold and atium seemed so out of place. Atium is, as you say, Ruin's god metal. Atium was only produced by the Pits of Hathsin, which Kelsier destroyed in the first book. Most of the remaining atium in the world was burned during the final confrontation of Hero of Ages. As a side note, the bead that Elend ate at the end of WoA is Preservation's god metal - it is called lerasium, and it is very interesting. It's basically a solid version of the mists, or of the liquid that was in the Well. We don't know if atium is being produced again in the current era, but we do know that Marsh has some, which he took from a kandra in HoA. Compounding that is what he's been using to stay alive for so long. (Though some have theorized that Sazed is also giving him atium, if his original stash has run out). So that's why it's not in any of the current tables - most people don't know about it, and it isn't available. Even if it was available, we don't know if atium Mistings even exist anymore. I think they do, but that they'll just never find out. Others think Sazed changed Allomancy to remove them.

Rasarr isn't saying Dalinar made the marks, but that Renarin used Dalinar's knife.

There were older, more expensive bauxite refining processes too, so that doesn't necessarily mean anything. VenDell only describes the process as easy compared to the way aluminium was gathered before the Final Ascension.

Aluminium was rare for a long time in our world too, because it's hard to extract from bauxite ore. That is, until a certain process was invented, which made it much, much cheaper. I don't think we know if that process has been invented on Scadrial yet. So aluminium could become much cheaper regardless. Still, good point!

This is the most common theory, yes. Although I think some have theorized that they could be a mix of different civilizations, rather than only from Scadrial.

Szeth's response at the end of WoR doesn't match either of the two reactions we've seen Nightblood induce in people. He didn't feel nauseous, but he didn't feel compelled to possess it either. That could just be because he was in shock after having died and stuff, or it could be because Nightblood had already started bonding with him before he even woke up. Iirc, that stops both effects. (We know for sure it stops the nausea, because of events in Warbreaker.)

The force opposing Adonalsium is very likely to just be the group who decided to Shatter it. The way the question in that WoB was worded gave Brandon a lot of wiggle room. There is a second WoB where Brandon clarifies that "force" could mean many different things.

Ah, I didn't realize they had already begun floating at that point... I guess my idea would still work, but it's less likely.

Assuming Lashing another object takes as much stormlight as Lashing yourself, it would use just as much as if Szeth had used the stormlight himself, in total. So no difference there, compared to the theory that Szeth could Lash himself. It would require some trust, yes, but if those Skybreakers really wanted Szeth dead, they could have killed him pretty much whenever, by Lashing him into the sky against his will. That would, however, clearly be illegal, so the Skybreakers wouldn't do it. But it's also likely, as Yata says, that they just don't know Szeth doesn't have a spren (except for Nightblood).

As long as the Skybreaker never let Szeth go, but kept a hold of him all the way, I don't think it would be that dangerous.