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There are two competing theories about the plenitude of intelligent life in the universe.  The first says that Earth and the solar system appear to be prototypical of some pretty common planetary systems throughout the universe, so there must be other planets where intelligent life has evolved similar to Earth.  We should be actively trying to find and communicate with them.  This theory was espoused by Carl Sagan and Frank Drake in the early 60s, who famously predicted tens of thousands of communicating civilizations in the Milky Way galaxy and created the SETI program to find them.

A competing theory, espoused by Peter Ward and Donald Brownlee in their book “Rare Earth: Why Complex Life is Uncommon in the Universe” claims that the factors that enabled intelligent life on Earth are actually not common, so there will be few if any other communicating species on other planets in other star systems.  They do not claim that life is rare, carbon-based life is probably very common, but the factors that enabled simple life forms to evolve into a species with brains and communications tools on Earth seem to be remarkable and unlikely to have occurred in other star systems.

Ward and Brownlee enumerate the following factors that were important, if not critical, to the evolution of intelligent life on Earth:
  •  The location of the sun in the galaxy – close enough to the center to benefit from nearby supernova events necessary to create the matter that seeds the planets, but not so close that constant bombardment sterilizes the planet frequently
  •  The size and brightness of the sun – smaller stars may not yield sufficient energy to provide an effective energy source for an evolving planet, but larger stars might burn out before an intelligent species could reach maturity
  •  An evolving planet with adequate size and composition (hydrogen, oxygen, carbon, iron, nitrogen, etc.) to provide the elements of life (whereas a smaller planet might enable life, a larger planet might generate too much gravitational attraction to permit species with calcium-based skeletal structures)
  •  An evolving planet in a circular orbit in a stable habitable zone where water exists in liquid form over billions of years – note that if the star is too small, the habitable zone may locate the planet in a tidally locked orbit, much like our moon or the planet Mercury are phase locked with their orbital centers, which would not permit day/night cycles, or seasons, which have clearly influenced the evolution of life here
  •  An evolving planet with a moon to stabilize its orbit over billions of years
  •  An evolving planet with another massive planet in the star system, similar to Jupiter, that captures through its gravitational field much of the debris that could sterilize the evolving planet over time
  •  An evolving planet with a system of plate tectonics that provides a long stable period of planetary evolution and enables biodiversity, which has clearly driven the evolution of intelligent life here
  •  An evolving planet with an internally generated magnetic field that repels cosmic radiation, which is harmful to cell function and likely a show-stopper for evolution
  •  A modest number of mass extinction events – enough to wipe the slate clean and restart whenever evolution results in dead ends, but not so many that intelligent life doesn’t have time to evolve

These factors don’t even consider the importance of the time window – in order to observe other intelligent species, they would have to be in relatively similar states of evolution coincident with us, and would have had to maintain their civilization long enough to remain coincident.  (This begs the question of how long Earth can sustain an intelligent communicating species before war, famine, climate change, celestial debris, or some other extinguishing event terminates it.)

Another factor that Ward and Brownlee don’t mention is the time and frequency scale that we take for granted on Earth – units of seconds, hours, days, years, generations, have developed on Earth relative to specific physical constants, including rotational and orbital frequency of the Earth.  Species on other planets may have evolved with generational cycles on the order of milliseconds or millennia, and we would likely not be able to communicate with those species on any reasonable basis.

Just consider the 24-hour rotational period of the Earth.  This period provide a centripetal acceleration at the equator that is not present at the poles, and results in an effective decrease in a body’s weight at the equator by a fraction of a percent.  But if the rotational period were 90 minutes instead of 24 hours – not that much different on a cosmic scale – then centripetal acceleration at the equator would exactly counter gravitational acceleration and would cause bodies to fly off into space.  (Has anyone considered that that might be the source of the rings of debris around some of our outer planets?)  I would argue that a planet where mass, including liquid water, is constantly being ejected is not a likely candidate planet for intelligent life to evolve.  

These are some of the important factors that characterize Earth and the solar system, and that suggest that we may be unique in the galaxy, and possibly in the observable universe.  Personally I find the Ward and Brownlee arguments persuasive, so I believe it is highly unlikely that we will ever find communicating alien civilizations trying to reach us.  The search for new Earth-like planets and for evidence of life elsewhere in the extraterrestrial universe is exciting and is likely to bear scientific fruit, but is probably not going to result in any buddy planets with aliens for us to adopt as pen-pals.

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Comment Preferences

  •  Tip Jar (20+ / 0-)

    'Tis with our judgments as our watches, none go just alike, yet each believes his own. - Alexander Pope

    by liberaldad2 on Sat May 24, 2014 at 01:03:37 PM PDT

  •  Can you please cite for this statement? (3+ / 0-)
    Recommended by:
    liberaldad2, Neuroptimalian, G2geek
    An evolving planet with a system of plate tectonics that provides a long stable period of planetary evolution and enables biodiversity, which has clearly driven the evolution of intelligent life here
    I don't believe I've ever seen anything citing the conclusion that plate tectonics leads to clearly driving the evolution of intelligent life.

    I'm not serious. Seriously.

    by IB JOHN on Sat May 24, 2014 at 01:33:31 PM PDT

    •  Ward and Brownlee address the importance (4+ / 0-)
      Recommended by:
      IB JOHN, 207wickedgood, rduran, G2geek

      Of plate tectonics on the unique characteristics of Earth.  I mentioned biodiversity - which provides a wealth of species, so you could argue just from a probabilistic standpoint that biodiversity provides a richer array of source species to seed each evolutionary step.  Biodiversity also is a mitigating factor during mass extinction events, preventing catastrophic loss of critical species, which clearly provides more opportunities to recover. W&B also mention the importance of plate tectonics on CO2 levels, which maintains a stable temperature over billions of years.  Also plate tectonics create continental features, which also encourage biodiversity (e.g., mountains vs freshwater lakes vs deserts).  Were plate tectonics to stop, the continents would erode and subside back into the oceans, so evolution would compete with extinction on land and would shorten the time before land species could evolve intelligence.  Complete speculation, of course.

      'Tis with our judgments as our watches, none go just alike, yet each believes his own. - Alexander Pope

      by liberaldad2 on Sat May 24, 2014 at 02:16:18 PM PDT

      [ Parent ]

      •  tipped & recced, and also... (3+ / 0-)
        Recommended by:
        liberaldad2, subtropolis, Lawrence

        a)  Even though I don't agree with W & B's conclusion (about which more in a moment), discussion of space science is important.

        b)  I was skeptical of the item about plate tectonics, but your explanation of it makes sense.

        Re. conclusions:

        I agree that as life becomes increasingly complex it also becomes increasingly rare.  Complexity is theoretically and empirically related to favorable conditions over sufficient time.

        However I think it's a stretch too far to assert that we are unique, as in "no other intelligent life in our galaxy."  

        SETI has only been active for 50 years, and we've only been discovering planets for a short time.  I think it's highly likely that any civilization that has attained an interstellar presence, is also going to use more efficient means of communication that we can't detect from here.  One obvious candidate would be modulated lasers between their various inhabited planets.  Another (speculative) might be something we won't understand until we've advanced further in physics.  

        Once we find the first example of another intelligent civ, we'll be in a better position to look for more.  At that point it's anybody's guess.  

        If I had to speculate, I'd say somewhere in the range of 1,000 to 3,000 in our galaxy.  And I'd also say that an upright terrestrial biped with limbs that have manipulative components (e.g. arms with hands) is probably a convergent plan-form for technologically capable species.

        We got the future back. Uh-oh.

        by G2geek on Sat May 24, 2014 at 09:36:43 PM PDT

        [ Parent ]

        •  I disagree with your conclusion (2+ / 0-)
          Recommended by:
          subtropolis, G2geek

          (Remember Fermi's paradox, after all.)

          But I agree that this discussion is important.  Thanks for your contribution.

          'Tis with our judgments as our watches, none go just alike, yet each believes his own. - Alexander Pope

          by liberaldad2 on Sat May 24, 2014 at 09:46:34 PM PDT

          [ Parent ]

          •  Fermi's paradox assumes "contact" (2+ / 0-)
            Recommended by:
            G2geek, liberaldad2

            … or, that we should be able to discern evidence for an intelligent civilisation in the signals coming at us from outer space. G2Geek addressed the signal question; the other can be countering by asking whether we should assume that anyone would want to reach out to us. Visit, keep an eye on things, sure. But initiate open dialogue? That there is fraught with all kinds of peril for both parties. It seems to me that Fermi, awesome guy that he was, was nonetheless assuming the White House lawn trope and all that.

            All things in the sky are pure to those who have no telescopes. – Charles Fort

            by subtropolis on Sat May 24, 2014 at 10:32:37 PM PDT

            [ Parent ]

            •  exactly. we don't spend much effort... (2+ / 0-)
              Recommended by:
              liberaldad2, subtropolis

              .... trying to communicate with every wild colony of great apes (gorillas, orangutans, bonobos, chimpanzees) we find.  Thus the signaling confound to Fermi's paradox.    

              Interstellar civilizations will probably have far-ranging science programs, but the effort they expend on any individual case of a life-bearing planet would be a function of the number of star systems they can research effectively with the technology they have.  One logical way to proceed would be to catalog the "interesting" star systems and then keep an eye on them for indications that their inhabitants have become spacefaring.  That assumption, in various forms, has been used widely in fiction, the film 2001: A Space Odyssey being the paradigm case.  There are many less-obvious ways to do it than by planting a device on a moon, for example by just monitoring the signal emissions from planets in the star systems in question.

              We got the future back. Uh-oh.

              by G2geek on Sat May 24, 2014 at 10:58:40 PM PDT

              [ Parent ]

          •  i'm inclined to believe that... (1+ / 0-)
            Recommended by:
            liberaldad2

            .... a) the signaling issue is a confound to Fermi, and b) "they" have other priorities for their science programs, than to communicate with every other intelligent species they can find.  

            Communication with a less-advanced species is interesting as a matter of pure research, but has little prospect that the less-advanced species has any knowledge that's useful to the more-advanced species.

            Communication with a more-advanced species has a larger potential knowledge payoff, but a comparably larger risk in revealing oneself to potentially hostile others.

            We got the future back. Uh-oh.

            by G2geek on Sat May 24, 2014 at 11:03:13 PM PDT

            [ Parent ]

    •  SPecific Points of Human/Hominid Evolution (5+ / 0-)

      are linked to specific plate tectonic events such as opening of the circum-southern polar ocean altering climate in Africa. There also seems to have been a really scary globally triggered bottleneck somewhere 50-70,000 years ago (not my specialty) that took us down to a few thousand individuals. This was shortly before some of our most modern behavior began to appear as I understand science for layman reporting these days.

      There's also the issue that with earth's tectonics also comes our molten core which brings us the magnetic field essential for keeping an atmosphere as thin as ours captive on a planet this small.

      The core in turn appears to be double, half or less contributed by the Moon-creating impact. Seems that most planets our size wouldn't have either plate tectonics or a magnetic field by now, and might be low on atmosphere and/or have too much radiation at the surface.

      As far as I can tell, everything learned about the earth beginning with plate tectonics has driven the Drake Equation answer far to the right of the decimal place, whereas almost nothing has shifted it to the left.

      For my money we're more likely to have visitors who use presently-seeming magical technology come out and acknowledge themselves before we get proof through light and radio data of a civilization anywhere else.

      We might find proof of multicellular life, for example an atmosphere such as ours that contains both fuel and oxidizer in quantities too large for stability without life processes pumping them in steadily.

      But a tech society may very quickly advance beyond spraying most of their communication energy out into the galaxy by accident, in which case to us they go dark after barely 1 century of visibility.

      We are called to speak for the weak, for the voiceless, for victims of our nation and for those it calls enemy.... --ML King "Beyond Vietnam"

      by Gooserock on Sat May 24, 2014 at 02:53:01 PM PDT

      [ Parent ]

    •  probably adds to diversity and makes logical sense (0+ / 0-)
  •  Given the huge number of star systems (9+ / 0-)

    in the galaxy and the seeming fecundity of life forms, it appears likely that other intelligent life must exist or have existed or will exist in the Milky Way.

    Given the vast time and space involved, the chance of two or more intelligent civilizations occurring at the same time and within hailing distance does seem very remote.

    Contrary to Hawking, I still think we should be on the lookout for possible contact however.

    •  Most Humans Lived for Half a Million Years WIthin (2+ / 0-)
      Recommended by:
      liberaldad2, too many people

      hailing distance but never knew the others were there.

      That would be today's hailing distance of course.

      We are called to speak for the weak, for the voiceless, for victims of our nation and for those it calls enemy.... --ML King "Beyond Vietnam"

      by Gooserock on Sat May 24, 2014 at 01:43:25 PM PDT

      [ Parent ]

    •  Hawking is on the lookout (2+ / 0-)
      Recommended by:
      liberaldad2, jrfrog

      That's to say, he's not not "on the lookout" for intelligent beings from elsewhere. It's probably not something that preoccupies him but he wasn't advocating that the subject be avoided. What he said was that, should they show up here we shouldn't assume that their intentions would be benevolent. For that reason we should also refrain from blindly sending signals into outer space in the hope that someone will notice. For it could well be that going unnoticed by that particular someone would encourage our survival.

      All things in the sky are pure to those who have no telescopes. – Charles Fort

      by subtropolis on Sat May 24, 2014 at 09:24:59 PM PDT

      [ Parent ]

  •  Perhaps, (6+ / 0-)

    Earth's tilted axis might make a difference as well.

    "The 'Middle' is a crowded place - that is where the effective power is - the extreme right and left might annoy governments, but the middle terrifies them." Johnny Linehan

    by northsylvania on Sat May 24, 2014 at 01:44:47 PM PDT

    •  Good point (2+ / 0-)
      Recommended by:
      koseighty, subtropolis

      I neglected to mention that the Earth's tilt creates the seasons, which contributes to biodiversity, adaptation, and lots of other factors that probably influenced evolution.

      'Tis with our judgments as our watches, none go just alike, yet each believes his own. - Alexander Pope

      by liberaldad2 on Sat May 24, 2014 at 02:21:02 PM PDT

      [ Parent ]

  •  Why are you assuming that we're intelligent? (11+ / 0-)

    We're currently in the process of making more and more of the only habitable planet we have, a hostile environment for the survival of our species.

    Sure, we can do math and science—but as a species, we don't seem all too keen to take math and science seriously when they interfere with our desire for comfort.

    Sure, we've figured out how to escape the evolutionary limitation of resources—but despite having the capacity to ensure that every member of our species has the means of survival, we allow some to hoard huge amounts while others starve.

    Would an observer from a species that developed interstellar travel or communication—which all but requires that the species progress past the point where they destroy the only environment that can sustain them—think that we're really all that intelligent? I find it difficult to answer in the affirmative.

    "When I give food to the poor, they call me a saint. When I ask why the poor have no food, they call me a communist." --Dom Helder Camara, archbishop of Recife

    by JamesGG on Sat May 24, 2014 at 01:47:31 PM PDT

    •  There are all kinds of philosophical implications (2+ / 0-)
      Recommended by:
      207wickedgood, akmk

      In your comment.  Would an intelligent species on another planet fall victim to the same influences that seem to be driving our own to extinction?  Are the traits that enable a species to survive and evolve in competition with other species early in their evolution also favorable to long-term sustainment at the top of the food chain?  Most importantly, is it inevitable that an intelligent species would evolve in such a way that intelligence loses its inherent survival value, to be replaced by stupidity and brute force in a resource-constrained environment?  I don't know, I don't think anyone does, but I hope we figure it out soon.

      'Tis with our judgments as our watches, none go just alike, yet each believes his own. - Alexander Pope

      by liberaldad2 on Sat May 24, 2014 at 02:31:48 PM PDT

      [ Parent ]

    •  Lots of space in space (0+ / 0-)

      With lots of crap we need to survive as a species.  The universe isn't that inhospitable, and now we can get at it.

  •  Well I've rarely felt alone. (4+ / 0-)

    Maybe driving through Lick Skillet, Alabama that one time.

    Best Scientist Ever Predicts Bacon Will Be Element 119 On The Periodic Table

    by dov12348 on Sat May 24, 2014 at 01:50:05 PM PDT

  •  The Earth is our only data point (5+ / 0-)

    so it makes sense to invert the question. Could any other intelligent species detect us? Certainly we put out enough energy in the radio part of the spectrum, kilohertz to gigahertz, but only in the last century, and so only within a hundred light years so far. There are no candidate planets for a civilization with technology comparable to ours or better within hundreds of light years, and SETI has detected no such civilizations within hundreds of light years. That's two strikes against the possibility.

    In Contact Carl Sagan had to invent a civilization with an FTL travel network that we could hitch a ride on, and the ability to place listening posts on uninhabitable bodies all over the galaxy, including one about fifty light years from here. That's a lot of supposition. Then he invoked a God with the superpower to change mathematics. Forget it.

    Over time, our signals would be detectable from further and further away. We could detect a radio-loud world like our own from several hundred light-years away, and we are building better and better radio telescopes all the time. We are reasonably sure that planets with life of some kind will exist in that range, but not a technological civilization.

    I would expect the reality to be somewhere in between the Sagan-Drake and Ward-Brownlee hypotheses. There are certainly plenty of planets of the right size at the right distance from suitable stars with sufficient lifetimes. We do not know that all of the other conditions that Ward and Brownlee cite are either necessary or rare. Gas giants are extremely common. Moons like ours are not, but might exist in modest numbers. We do not know what that all adds up to. All of the other requirements about size, location, composition, and so forth, seem to me to be fairly easy to satisfy out of the genuinely astronomical number of possibilities in a single galaxy.

    The biggest unknowns are the lifetimes of technological civilizations, and the future of technology. Our society is obviously quite fragile, given our abysmal track record of dealing with the consequences of new technologies in a timely manner, or at all. What we might invent in the future after the next revolution in physics we have almost no idea of, any more than our ancestors banging the rocks together could have thought of guns and bombs and rockets. But we can be certain that whatever it is, it will be weaponized.

    Back off, man. I'm a logician.—GOPBusters™

    by Mokurai on Sat May 24, 2014 at 02:01:44 PM PDT

    •  Minor quibble (5+ / 0-)

      In the Contact book, God did not change math. God showed proof of His existence through a detectable signature in a non-base 10 expansion of pi. I, however, see His Noodelyness in spahgetti.

      We need to continue to resist the notion that bullying is some sort of rite of passage. Bullying is killing our children, whether they are gay or "different" in other ways.

      by 207wickedgood on Sat May 24, 2014 at 03:37:46 PM PDT

      [ Parent ]

    •  not required to detect radio signals (0+ / 0-)

      Another civilisation out there may have noticed our blue planet a very long time ago. Just look at how many exoplanets have been discovered in the last decade. How long until we can examine their atmospheres? Our Earth could have been spotted millions of years ago. Imagine us uncovering a "Mesozoic Earth" out there. It's unlikely that we wouldn't keep an eye on it.

      Some people think that the flying saucer wave of the 40s and 50s was due to aliens discovering us because of our atomic explosions. I don't think they were discovering us at all; rather, we aroused their attention. If they exist, and can come here, then they've probably known about us -- or our bountiful planet -- for a very long time.

      All things in the sky are pure to those who have no telescopes. – Charles Fort

      by subtropolis on Sat May 24, 2014 at 10:18:04 PM PDT

      [ Parent ]

  •  This question is more complex than we think... (5+ / 0-)

    Granted the one thing that the possibility of intelligent life has going for it would seem to be the utter vastness of the universe.  There are so many stars and planets out there, in dozens of galaxies, that even if life is fairly uncommon, there's got to be somebody else out there.

    However, one thing overlooked in our search for Earth-like conditions is that life doesn't necessarily need Earth-like conditions.  The possibility of life forms unlike anything we know is something that we have to confront.  And the likelihood of that is greater than what you'd expect.  It was not that long ago that the black smokers were discovered on this very planet, forms of life living in conditions we expected to be completely inimical to life.  And yet, they have their own unique ecosystems.  I don't think it's so far outside the realm of possibility for life to exist in ways we don't yet understand, in environments which we could never live in.

    So, is there intelligent life out there?  Absolutely.  Will we ever meet or be able to communicate with any?  That is a much more tantalizing question.

  •  The recent finding that the nervous system evolved (7+ / 0-)

    at least twice on earth, once in comb jelly fish and once for the rest of the animals, indicates that multicellular life may be likely to evolve nervous systems. This seems to be more support for intelligent life.

    Humanoids have been around and intelligent for quite a long time, but only very recently became potentially detectable to a small fraction of the galaxy. One could imagine dolphins existing/evolving for many more millions of years and then going extinct, never leaving a detectable trace of their enormous brainpower. It is a slam dunk that other intelligent life exists, will exist, and has existed. The likelihood that it is close enough, technological enough, and brave enough to try to communicate during the brief time window available, is small, IMO.

  •  we ARE alone (2+ / 0-)
    Recommended by:
    rduran, liberaldad2

    Your list gives some of the pieces, but fails to put it together coherently.

    The most important thing is a planet with a very strong magnetic field.  Any star capable of producing enough energy to create life will also produce much more harmful energy that will destroy it.  So that radiation must be filtered out.

    The moon is the key, but it has nothing to do with "stabilizing orbits".  Venus has no moon, and it's orbit is just as stable as ours.  The most important factor in the creation of life is boosted iron and radioactive content from a planetary collision.  The normal accretion process will never cook up a planet like Earth, there must be a collision.  The plate tectonics we have is a direct result of this primordial collision, and retaining a vestigial mass in orbit.  The sizes of the bodies, and the dynamics of the collision must be just perfect.  For this reason alone, the chances of there being other macroscopic life in this galaxy is zero.

    That incredible improbability must be compounded by another improbability of just the right amount of "instability" - another collision, at the right time, to destroy the "population II" macroscopic life (dinosaurs), to allow the rise of Population I life (mammals), because dinosaurs would never evolve intelligence.

    This perfectly arranged collision comes from a well- behaved Jupiter, and planets like Jupiter are not well behaved.  Jupiter was probably tamed by another ridiculously improbable event, the early expulsion of a large planet(s) from the solar system.  There are almost certainly critical and improbable events that happened that we can never know about.

    Even finding slime somewhere in our galaxy is extremely unlikely, those "extremophile" arguments are bullshit, because those weird worms living around volcanic vents would never appear without a vibrant ecology going on above.

    I think there probably is intelligent life elsewhere in the universe, but the sad(?) fact is, Einstein has guaranteed we will never, ever meet.

    america is a great country. Too bad it's full of americans.

    by swok on Sat May 24, 2014 at 03:26:44 PM PDT

  •  One other unknown: (2+ / 0-)
    Recommended by:
    liberaldad2, JeffW

    the probability we can discern signal from noise.

  •  People forget the inverse square law (6+ / 0-)

    There's much comment, including here, that we as a planet have been producing radio spectrum waves for about a hundred years so someone must have "heard" us by now.

    People tend to forget that as those radio waves spread out, they get less powerful. This is not at a steady rate but obeys the inverse square law.

    Let me explain. If you measure the received strengths at 1Km from a transmitter and compare it with greater distances, you will find at 2Km the power is not half but 1/4. The equation is 1 divided by x squared where x is the relative distance. So at 1000Km the received power is one millionth and so on.

    At astronomical distances, the intensity is so low it is difficult to tell it from the background.

    "Come to Sochi, visit the gay clubs and play with the bears" - NOT a Russian advertising slogan.

    by Lib Dem FoP on Sat May 24, 2014 at 04:32:17 PM PDT

  •  I read the book Rare Earths a while back (1+ / 0-)
    Recommended by:
    akmk

    and I recall that its conclusion was that there were, at this point in time, no more than a few tens to hundreds of extraterrestrial species at our level and beyond in this galaxy (Maybe only one - us). We would be in a time period where other rare earths were just beginning to have sentient life emerge and the next billion years might see a dramatic increase in such life forms.

    If that is so I fear, unless our bio-psychological psyche evolves into something better, for those other species that may be our moral superiors.

    A million Arcosantis.

    by Villabolo on Sat May 24, 2014 at 05:52:07 PM PDT

  •  I find these "we're alone" arguments ridiculous (1+ / 0-)
    Recommended by:
    Lawrence

    It's almost as if some people really WANT humans to be the only Intelligent species in the universe. Maybe it satisfies a religious need, or provides contrarian street cred. The fact is, all of these reasons W & B presented for how Earth is so special and unique and how these qualities are required for intelligent life are pure speculation. So far, we comprise a data set of exactly ONE, and that tells us just about nothing about what could be possible out there, especially because our current instruments for detecting extra-solar life are barely on line. I predict that people will deny the possible existence of other complex and intelligent life until the day we detect it, and probably long after then as well...

    "Tell the truth and run." -- Yugoslav proverb

    by quill on Sat May 24, 2014 at 06:46:02 PM PDT

    •  humans are not even the only intelligent species (3+ / 0-)
      Recommended by:
      quill, subtropolis, Lawrence

      on this planet...maybe not even the most intelligent

      that being said...the diary is an cogent reminder that we live on a unique planet for all the reasons stated and then some

      It takes a unique combination of conditions for life of any kind to evolve in any particular way

      Perhaps we shall find diversity of life elsewhere in the universe...but like us?...or how complex?...or how long lasting?

      Good questions for debate and discussion.

  •  “The universe is a pretty big place....... (4+ / 0-)

    If it's just us, seems like an awful waste of space.”

    ― Carl Sagan, Contact

    “My soul is from elsewhere, I'm sure of that, and I intend to end up there." - Rumi

    by LamontCranston on Sat May 24, 2014 at 07:19:59 PM PDT

  •  The earth and life existed before homo sapiens (2+ / 0-)
    Recommended by:
    too many people, Lawrence

    emerged. Human existence on the planet has been brief, relatively speaking to the age of the earth.

    Too bad humans are hell-bent on making their own quality of life and ultimate existence as a species even more brief.

  •  Fixed title: (2+ / 0-)
    Recommended by:
    DMentalist, liberaldad2

    'Intelligent Life in the Galaxy – Are They Alone?'

    /snark

    "The church of life is not in a building, it is the open sky, the surrounding ocean, the beautiful soil"...George Helm, 1/1977

    by Bluefin on Sun May 25, 2014 at 06:14:03 AM PDT

  •  We aren't alone. (1+ / 0-)
    Recommended by:
    liberaldad2

    We're just unwanted.

    Homo Sapiens, the mangy stray dog of the galaxy. Unwanted, unloved, ignored and unfed. Bad tempered, fights with others, shits it's own bed. Under quarantine until further notice.

    Those aren't comets, they are warning beacons to stay away.

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