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

Life on other planets; are we looking at the wrong planets ?

  1. Aug 5, 2017 #1
    Scientists are looking for earth like planets/bodies to find life on other planets/bodies, somewhere that is warm enough that liquid water can exist, and somewhere with basic organic molecules. Here's where I have a concern, in the 4 billion years of earths life, to our knowledge life had only emerged once(about 3.5 billion years ago). Since earth itself is the most earth like thing(obviously) how is it that we have not found life that had a different emergence. Does the earth maybe not have the best conditions for new life to emerge? I just think there should have been more then 1 root to all the living things that exist, or has existed, given that we believe earth has the prime condition for life. Maybe we're wrong about what is needed to create life?
     
  2. jcsd
  3. Aug 6, 2017 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    I'll see if there is a forum that fits better than astronomy.
    Established life could have out-competed every new approach of life. It is possible that life could have developed multiple times but existing life was simply better adapted already. The first cells were probably slow, fragile, and not very flexible. Current life would simply eat something like that if it has anything of nutritional value.
    It is also possible that the emergence of life is extremely unlikely, happening on average just once per 10whatever habitable planets.
    A sample size of 1 for Earth might sound small, but outside Earth our sample size is even smaller (0). There is no indication that different conditions would be more favorable for life.
     
  4. Aug 6, 2017 #3

    jim mcnamara

    User Avatar

    Staff: Mentor

    Thread moved to Biology.
     
  5. Aug 6, 2017 #4

    jim mcnamara

    User Avatar

    Staff: Mentor

    Quick points:
    1. your statement is a good one in most ways, but it would have been improved with a little searching on the internet, so you would have seen #2.
    2. Exobiologists are very aware of this problem. The issue is that you cannot establish that hypothesis without data.
    3. There are life forms on Earth that have very different biosynthetic pathways - like methanogenic bacteria.
    https://en.wikipedia.org/wiki/Methanogen -- no "potty humor" please.
     
    Last edited: Aug 6, 2017
  6. Aug 6, 2017 #5

    Ygggdrasil

    User Avatar
    Science Advisor

    The fact that there all extant life derives from a single origin of life does not necessarily mean that there was only one independent origin of life. As others have mentioned, these different forms of life would have been in competition and maybe the common ancestor of all extant life out-competed all other forms from different origins of life (after all, it is estimated that over 99.9% of species that have ever existed on earth are extinct). Mathematical arguments have been made that it is likely that there were multiple independent origins of life on Earth, though no experimental or observational evidence of these independent origins exist. The fact that life arose on Earth relatively soon after conditions on Earth became amenable to life would also suggest that abiogenesis is not a very rare event.

    In terms of astrobiology, one of the advantages of looking for Earth-like planets is that we have some idea of what life on Earth-like planets should look like and what signs we should be looking for. For very different forms of life, it is unclear how we might go about looking for signs of these life-forms with unknown biochemistry.
     
  7. Aug 6, 2017 #6

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Much later and we wouldn't be around to discuss this question. Complex life will struggle within a billion years, assuming no large-scale artificial terraforming.

    Another thing to keep in mind: The history is not "a cell formed, and then all its descendants formed the different species". The last universal common ancestor (LUCA) lived long after the first cell. It had the full RNA to protein transcription mechanism already, and probably DNA as well. This LUCA was so successful that its descendants replaced everything that had evolved in parallel.

    Horizontal gene transfer can make this a bit more complicated, but let's ignore it here.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Life on other planets; are we looking at the wrong planets ?
Loading...