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Life actually is pretty common I think. The simplest definition of life would be molecules that replicate. An example of an arguably form of life in space can b

Life actually is pretty common I think. The simplest definition of life would be molecules that replicate. An example of an arguably form of life in space can be found at http://www.sciencedaily.com/releases/2007/08/070814150630.htm http://www.sciencedaily.com/releases/2007/08/070814150630.ht... When you look at the way evolution works, it becomes clear that there is life elsewhere. Let's take a set of atoms. When they're bombarded with energy they react with each other and form compounds. While predictable, there is a slight amount of randomness in this. Eventually, one of these will be able to replicate itself. A simple example is a structure that would interact with other molecules to help them react to produce a duplicate. This is a biological enzyme. The current hypothesis is that early life was just RNA. RNA is a carrier of genetic information, but also can be an enzyme. Common examples are ribosomes, which read the genetic code and make all our proteins from that code, and self-splicing introns. This early RNA was probably able to produce copies of itself. This is life. We see certain molecules important for life, such as a sugar molecule, as being meaningful and special. However, as far as nature is concerned it's not. Take a deck of cards. If you were to shuffle them up, they appear disordered, but that's only because we don't give that particular order a meaning. It's just as probable to get that particular order as it is to get them Ace, king, queen, jack, etc. So basically, life will eventually happen given a long enough period of time. It's inevitable. Life flourished on Earth. Given another very similar system, it's highly probable life was also present there at some point.

jey 19y ago
I agree, given enough planets and enough time, we can reasonably expect to find some other life-like system. Given a sample size of 1 planet (Mars), it seems like wishful thinking, unless you think that life is very likely to develop on any planet that is Mars-like. So if you say "I think 90% of Mars-like planets will develop life", then it makes sense. Hell, even if you only give it a 2% chance, we could poke around some. But I bet even if we assume that Mars and Earth have had similar conditions, it would take many thousands of Earth-like planets (at least) before we find another instance of a life-like system, even optimistically.
- ingenium 19y ago
  Yes, but it has been shown that Earth and Mars have been impacted by comets or meteors, and ejected matter into space which then hit the other planet. Life, or at least molecules that are precursors to life, could easily have hopped a ride on these. If it happened later, say after bacteria had evolved, then bacterial spores could have been transported as well. Those things are really hard to destroy. As for a planet that is Earth-like (or Mars-like when Mars was similar to Earth), I think it is a 98% chance or higher. I'd be willing to bet that if life was wiped out on Earth, it would occur again in a billion years or so. It just seems like matter in general has the tendency to organize and behave in a way that favors life. It does things randomly, but once something happens that can kind of reproduce, it stays around. A bunch of these accumulate until it starts to resemble a cell. Many chemical reactions in life would happen on their own in enough time. We use enzymes to make this happen faster. Early life takes a long time to evolve up because it doesn't have these enzymes, so it has to wait for the reaction to just happen. Consciousness, or what we consider consciousness, is perhaps another story.
  - jey 19y ago
    "As for a planet that is Earth-like (or Mars-like when Mars was similar to Earth), I think it is a 98% chance or higher." I suppose this is where we disagree. I put it at well under 1%, even if we were to assume that the panspermia hypothesis is true. On the other hand, assuming panspermia, there's enough of a chance for life to be on Mars given the fact that its neighbor has life. Finding life on Mars could also lend support to the panspermia hypothesis.
    - Retric 19y ago
      The earth is around 4.5 billion years old. Life showed up within the first 1/2 billion years right around the time it cooled off enough for life to be possible. But let's say it's 50 / 50 every 500 million years (I think it's a lot higher than that.) well that's 99.8% after 4.5 billion years. Note: If that seems high it's about the same as 1 chance in 1000 per million years for any form of life to show up.

jey 19y ago

I agree, given enough planets and enough time, we can reasonably expect to find some other life-like system. Given a sample size of 1 planet (Mars), it seems like wishful thinking, unless you think that life is very likely to develop on any planet that is Mars-like. So if you say "I think 90% of Mars-like planets will develop life", then it makes sense. Hell, even if you only give it a 2% chance, we could poke around some. But I bet even if we assume that Mars and Earth have had similar conditions, it would take many thousands of Earth-like planets (at least) before we find another instance of a life-like system, even optimistically.

ingenium 19y ago
Yes, but it has been shown that Earth and Mars have been impacted by comets or meteors, and ejected matter into space which then hit the other planet. Life, or at least molecules that are precursors to life, could easily have hopped a ride on these. If it happened later, say after bacteria had evolved, then bacterial spores could have been transported as well. Those things are really hard to destroy. As for a planet that is Earth-like (or Mars-like when Mars was similar to Earth), I think it is a 98% chance or higher. I'd be willing to bet that if life was wiped out on Earth, it would occur again in a billion years or so. It just seems like matter in general has the tendency to organize and behave in a way that favors life. It does things randomly, but once something happens that can kind of reproduce, it stays around. A bunch of these accumulate until it starts to resemble a cell. Many chemical reactions in life would happen on their own in enough time. We use enzymes to make this happen faster. Early life takes a long time to evolve up because it doesn't have these enzymes, so it has to wait for the reaction to just happen. Consciousness, or what we consider consciousness, is perhaps another story.
- jey 19y ago
  "As for a planet that is Earth-like (or Mars-like when Mars was similar to Earth), I think it is a 98% chance or higher." I suppose this is where we disagree. I put it at well under 1%, even if we were to assume that the panspermia hypothesis is true. On the other hand, assuming panspermia, there's enough of a chance for life to be on Mars given the fact that its neighbor has life. Finding life on Mars could also lend support to the panspermia hypothesis.
  - Retric 19y ago
    The earth is around 4.5 billion years old. Life showed up within the first 1/2 billion years right around the time it cooled off enough for life to be possible. But let's say it's 50 / 50 every 500 million years (I think it's a lot higher than that.) well that's 99.8% after 4.5 billion years. Note: If that seems high it's about the same as 1 chance in 1000 per million years for any form of life to show up.