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Methane is not nearly as good a signal to look for life as larger organic molecules are. Methane can easily be created by abiotic processes and remain stable wh
by opportune 7y ago
Methane is not nearly as good a signal to look for life as larger organic molecules are. Methane can easily be created by abiotic processes and remain stable when not directly exposed to radiation or oxidizers indefinitely: this happens on earth, and we do have oxidizers everywhere. Larger organic molecules are less likely to have abiotic origins by any known process and are almost always much less stable.
On earth you can test whether methane has organic or abiotic origins by testing its isotopes. We can do this because we understand decently well how the geologic past of earth unfolded. We could probably do a similar thing for mars
>The Earth is 4.5 billion years old. And the universe, at least based on estimates from the Big Bang, is something like fourteen billion years. So, if life evolved somewhere else, that buys you about ten billion years of time.
Obviously I'm no expert, but you have to keep in mind, it took a decent amount of time for non-violent stars to become the norm / stellar neighborhoods to calm down and for overall metallicity to become significant enough to allow for the formation of terrestrial planets.
- sandworm101 7y ago>> and for overall metallicity to become significant enough to allow for the formation of terrestrial planets. You don't need much metallicity before terrestrial planets start forming. They would certainly be rarer in the early universe, but stars filter material very quickly (pushing light stuff further away, stripping new planets to their dense cores). So even with 10% of today's metallicity, there would still be plenty of terrestrial planets. (lol. My spellcheck corrects "metallicity" to "Metallica".)
- irrational 7y agoSo even with 10% of today's Metallica, there would still be plenty of terrestrial planets.
- ivolimmen 7y agoUsername checks out
- tlb 7y agoCarbon dating depends on the details of the biosphere. C14 is produced in the upper atmosphere by cosmic rays, and then (once it's fixed into a tree) it decays with a half-life of 5700 years. So if a chair is made of wood with a C14 fraction that's 1/4 of the atmospheric fraction, you can say it's 11400 years old (as a first-order approximation -- the actual science calibrates out a lot of things.) But it's not clear that the presence of life would affect the C14 ratio in the upper atmosphere. The fraction should be where the production rate (proportional to the cosmic ray flux and percentage of nitrogen) matches the decay rate (1/5700 / year)
- opportune 7y agoBut Mars also has an atmosphere (although thin) of CO2 exposed to cosmic rays, no? So we could determine if there is some sort of CO2->methane cycle by seeing if there is any appreciable amount of C14 in the methane we find on Mars? Apologies if that's a stupid question, I'm out of my element here
- tlb 7y agoC14 is actually produced from cosmic rays hitting nitrogen, not carbon. The impact turns a proton into a neutron. Both CO2 and CH4, once the chemical bond is made, only decrease in C14 fraction as it spontaneously decays. Astronomers are pretty good at deducing things from the few, imprecise measurements they can make from millions of miles away, so you should never rule out them being able to figure out something. But it'll depend on a lot of assumptions.
- emmelaich 7y ago> I'm out of my element here Nice
- keyle 7y agoPardon my ignorance, but the Earth is 1/3 the age of the Universe?
- tmoravec 7y agoAs far as our current understanding goes, yes. But it looked very different in the first billion years.
- marcosdumay 7y agoAbout that. The first stars appeared very early, and lasted for a very short time, so this may be a huge timespan.
- rjurney 7y agoThey would have produced metals pretty quickly given that most of them would be massive and emit stellar wind and/or supernova?
- marcosdumay 7y agoThat's what I understand, but I'm not an astronomer.
- saalweachter 7y agoYes, but it is projected to last for < ~0.1% of the overall lifespan.
- flukus 7y agoYep, time is the universes only dimension the earth is not a tiny and insignificant blip on, so far anyway.
- keyle 7y agoYeah this exactly. Today my perspective of the universe changed a little.
- EGreg 7y agoDude. How do people know how big or old the universe is? That’s just the VISIBLE universe. I bet they will change their estimates in 100 years again
- holler 7y agoThere's a great Imax film called Dark Universe were Neil deGrasse Tyson explains how it's likely that if an observer in the vicinity of Earth were to travel to the furthest point in space that we can observe, they would see the exact same thing in all directions that we see from Earth. They would see beyond our Earthly visible region of the universe and see more universe beyond it. If the observer travelled further again, they would again see the same thing in all directions. Basically we can only see so far, but it's likely no matter how far you travel in the universe, you'd just see more expansive universe in all directions. None of this is proven of course but it's an interesting and plausible idea.
- drran 7y agoIt possible that we will see much denser region of Universe in one direction at some point, while we will see less dense regions until clean vacuum in other directions. It's hard to predict which outcome is more plausible at this point of science research. My own research predicts that Universe has ceiling for black hole size, which means that first variant is much more likely than second.
- ivalm 7y agoAssuming the universe is homogeneous (ie we are not in some special place) you only need to see a small portion of the universe to date it. https://en.m.wikipedia.org/wiki/Age_of_the_universe https://en.m.wikipedia.org/wiki/Age_of_the_universe
- 2a96eb7d685a49c 7y agoFrom what I understand the abiotic ways that methane can be produced involve geologic or seismic activity which is not something that we have observed on Mars. Also, I thought the thin atmosphere on Mars meant that methane does not remain stable there.