There seems to be a bit of optimism that we may be finding the existence of extra-terrestrial life relatively soon, especially on places like Mars or Europa but I think that if we find life on one of these places and it’s based on DNA it’s nowhere near as exciting as finding life that is not based on DNA.
If we find DNA-based life on Mars it means that that it almost definitely shared a common ancestor with life on Earth at some stage and either life started on Earth and was transferred to Mars or vice-versa. This means that life only started once as far as we know and while this is interesting it doesn’t really change much in the big scheme of things.
If, however, we find a completely different form of life on Mars then is would show that life has started independently as least twice and so the odds of life being somewhere else in the Universe are now much higher and this is a LOT more exciting.
I think it’s likely that life contamination can spread, and I think it would be cool to confirm that or to find a different kind of life. I would be more exciting about finding life on Mars, Europa, etc., than any disappointment re: its origin, unless it was recent contamination by our space probes or something.
It might even be exciting to find decades-old contamination, if it’s been able to mutate enough to be a wildly divergent strain. If we could bring it back we might be able to learn how to engineer organisms to better survive if we ever try to colonize!
I don’t think it would be a disappointment – rather it would prove that panspermia is possible. And if panspermia is possible between worlds in the same solar system, it might just be possible between solar systems (over millions and billions of years), which greatly increases the likelihood of life in other star systems.
So life may have only “arisen” once in the galaxy (or even the universe), but if it can travel through space, how likely is it that Earth (or Mars) was the originator, rather than a stop on a long, long journey?
Finding life anywhere other than within ~100 miles of earth’s surface would be a universe-changing event.
I think both the genpop and the science/fiction crowds have gotten very blase about life elsewhere and tend to forget we have yet to find any trace of it.
This is where I disagree with you. If we find life on Mars and we find out that it is similar to life on Earth it probably means that one of these planets probably seeded the other and while this is interesting and exciting in my mind it does nothing to show that life has originated elsewhere in the universe. If we can find some conclusive evidence of life that originated completely separately from Earth life I would find this amazing and because this now means that the chance that life exists all over the universe is now so much more probable.
At the moment I feel quite pessimistic about intelligent extra-terrestrial life mainly because if it is out there, why haven’t we seen anything yet? Maybe there is plenty of life just none of it is intelligent. As far as I can see nothing says that life needs to evolve intelligence, after all the dinosaurs did fine for over a hundred million years without much intelligence.
I think it more likely we’ll simply identify life - either present or fossilized - quite some time before we determine if it is DNA based or not. The robots we have on Mars right now aren’t capable of making that sort of analysis, we’d have to send either something a lot more specific/sophisticated, something that can send useful samples back to Earth for analysis, and/or actual people to do that sort of work.
I think that’s quite a leap. We don’t know how life got started in the universe, we don’t know if DNA could evolve more than once, or if there are systems that are DNA based but arose independently.
So, yes, DNA (or RNA, which is another possibility) could indicate common origin but at this point it’s not certain that it would.
I’m sorry, but this does not follow. There are plenty of examples of parallel and convergent evolution on Earth. Nucleic acids are even given as an example of the latter in Wiki.
I think that if DNA-based life is found the skeptics will insist it’s contamination no matter how stringent our precautions were and no matter how different that Mars life is in other details. As well the religious will use this similarity to insist it’s all still god’s plan and we’re still the center of the Universe and la la la I’m not listening to you Mr. Scientist.
Better to find something totally different.
OTOH if we find dead remains (fossil or otherwise) that aren’t DNA-based, then proving that it was once alive versus just being a mineral / crystal formation will be difficult.
Only if we find something unequivocally alive, reproducing and doing some analog to respirating regardless of the chemical specifics, can we really know for sure the thing is properly “life.” It being non-DNA/RNA based would be gravy at that point.
It’s not guaranteed that we will even recognize non-DNA based life when we see it. Think about it. A life form based on silicon crystals could well appear to us as a mildly curious quartz formation.
Finding alien DNA based life would be very exciting, because it would be something with a grain of commonality.
As I understand it, silicon is not actually a useful base for life as it tends to form simple chains, rather than the complex structures carbon forms. Further, Si-Si bonds are much weaker than C-C bonds. I’ll also note that we have yet to detect complex silicon molecules in space, whereas we have detected complex carbon molecules. And you better have lots of fluorine around to recycle the SiO2 you’re excreting.
DNA-based life on Mars would be plenty exciting. However, there are a range of possibilities, which could be resolved by sequencing the DNA. Off the top of my head, here are some possibilities from least to most interesting:
The martian DNA sequence closely matches something that exists on earth today. That implies mere contamination carried by a lander.
The DNA sequence appears to have a common ancestor with something that exists on earth. That implies a relatively simple one-way panspermia scenario, where some bit of ejecta from Earth happened to carry an organism that then survived and thrived on Mars. That’d be interesting enough to keep a few scientists busy for their entire career.
The DNA includes multiple sequences with different common ancestors on Earth. An expansion of scenario 2, but demonstrating frequent and sustained colonization of Mars by something from Earth.
The DNA has sequences that appear ancestral to some DNA sequences on Earth. This gets more exciting, since it implies frequent DNA and horizontal gene transfer between Mars and Earth. Now, the entire genomics field has a small revolution, while they find evidence of Martian genes transferred to different species on earth throughout evolutionary history.
The DNA is clearly related to the earliest known life on Earth. Resolving whether the common origin is on Earth, Mars, or somewhere else will require a lot more data. We’ll probably see a wave of new probes sent out to catalog different sorts of life on Mars and elsewhere in the solar system to find the ultimate origin.
The DNA is unlike anything we have seen on earth (e.g. different bases, or the same bases but no ribosome). This possibility will be the most profound, as evidence for a second independent origin of life. However, nothing much would change for biologists studying life on Earth – we’d still focus on the same thing we do now, without needing to consider how alien biology works.
Maybe. it certainly would raise the possibility of contamination. It is looking like Mars won’t have any life, except underground or in hot springs-the surface is sterilized by UV radiation. But if we found fossil life-that would be very interesting.
Well, you’re free to, and I understand the real gist of the question is whether we ever discover life that can’t possibly be contamination from Earth, via human activities or asteroid-splattering.
But since we have zero, zip, nada, nuttin’, nowayhozay, cube root of f*ck-all evidence of life anywhere outside our stratosphere… ANY discovery of life elsewhere would be an exciting event. I think that even DNA-based life found on Luna or Mars, where it could be contamination, would be an epochal event if it couldn’t be matched to existing earth species.
A 3rd possibility is both were seeded together either from a common source or DNA based life is just a common occurrence that it just happens.
DNA life would seemingly be easier to find because we know it and we know where it already lives and thrives. This does not preclude other forms of life. There may be living being inside the sun, but they are just too different for us to even begin to know they are life.
So yes finding another form of life would be wonderful, but finding DNA life is too. We may need to find DNA life in a vastly different environment first to understand more of what life is.
Finding life >>> not ever finding life. That’s a given.
The question is would it be cooler to find DNA-based life or non-DNA based life? I tend to agree that it would be cooler to find completely novel life, based on completely novel chemistry. That would really strengthen the argument that life isn’t a wildly improbable development, but is perhaps a common, maybe even nearly inevitable outcome of any complex chemical system. That would be the most exciting universe to live in.
The chances against as complex and specific a molecule as DNA arising twice in two planets next to each other without a common origin can be safely stated as zero. It’s not just improbable, it’s macroscopic-quantum-underwear-removal improbable.
Since we don’t know how DNA or RNA came about I don’t see how you can definitively say that. We only have one example of a world with life, it’s a little hard to predict these things based on just one example.