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View Diary: A Perspective on Life on Earth (74 comments)

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  •  The question of our rarity is a question of (0+ / 0-)

    statistical probability.  And since we have taken only one very non-random sample in the universe (us), we can't assign a probability to sentient life elsewhere until we either discover it (100%) or never do (something above 0%).  

    I am with you, mattakar, in accepting that the possibility that the sentience required to discuss these topics may be rare indeed.  When the Alvarez father-son team proposed the meteor extinction hypothesis in the early '80s, they also proposed an agent for a posited cycle of mass extinctions: a dim, distant companion star of the sun that they named Nemesis, which every some tens of millions of years would make a close enough approach to the outer bands of the solar system to perturb the outermost objects and send them hurtling in toward us.

    While the meteor impact has pretty clearly been identified (its long-submerged crater lies around the Yucatan and the angled impact is thought to have sent a life-scouring firestorm fanned across what today is North America), Nemesis almost certainly does not exist.  But it makes your point that if we were in a more active galactic spot, we'd probably not be here at all.

    We orbit a solitary sun, not one like our nearest neighboring triplet stars in the Centauri system - or like the majority of linked stars in our galaxy.  We are in the rarefied outer galactic reaches, not the densely packed center where the majority of our galaxy's stars lie.  And we are in a spiral galaxy, not one of the enormous elliptical ones that may not be as hospital to the heavy elements or the multi-billion years of stability that may be necessary to develop sentience.

    And when we look for reasons for that stability closer to home, we may also note that we are an inner rocky planet protected by 4.5 billion years of gravitational object-sweeping by four gaseous giant outer planets, and share our orbit with a pretty hefty moon, allowing our dual system to do a darn good job of sweeping out the inner system (billions of times).  Finally, the collision itself that created that moon which you mentioned redistributed the accreted formative elements of our planet quite explosively, and the tidal effects of that moon may also be an agitating propellant in our story.

    So all in all, if it should turn out that there is sentience elsewhere, that wouldn't surprise since the universe is so large; but it's also young (only 3 times older than our own planet!) so if all these ingredients conspired to make us unique, that wouldn't be so shocking, either.  Hey, like I said below somewhere: great diary.

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