Quote Originally Posted by Ascension View Post
At the extreme edge of plausibility you could have a giant earthquake swallow a whole continent, thereby pushing water levels up. Or you could have some volcano spew out some enormous amount of lava. Neither is all that realistic but it avoids giant craters and fires left over from impacts. My first thought was as Toff says...icy comets.
That's why I'm wondering about size of particle and where the residual matter ends up....if everything can burn up in the atmosphere, but the water end up within the atmosphere, I don't have to worry about craters - which, really, I don't want to do, as I've got the planet already designed.

I, obviously, should have mentioned that earlier.

Initially the planet will be fairly cold, with most of the residents located close to the ocean using it's energies to generate heat, food, etc.

There are several billion residents of a fairly old civilization.

Then the "incident" happens.

90% of population killed....water levels risen (covering up most cities)...in subsequent years, starvation, disease, nature's turmoil at massive climate change, kills of most of the rest.

1000 years later, scattered small groups survive, though almost all under 5 people (mostly family groups). They are hunters/gatherers/ and exist at an animalistic level in terms of survival of the strongest.

There's the nutshell of my prehistory - but I want to figure out this event before I move forward.