[malloyd]

Originally Posted by scc

But from the look of things there might be a few problems with that. While Bacteria, fungi and other single celled lifeforms. But what about slightly bigger lifeforms, could plant seeds have made interplanetary or borderline interstellar trips clinging to the side of a meteorite?

Likely not, they'd burn off during reentry. They'd need to be inside the meteorite to have a chance. Which doesn't seem a whole lot less likely than the bacteria I suppose. Does it matter? Unless you have time travelers go back and look, or I suppose happen to turn up the records of the terraformers, you are never going to be *certain* where the life on any world came from.

And the big one: If I assume the planet that humanity evolved on is the one where life first arose on, the planet closest to that, at a mere 1.28 AU, has a high chance of have sentient or near-sentient life. What do people think are the chances of that happening?

We have no idea - the problem of extrapolating from a tiny sample. Once we have managed to look for life on more than two worlds, and found at least one more biosphere, we might be able to say something that wasn't a pretty much a guess. The lack of any evidence of a second sentient species evolving here on Earth at some point in it's history suggests the odds aren't wildly in favor of it, but really they could be anything from several percent per geologic period to, well, anything down to just above zero.

And what are the odds that people realize it before things are too late? And is any sort of communication possible?

With something genuinely intelligent, it's probably fairly obvious and some level of communication is just about certain, eventually. Near-sentient it's much harder to say, not least because that's an even harder to define concept. Again, does it matter? You are never going to get universal agreement - small sample size is against you again. Pick whichever one makes the campaign premise work better.