Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Extra Terrestial Life Form

  1. Mar 4, 2016 #1
    Dear PF Forum,
    I would like to know if LIFE in exoplanet is possible. And if it is, how?
    When I drove my Pastor to my mother funeral, he asked me out of the blue while I was driving my car.
    "Do you believe there is another earth?"
    My immediate response would be, in parallel universe where there are Nicole Kidman, Megan Fox, Linday Lohan OR in this universe.
    "In this universe," he said.
    So there were the following problems I think.
    First, life should be in a planet or moon (as in Avatar).
    This planet must be supported by a nearby star.
    And for this star:
    I think the star cannot be too massive. I read that the comparisson between the mass of the star and its lifespan in main sequence is to the power of 3.
    For example, a 2 solar mass star will have 1/8 lifespan of our sun.
    10 solar mass star will have 1/1000 lifespan of the sun. That is: 10 million years.
    Earth develop life form in 3.9 billion years. "Only" in 600 million years ago (Cambrium) there were many multilcellular organism blooming in the ocean. Trilobite, nautilus, etc...
    And it takes 4.5 billion years for earth to develop intelligence.
    And the star cannot be too light, because if it's too cold, then the planet should be closer to the sun, then there are tidal lock problem, and radiaton.
    So how is the chance for this universe to have, IMHO, stars that are 0.8 - 1.2 solar mass?
    For these stars to have planet in their habitable zone?
    I'm not trying to bring Drake Equation, just want to lay out the facts.

    And after all those...
    What would that lifeform be?
    Will it be carbon compound? Since carbon has 4 valence and
    Abundance Element.JPG
    Carbon is abundance in the universe. I don't know if this number represents carbon in outer space nebulae, or locked in white dwarf stars.
    Silicon and Germanium have 4 valence, too. But since they are more complex than carbon, I think carbon is easier to build element compound rather than Si/Ge. And Carbon is more abundance than Si/Ge.
    And IF the lifeform in exoplanet is carbon based, would they develop DNA as their method to replicate?
    So my summary questions are these:
    1. Given those conditions, would extra terrestrial life be possible?
    2. IF it is possible, would it be carbon based?
    3. IF it is carbon based, would it develop DNA as their replication method?

    Thank you very much.
  2. jcsd
  3. Mar 4, 2016 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Is "LIFE" different from "life"?

    That's actually a different question: it seems very unlikely that there will be a duplicate Earth out there.
    Calculations based on the probability of getting life as in a duplicate Earth biosphere are misplaced.

    You mean "carbon based" ... few biologists would consider any carbon compound to be living.
    You should think of "live" as a class of emergent properties or behaviours arising from complicated processes.

    Carbon is abundant - it is the 4th most common element in the Universe.
    Life on Earth is built mainly from 5 of the 6 most abundant elements ...

    Id life possible off the Earth: almost certainly yes.
    There would almost certainly be carbon based life off the Earth somewhere.
    Among other approaches, there will almost certainly be DNA based life elsewhere in the Universe. You are probably thinking of "reproduction" rather than replication ... DNA is not the only replicating molecule: there are many.
    Look up "RNA world".

    Basically, we'd expect the stuff we identify as "life" to be really common and turns up pretty much wherever it can possibly happen. The basic molecules are common, and you have to try hard not to get life to happen. Organisms do not have to use DNA to pass heredity, they do not need to be carbon-based. As we explore our own solar system more closely we should be able to get clues that will give us an idea of how common life is. Whatever the future outcome, the lesson of history is that treating humans as somehow special in the Universe is not the way to go. Scientific progress is made when humans are removed from the central role in Creation: it's a fundamental and important humility in Science.
  4. Mar 4, 2016 #3
    Thanks Simon.
    Of course not. It's just an emphasis
    Yes, unlikely. That's why my immediate respond was
    I believe what my Pastor meant was "Do you think there is life in exoplanet?". But I think he's not much of a scientist, it's just a figure of speech.


    Thank you
    Thank you
    Thank you

    Certain? So the possibility will be very high.
    And was just wondering if the intelligence creature there would be humanoid.
    In the ocean, dolphin (and whales) and the extinct ichtyosaurs are fish like. Perhaps advanced life form under water is fish like.
    Perhaps intelligence life is humanoid? Although they may only have four fingers like ET.

    Thank you very much for your opinion Simon.
  5. Mar 4, 2016 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    I said: "almost certain" ... but yes, it is reasonable to expect the probability of there being life other than on the earth to be very high.
    You should be careful when religious people ask you about the probability if life, it is a common argument against evolution.

    The "humanoid" bodyplan is basically that of fish.
    There are many more bodyplans possible - iirc most of the bodyplans that have ever emerged on the Earth went extinct through being unlucky rather than being slowly selected out. So it would be unreasonable to expect this bodyplan to be strikingly present on exoplanets. The only reason it is so noticable on the Earth is that we have it too.

    We have to be careful about what we mean by "intelligence" too: we tend to define this term to suit ourselves and we may be a bit too smug about it.
    Looking around us even today there are many strikingly bright animals - maybe even some that are self-aware. Expecting a human-like intellegence, if it should occur, to appear in a human-like body plan seems like too much.

    Perhaps sure - but that's just empty speculation. The way to go is to ask if there is any special reason to suppose that intellegence prefers to appear in fish-like forms. You got to realise that the humanoid body plan is not even all that common on the Earth.
  6. Mar 4, 2016 #5


    User Avatar
    Staff Emeritus
    Science Advisor

    We really have no idea. But, have you ever taken a look at the Hubble Ultra Deep Field? There are somewhere around 10,000 galaxies in that picture. And it covers an area of the sky smaller than the full moon. So, given incomprehensible number of star systems in the billions upon billions of galaxies just in the observable universe alone, I think it would be extremely unlikely that life exists solely here on Earth and nowhere else.
  7. Mar 4, 2016 #6
    Yes Simon. But it's not the religious side that I want to discuss here in PF. It's just that I've never given thought of what would extra terrestrial life be. I often watch Startrek, Star wars, alien, etc. But never gave it a thought. It's just that last week I analyze.
    IF there is a life in exoplanet, what would that be. Carbon based, DNA, mass of the star, etc... It's really not about religion :smile:
  8. Mar 4, 2016 #7

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Didn't think it was - just raising awareness of an issue that plagues all too many of us.

    It's not a very big "IF".
    Like if you rolled 10 dice and got something other than 10 6's, you wouldn't be all that surprised right? Life is more likely than that. Much much more.
    So if someone said: "IF I don't roll all sixes..." ... well you'd wonder why the emphasis.

    Space is big, really big...
  9. Mar 4, 2016 #8
    One thing to keep in mind, Stephanus, that Simon Bridge has touched on: we only have one example of a biosphere. We are strongly influenced in our perspective on the nature of life by what we see on Earth. We talk of the Goldilocks zone, Earth like planets, carbon based lifeforms, water as the active solvent and present well reasoned arguments to support this focus.

    This may turn out to be the truth. However, I always caution about extrapolating from a sample size of one. The fact is that we do not know how common life may be, or how common intelligent life may be, or even if we might be the only planet with life in the entire universe. That just makes it interesting.

    If you would like to explore the topic more you might consider reading Rare Earth by Ward and Brownlee. Their conclusion: life is common, intelligent life very rare.
  10. Mar 4, 2016 #9
    So, the reason why ET haven't phoned us yet is that space is really big.
    I'm just wondering. Supposed, just supposed there's a civilization, say 100 thousands years more advanced than us, (star trek is only 300 years). They would have conquered any galaxies I think.
    And 100 thousands years are not really that much.
    But carbon based and DNA is enough for my curiosity. I just want to know that if there's life out there, how is the chance that it's carbon based. And if it is, how is the chance that it develops DNA.
    Thank you guys.
  11. Mar 4, 2016 #10


    User Avatar

    Staff: Mentor

    I'm not sure what exactly you mean by "how", but if life is possible here, why wouldn't it be possible on another planet with similar conditions?
  12. Mar 4, 2016 #11
    So, humanoid is not common. Okay
  13. Mar 4, 2016 #12
    That's what I want to know. Not in biological term but in mathematic point of view.
    How big is this "similar conditions" chance.
    And even if it's not "similar", just as @Simon Bridge says, it's likely carbon based and DNA. Thanks.
  14. Mar 4, 2016 #13
    Without actual empirical proof nobody can say with absolute certainty that life exists beyond the planet Earth. However, as others have already noted, the odds are so statistically high that some form of life exists beyond the planet Earth that it can be said to be "almost certain." Consider that we have discovered evidence of life on Earth as far back as ≈3.8 billion years ago. There does not need to be an identical Earth out there, just one that is close. Obviously the planet needs to be within the habitable zone of its star and have a sufficiently dense enough atmosphere to support liquid water on its surface. However, the atmospheric pressure could vary significantly, and there does not necessarily need to be a moon, or there may be more than one moon.

    Most of the main sequence stars (at least in the Milky Way) are spectral type M (76.45%), 12.1% are spectral type K stars, 7.6% are spectral type G stars, and 3% are spectral type F stars. Ideally, a main sequence star should be somewhere between 0.75 M and 1.25 M to give life the best opportunity to evolve for long periods, but as we discovered on Earth it does not take life very long before it gets started. In just under a billion years after the formation of Earth life had already begun. Therefore, it is possible for life to begin even under much higher mass stars, and thus stars with shorter life-spans.

    Approximately 60% of the main sequence stars in the Milky Way galaxy have planets. A much smaller fraction of these planets will fall within the habitable zone of their star. However, considering the number of stars in the Milky Way galaxy alone, a reasonable estimate would be ≈40 billion Earth-size planets within the habitable zone of their star. That would seem to stack the odds rather heavily in favor of life existing beyond Earth just in the Milky Way galaxy, and there are billions of other galaxies that we are not even including.

    There were multicellular lifeforms prior to the Cambrian. The Cambrian marks when arthropods evolved and a real diversity of life began, thus the phrase the "Cambrian Explosion." However, jelly fish and other soft-bodied multicellular lifeforms (including some forms of multicellular algae) existed for millions of years prior to the Cambrian.

    Therefore, while no one can say with absolute certainty - until definitive irrefutable proof is eventually found - one can say with "almost certainty" that life must exist somewhere in the Milky Way galaxy.

    http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2001JRASC..95...32L&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf [Broken] - Journal of the Royal Astronomical Society of Canada, Vol. 95, p.32, published February 2001.
    Last edited by a moderator: May 7, 2017
  15. Mar 4, 2016 #14
    Well, hydrogen, oxygen, carbon are abundant elements in this universe:
    Abundance Element.JPG

    I like it!
  16. Mar 4, 2016 #15


    User Avatar

    Staff: Mentor

    Are you familiar with the Drake equation?

    Even 20 years ago it was so wildly speculative that it was utterly useless (it is mostly a thought exercise), but since then we have learned a lot more about the universe. Including:
    1. 20 years ago, the Hubble Deep Field revealed that the entire universe is utterly filled with galaxies.
    2. We've learned that life seems to have arisen on Earth very soon after it became hospitable to our form of life.
    3. In the past 5 years, we've discovered that most stars have planets around them. We've only been capable of detecting the large ones, but it stands to reason that there are a lot of solar systems similar to ours.

    The one thing standing in the way of intelligent life that I can see is the fact that simple life existed on Earth for billions of years before complex life arose. So the jump from bacteria to animals may be more difficult than the start of life itself.
  17. Mar 4, 2016 #16


    User Avatar

    Staff: Mentor

    I watched a pretty decent TV documentary on the Webb space telescope and it appears to be the general conclusion of the scientists working on it that life elsewhere in the galaxy - and relatively nearby - is near inevitable.
  18. Mar 4, 2016 #17

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Nobody knows any reason life should not be almost certain someplace.
    As to the maths:

    I don't think anyone knows enough to put a number on the odds ... it's just that the odds would have to be extremely long indeed for there to be even odds that we are the only ones in the whole visible Universe ever. That's the sort of calculation you can do.

    You can also work out how likely the sort of life that the SETI project would have to be to give them an even chance of finding some.

    Using just statistics, this is the best you can do ... you need data from things like biology and astrophysics to get a better guess.
    See post #15 for examples.
  19. Mar 4, 2016 #18
    Read it yes. Understand it, no. But many people thought that Drake equation has too many unexplained variables. It's like Ferim problem in space.
    Carl Sagan once said that there are 100 billions galaxies in this observable universe. Care to tell me what is the estimate now?
    Yes. @|Glitch| says it's 3.8 billions years. But lately I heard that, as you say, life arose very soon after Earth became hospitable, perhaps after heavy bombardment period? But I just let his statement goes.
    Please confirm:
    From bacteria to animal is more difficult than from raw material to a single living cell? Because of statement number 2?

  20. Mar 4, 2016 #19
  21. Mar 4, 2016 #20
    I don't know how "near by," but I would not consider it unreasonable to say that the percentage is better than 99.9% in favor of life existing somewhere within the Milky Way presently, and much higher if you consider the 13+ billion years the Milky Way has been around. We have a tendency to only look at life in its present context. If we consider the 9+ billion years before our solar system even existed, the odds of life forming increase significantly.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted