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Old 05-17-2014, 09:14 AM   #11
Genesis
 
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Default Re: [Space] Panspermia and the Campgaign

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Originally Posted by Nereidalbel View Post
Planets being habitable is not explained be panspermia; that's just being the right distance from the parent star. As for being able to eat plants on other worlds, that's just luck. Billions of years of evolution are more than enough to create large differences, as well as planets having differing chemical compositions.
It's worth noting that most of the things on this planet aren't edible. Of course, that's partly the result of a billion-year arms race between things that like to eat and things that'd rather not be eaten.

I think panspermia is a perfectly fine explanation for having compatible biochemistries on neighboring planets, in a "soft" sci-fi game. As a rigorous theory it has numerous problems, but so what? Rule of Cool it for maximum campaign enjoyment.

If you want to make it a little more rigorous, you can always opt for "Ancient Astronauts" notions - an ancient civilization developed space travel, seeded the system, then collapsed (for whatever reason... space plague? Gamma ray burst? whatever). Leaving the descendants of the organisms they brought with them on all the worlds they visited. Some places look just like the earth-analogue, some look quite different. You can posit intelligent life, closely related to humans (as the descendants of old colonists, sent back to the stone age and unable to bootstrap themselves up to UT without fossil fuels left by past epochs that didn't happen on non-earth-analogue planets), or not. It's your game!

A more serious answer to your questions: Unless they're evolved for it, you're not going to get terrestrial seeds clinging to meteorites. On the other hand, what's to stop the whole system from being seeded by some exterior source specifically evolved for interstellar distribution? Lots of fiction has space-based organisms, or organisms with a partly space-based life cycle. Something like this: a great interstellar tree approaches the main star of the system eons ago, but is shattered by a rogue planetoid. Pieces of its destroyed body, with all the attendant microorganisms, parasites, and symbiotes that usually ride with it, fall to ground on most of the planets in the system. The great tree is gone, but conditions on the proto-worlds are similar enough to the host for some fraction of attendant life to survive. Everything gets seeded at the same time, all the biochemistry is roughly similar, and when intelligent life evolves on of the planets it finds that its neighboring worlds are strangely (or not-so-strangely, probably, from their perspective) hospitable.

As for the sentience problem, it's only as much of an issue as you want to make it. As another poster mentioned, we've been on this planet for several billion years (for a loose definition of "we") and only one technological species has evolved in all that time. So hey, if you don't want there to be sentient species on the other planets, there aren't. If you do, then there are. it's your game, and either is just as reasonable as panspermia in the first place.
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Old 05-17-2014, 09:29 AM   #12
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Default Re: [Space] Panspermia and the Campgaign

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Originally Posted by Flyndaran View Post
Magic 8 ball: Answer hazy, ask again later.

We have one world known to have life. And only one intelligent species on that world in the past 4.54 billion years. We can't know much other than it seems that human level sapience is damn unlikely.
Well, only one intelligent species, by certain standards, and of which we know.

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Old 05-17-2014, 11:48 AM   #13
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Default Re: [Space] Panspermia and the Campgaign

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Do you have a cite for that? I just finished a graduate level class in meteorites, and ALH84001 has unequivocal Martian isotope ratios, not terrestrial. The 'fossils' are controversial, not the origin.
I'm sure it didn't go from Earth to Mars and back (there's no real mechanic that would allow rocks to be ejected off of Earth), but you'll get a significant number of meteorites that have been colonized after landing.
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Old 05-17-2014, 11:50 AM   #14
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Default Re: [Space] Panspermia and the Campgaign

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I'm sure it didn't go from Earth to Mars and back (there's no real mechanic that would allow rocks to be ejected off of Earth), but you'll get a significant number of meteorites that have been colonized after landing.
Large impacts have no issue launching rocks at escape velocity. So, yes, the mechanic certainly exists.
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Old 05-17-2014, 11:53 AM   #15
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Default Re: [Space] Panspermia and the Campgaign

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(there's no real mechanic that would allow rocks to be ejected off of Earth).
It's my understanding that there have been several impacts in Earth's history powerful enough to launch rocks into space. The dinosaur killer, for example.

Also large volcanic eruptions like Tambora.

Is that incorrect?
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Old 05-17-2014, 12:30 PM   #16
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Default Re: [Space] Panspermia and the Campgaign

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Originally Posted by Nereidalbel View Post
Planets being habitable is not explained be panspermia; that's just being the right distance from the parent star.
That's not the whole story; pre-life Earth did not have a breathable atmosphere or surface water and you can see how Venus has a similar distance from the sun but a very different condition from earth's current one.
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Old 05-17-2014, 12:34 PM   #17
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Default Re: [Space] Panspermia and the Campgaign

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Originally Posted by Flyndaran View Post
We have one world known to have life. And only one intelligent species on that world in the past 4.54 billion years. We can't know much other than it seems that human level sapience is damn unlikely.
What standard of "unlikely" are you applying? I think you could just as well say we know of one life-bearing world, and that world has human-level sapience, which is a 100% probability. You have to define your sample space, and the sample space of planets about which we have substantial information is quite small.

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Old 05-17-2014, 12:36 PM   #18
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Default Re: [Space] Panspermia and the Campgaign

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Originally Posted by Nereidalbel View Post
Planets being habitable is not explained be panspermia; that's just being the right distance from the parent star. As for being able to eat plants on other worlds, that's just luck. Billions of years of evolution are more than enough to create large differences, as well as planets having differing chemical compositions.
There are lots and lots of plants here on Earth that will kill you, quickly or slowly, if you eat them. In fact there are plants that have evolved chemical compositions specifically to make them toxic to plant-eaters; it's a common passive defense strategy.

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Old 05-17-2014, 12:45 PM   #19
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Default Re: [Space] Panspermia and the Campgaign

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That's not the whole story; pre-life Earth did not have a breathable atmosphere or surface water and you can see how Venus has a similar distance from the sun but a very different condition from earth's current one.
Breathable to us? No. For anoxic life? It was perfect!
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Old 05-17-2014, 01:41 PM   #20
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Default Re: [Space] Panspermia and the Campgaign

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It's my understanding that there have been several impacts in Earth's history powerful enough to launch rocks into space. The dinosaur killer, for example.
Hm. I may have overestimated the difficulty, it looks like at least some astronomers think it's possible.
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