>I think this one site alone will teach us more about Mars than all of the Viking and Pathfinder landers together

Weren't you complaining about choosing boring, safe sites a few weeks ago...? :)

Seriously, the lapilli story sounds plausible -- I hadnt realized they were accretionary and that certainly explains them being so round and non-vesicular. How strongly cemented are they? Ie, could we try to break one apart by squashing it (if we find a sphere sitting on the hard rock), or are they plenty solid?

Lapilli can also apparently form in impact ejecta, though in the example photos I saw they were in a much more chaotic matrix -- thick breccia, nothing like the nice layers and beds it looks like we're seeing. One paper also argues they can form in landslides (rock dust, moisture, lots of rubbing and bumping for static charges, makes sense).

If volcanic, it does seem a bit odd that these deposits are so widespread, and so thick. I realize Nick's post was not focussing on the global picture, but if we ask how well it scales up, you sure need a lot of lapilli-producing eruptions to explain all of that light-toned layered rock around the planet! Or perhaps what's unusual about Meridiani is that you had conditions at one point to produce these cemented pebbles that are somehow hematite related, while most of the light-toned layered stuff is more normal ash/tuff beds without our little spheroid friends.

Anyway, it's way past my bedtime. I'll tune into the press conf tomorrow and see what the pros have to say.

A side note for Nick, that landslide lapilli paper I noticed argues that the slide in question was a CO2-suspended debris flow! The author claims (and has some cites) that slides involving carbonate rock will generate gaseous CO2 by pulverizing and heating the rock, driving off CO2, in quantities large enough to help support the flow. Whether that is well known, a clever idea, or sheer rubbish, is beyond my ken, but here's a cite: http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_42550.htm