An interesting phenomenon I rarely see brought up in support of panspermia is the apparent universality of the genetic code. The fact that all known life shares a common genetic structure implies a common ancestor. The lack of competing genetic codes could be interpreted to imply that life only started on earth once, or that it only made it to earth once. Natural selection is a constant force, presumably new genetic codes could offer an advantage, e.g., robustness against damaging mutation, resulting in multiple competing genetic codes.
The notion of abiogenesis occurring only once on earth seems improbable considering complex organs like eyes have evolved independently several different times. Or the fact that convergent evolution "reinvents" similar species in response to similar selective pressures. Selective pressures constantly "push" life in the same directions, so it would seem that whatever forces gave rise to life would have happened so repeatedly, but there doesn't seem to be any evidence for that.
A clean explanation for this would be that life didn't start on earth, and earth may have never had the right conditions to originate life, hence no competing genetic codes. But it was still hospitable enough to maintain life, so one universal genetic code flourishes with no emergent competition.
Doesn't that just beg the question? If life originated on some other planet and made it to Earth, why did only the DNA-based lifeform(s) make it here?
If we assume that different kinds of life based on different nucleic acids can co-exist, then it seems unlikely that a single kind would have happened to be carried to Earth by a natural process.
If we assume DNA has some inherent fitness advantage (so that only DNA-based life survived the journey), than we don't need the additional assumption of panspermia: perhaps only the DNA-based life survived some early period in Earth's history.
Also, for abiogenesis, given that we still can't reliably reproduce something like that, and that we have never seen new kinds of life spontaneously appearing on Earth, we do have some circumstantial evidence for the possibility that it is an incredibly unlikely event, such that it might have only happened once in Earth's history.
Edit: There is also another simple possibility: perhaps given the resources available on Earth, either forever or in the period where abiogenesis was possible, perhaps DNA(+RNA) is the only molecule with the right properties to act as genetic material. Perhaps there is no common ancestor to all life on Earth, but a "forest" of inter-breeding, spotnaneously arisen original organisms, but they were all DNA/RNA-based simply because of the available resources.
On the contrary. If life started multiple times on earth competitive exclusion probably took care of all other primitive forms rapidly. Even small differences, energy efficiency and reproduction lead to situation where only one form of primitive life survives.
Once the life really started going, it changed the chemistry of the earth rapidly. Similar chemical evolution starting from scratch was not possible once the life started.
Eventually when photosynthesis started, biologically induced molecular oxygen caused so called Oxygen Catastrophe where Earth's chemistry turned from reducing into oxidizing. Oxygen also changed the chemistry in the seas and rocks. Molecular oxygen is great disinfectant.
> The fact that all known life shares a common genetic structure implies a common ancestor. The lack of competing genetic codes could be interpreted to imply that life only started on earth once, or that it only made it to earth once.
The more I read about DNA and RNA, the more it seems to me they're somewhat fundamentally grounded in chemistry - you can't just make codons mean arbitrary things by messing with the replication mechanisms. There's less path dependence, and more of "one optimal way of doing things".
That said, I think it's reasonable to assume we all have common lineage[0] - it's arguably a winner-takes-all scenario, as there's a huge first-mover advantage for the first self-replicating family of things that got loose on the world.
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[0] - causally, not genetically; the history of life is not a tree structure due to constant lateral gene transfer that bacteria and archaea engage in.
You can't quantify the complexity of something like an eye. The eye could actually be very very simple to form, due to circumstances and variables outside of our knowledge.
Scientists have discovered that the animal with the most genes--about 31,000--is the near-microscopic freshwater crustacean Daphnia pulex, or water flea. By comparison, humans have about 23,000 genes.
One of the most astonishing features of the D. pulex genome is its compactness: despite being around 200 Mb in size (around 16-fold smaller than the human genome which is 3,200 Mb in size); its 12 chromosomes contain a minimum set of 30,907 predicted protein-coding genes, more than the 20,000–25,000 contained in the human counterpart.
The unexpected complexity of the water flea genome compared with a human genome illustrates unknown dimensions of complexity that we cannot fully comprehend.
What this means is this. You do not know how complicated the original template of life is... the complexity for the first genome to produce instructions that allow for self replication to kick off evolution may be so complex that it could only happen once on our planet, once in this galaxy or once in the universe.
We simply do not have the knowledge to know the probability space of life on earth or life as we know it.
The genetic code isn't quite as universal as you might think. Here's an interesting article on the peculiarities of encoding in the mitochrondial genome, and what it tells us about evolution. https://whyevolutionistrue.wordpress.com/2014/09/28/guest-po...
OK, I'm not any kind of expert in this area, but is RNA not considered an early form of genetic coding? And DNA evolved from it? Also, don't viruses replicate by "borrowing" the mechanism of their hosts?
My understanding is that life visible to the naked eye is a minority of life forms on the planet. Maybe other forms of genetic coding than DNA are more prevalent than we anthropocentrists think.
> The notion of abiogenesis occurring only once on earth seems improbable considering complex organs like eyes have evolved independently several different times.
Evolution of eyes and abiogenesis aren't obviously similar enough for this analogy to be compelling without some narrative as to why what occurred with one should shape expectations of the other. The conditions in which life first emerged in either the Hadean or Eoarchean eons weren't around for much more of the history of the Earth; if the average expected frequency of abiogenesis under the conditions it actually emerged was once every quarter billion years or so, then—no matter which point in the possible range of time it first occurred—conditions wouldn't have been right for more than one to a very few instances, and if there were more than one, still one would likely be much more established by time available to spread alone, and then there were be massive environmental changes likely producing extinctions. Only one lineage surviving that bottleneck isn't surprising even if there were more before, and while we have evidence of early life it's far from complete either in coverage or ability to determine biochemistry and lineage.
It's really not necessary to invoke extraterrestrial origin to explain only one lineage on Earth (and it actually may make the problem worse: because then you have to explain why we haven't gotten alternate lineages from the same or other extraplanetary sources.)
Why are there no other human species (anymore)? Because there was no room for them anymore and they could not compete. In the same way, it it very well possible that life utilizing other genetic code got stamped out (early on).
The panspermania hypothesis has one very large hurdle to get over: the half-life of DNA is ~500 years [0].
If life came from outside our planet via an asteroid or something, then it had to be a LOT of DNA that came over. More exotic theories can be concieved, but the jist is that it is really really hard for DNA to travel the stars and between planets intact.
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.
Carbon 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)
>> 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".)
Even though we have only one datapoint, I wonder how much can be inferred from this planet's life characteristics.
First, life came about rather shortly after the planet was able to sustain it. So this timing is either very unlikely, or biogenesis has a high probability of happening, or the initial life got seeded from off planet (from a very rare initial phenomenon).
Second, all the biosignatures from all forms of life are similar. For example, corality (left handed versus right handed molecules) is the same in all life examples we had. So that means that biogenesis happened only once. Otherwise we would have multiple unrelated examples (yes, there is the possibility that one form "ate everything else", but we have all kinds of variety instead of only one organism becoming dominate). So if biogenesis happened only once (for all of our bio examples), then it is either a rare event that just happened to occur very shortly after the planet cooled, or it happened sometime before Earth was hospitable for life and elsewhere in the universe.
Does any of this make sense? Or am I reading too much into the tea leaves?
The question of where life originated will have no good answer until we figure out how to create life from basic components. We still don't know how to do that yet.
Yes, Urey and Miller showed that you could get simple organic molecules by passing an electric charge through gasses thought to be present around the early Earth.
But going from low molecular weight inputs to life is a vastly different problem. You could think of it as the most complicated bootstrapping problem in the universe.
Nobody has managed to do it in the lab, either. What can't be built from scratch can't be understood very well, and therein lies the problem.
If we had a stepwise procedure for building a self-replicating, self-feeding organism of any level of complexity from base components, we would know exactly what to look for.
Until then, the idea of sending a DNA amplifier to Mars isn't a bad fallback position.
There has been progress within the theory of non equilibrium thermodynamics which hint that local entropy decrease is baked into the physics. That is to say life just kind of falls out of the physics of thermodynamic systems of a certain type. That certain type being anything that dissipates a source of energy. Personally I think abiogenesis is relatively easy and there is large scale panspermia going on. The universe is like a yoghurt, bacteria everywhere and novel abiogenic origins occurring all over the place, although there are probably dominant kinds of life. DNA based being one.
If we succeed, it would be the most important breakthrough in the history of humanity, and would have very deep existential implications. It wouldn't definitely rule out a supreme being as the creator of the universe we live in, but it would make the gap between us and that being much smaller than millions of people on earth believe now.
Um. That's been done? In several ways? Replacing parts of existing life with different elements (arsenic?). Hand-crafting a genetic code from parts of existing creatures, to create entirely new and different creatures. There's even a company in the town next to me (IDT) that delivers to-order DNA samples via fedex anywhere in the world.
> The reason this news registered among scientists is that methane is often a sign of life; although the gas can be produced by various chemical reactions, most of it comes from animate beings.
This doesn't sound right at all. There are literally lakes of methane on Titan. The atmospheres of Jupiter, Saturn, Uranus, and Neptune all contain significant methane--it's what makes Uranus and Neptune blue. Pluto has methane ice.
IIRC from the original reporting, some recent research suggested that there's more methane than contemporary geological models of Mars predict. Which likely says more about the [non-biological] deficiencies in those models than it does the likelihood of life.
I'm not an astro-anything, so feel free to correct me. But it's telling that the interviewee never comes close to confirming the reporter's claims; they're simply quoted as saying, "I think probably many people would like the idea of methanogens on Mars", and "the idea that they might be related to methanogens on Earth is not crazy." Isaac Chotiner is a name I'll try to remember so I can avoid his articles.
There is ancient methane in those places. But something on Mars is producing methane.
Methane breaks down pretty fast in Mars' atmosphere, and yet it reappears there occasionally. That can certainly have non life explanations. But they're fairly exotic.
IIRC, methane should not persist on Mars, and theres not been a global phenomenon detected that can explain its occasional detection. Therefore, transient detections are considered indicators of possible life, since nothing else seems to explain it.
It's not that it's rare everywhere, it's that it's rare on Mars.
The author (Chotiner) has indeed made a mis-statement about the state of knowledge on planetary CH4, but that doesn't pertain directly to most of the article's content, which is about DNA/RNA.
As you point out, the state of Mars CH4 is quite complex and extremely controversial, with 3 different measurements (Curiosity + 2 orbiters), low concentrations observed (~10 ppb) and multiple physical processes going on. Here's a pretty good recent summary:
Minor fun fact: Fred Hoyle, possibly the most public proponent of Panspermia in the last few decades, also coined the phrase "Big Bang theory" to dismiss an alternative to his preferred Steady State theory of the universe.
Sometime champion of arch positions, he was once quoted as saying "it is better to be interesting and wrong than boring and right".
It is a pretty out there theory, but at one point the universe would have cooled enough from the very hot big bang origins to allow liquid water to exist everywhere, but not cooled sufficiently to cause everything to freeze.
If any rocky planets existed at the time, maybe that was the origin of life which was much more able to spread widely due to the small size of the early universe.
I suspect that a formal, anonymous survey of astrobiologists would find that the idea is far more prevalent among experts than Ruvkin's estimate that "one per cent would buy into the idea of life spreading the way I’m sort of promoting it".
It's just risky to express, for cultural reasons, until there's tangible proof. Many scientists are temperamentally reluctant to speculate without conclusive evidence, especially given the penchant of the press to sensationalize any such theories. It'd raise difficult questions about our place in the universe, and possibly popular fears.
Thinking science had already settled on a consensus that simple life is everywhere might even paradoxically reduce funding for new missions to test the idea. After all, there have been tantalizing hints of life-processes on Mars going back to the Viking lander experiments of the 1970s – and yet we still can't seem to send a lab package that'd definitively answer the question! But the hope of figuring it out motivates new missions.
There was this interesting article posted here some time ago that plotted the complexity of life found on earth vs time, and by using the right methodology and logarithmic scales, it arrived at a nice linear line over many data points and several billions of years. And the line converged to a 0 point, but that point was a few billion years before earth was created 4.5 billion years ago, adding more credibility to a panspermia theory. Can anybody remember that article and its url?
I have wondered if panspermia could have occurred in the Sun's birth cluster. This cluster would have had a very high density of stars, with gas around them to slow and capture material ejected from their neighbor systems. And the asteroids in orbit around these stars would have still be warm enough to have liquid water in them, so life could potentially have been seeded in a wide variety of environments.
This possibility, if true, means SETI might be worthwhile even if the actual origin of life is astronomically rare, much less than once per observable volume of the universe. SETI would look at the other stars that were in that cluster. Even if the rest of the universe were devoid of life, they (like the continents of Earth, or planets in our solar system) could share the same origin event.
This scenario might also explain why life apparently originated so early in the history of our solar system: this sort of natal panspermia would statistically amplify origin-of-life events that happened early on, by multiplying the number of systems they'd affect. This amplification would occur even if OoL was extremely rare.
Based on nothing but faith and an irreducible cynicism, my money says we end up going full circle, from "Earth is alone in the universe in regards to life" to "Life is a fungus, found anywhere the most basic of conditions are met" (at least over periods of millions of years at stellar scales)
People forget that this discussion is not necessarily related to life. When various European explorers went out, in many cases they didn't know what to expect. When they met strange peoples, most of them refused to believe these were actually human.
It takes a good long while for humans to recognize other lifeforms like us. We naturally think that we're unique, that wherever we call home is special and the center of things. Combine that with galactic distances and it might be a good while before we realize that the universe is actually full of aliens that look just like humans only with bumpy heads (Obligatory Star Trek joke)
Maybe we could test this someday with petri dishes in orbit. Outfit satellites with catch basins that funnel into various potentially habitable pods and see what grows. Park them in a lagrange point for better isolation.
But if panspermia is true such critters in the cosmic wind would be cousins of life on earth, and it would be difficult (impossible?) to distinguish an alien microbe from domestic contamination. If it's false we see nothing, and wonder if it's because space is sterile or we're just not yet offering it the right primeval soup.
My biology knowledge is admittedly weak, but a question for those who might know: a lot of the discussion here is about how we only know of "life" based on nucleic acids (DNA). However, prions seem to replicate themselves without the help of nucleic acids. Could this in some way be seen as a competing form of "life"?
It always seemed to me that the biggest argument against panspermia is the relative hostility to "life" of space versus a planet like Earth. The heliosphere protects the solar system from a significant amount of interstellar cosmic rays and x-rays, Earth's magnetosphere offers additional protection, and our atmosphere, particularly the ozone layer, offers additional protection while also protecting against UV and high energy particles from the Sun. Ionizing radiation and short wavelength EM radiation are destructive to life and really the persistence of any large complex molecules. Combine that with the vacuum of space and temperatures barely above absolute zero and life originating via panspermia seems significantly less likely than originating natively on Earth.
I'd say the biggest argument against panspermia is that the organisms responsible for it need to be successful locally and universally, at the same time. Reproduction is expensive and intrastellar reproduction is incredibly low yield. So organisms would need to have evolved to both capture an entire ecosystem AND waste a bunch of energy blowing their seed into the solar system.
The idea just doesn't jibe with my understanding of evolution.
What if we began a 'seeding' experiment, suppose there could be more life but isn't because life doesn't spread well in the vacuum of space. What if we began sending bacteria and other micro-organisms to potentially habitable planets via tiny spacecrafts. If we were to seed as many planets as we could possibly find, then eventually (in a million years or so), this entire galaxy could be teaming with life and the fermi paradox will be refuted as there will be no way not to see the life that is out there. We may still not be able to traverse the stars by that time at least not without generation ships but our descendents could at least wave from afar and maybe communicate across vast distances with intelligent life that we today helped seed/create.
I'm not really on board with the idea of just blindly infecting all habitable planets with Earth life. We should look but don't touch until we have some clue what the heck we are doing and why.
What I find more interesting is the potential frequency with which new life from origins other than earth has been mixed together with what is here. A lot of stuff falls into our atmosphere and I doubt we know where all of it comes from.
I commented today on a bit of dermatological discussion where they claim our skin has a biome of bacteria. This is in addition to the gut biome that is starting to look like it contributes to a wide array of human health issues. Part of me wonders how much of those biomes (e.g. how many bacteria within that biome) are from sources outside our planet.
Well, if they did, then the fact that the basic DNA machinery is the same implies that we and the alien bacteria had a common ancestor somewhere back there.
I wish he had posited a theory for how life from Mars would have even gotten here. Some comments have said an asteroid hit Mars and then redirected to Earth with early life on it? Is that possible/likely?
Don't know if anyone has ever considered this (ignoring gross simplifications), but as depictions of aliens are typically conceptualized from creatures we see on earth. Is it possible that if we are the only living creatures that have (yet) gained heightened consciousness, then spreading the DNA of all life on earth across the universe in a similar fashion to how our microbial life arrived on earth is how we ensure that life truly goes on if we fail?
“...what if it started here and then spread elsewhere? And so we found some sort of DNA on Mars, but that’s because it spread there from Earth. Is that possible?
Yeah, but that sort of places us at the center of the universe, and all the force of history is to say, “Don’t think of us as the center. We’re nothing.””
What kind of argument is that? Sounds like some kind of anti-geocentric dogma, not an actual argument.
[+] [-] rectangletangle|6 years ago|reply
The notion of abiogenesis occurring only once on earth seems improbable considering complex organs like eyes have evolved independently several different times. Or the fact that convergent evolution "reinvents" similar species in response to similar selective pressures. Selective pressures constantly "push" life in the same directions, so it would seem that whatever forces gave rise to life would have happened so repeatedly, but there doesn't seem to be any evidence for that.
A clean explanation for this would be that life didn't start on earth, and earth may have never had the right conditions to originate life, hence no competing genetic codes. But it was still hospitable enough to maintain life, so one universal genetic code flourishes with no emergent competition.
[+] [-] tsimionescu|6 years ago|reply
If we assume that different kinds of life based on different nucleic acids can co-exist, then it seems unlikely that a single kind would have happened to be carried to Earth by a natural process.
If we assume DNA has some inherent fitness advantage (so that only DNA-based life survived the journey), than we don't need the additional assumption of panspermia: perhaps only the DNA-based life survived some early period in Earth's history.
Also, for abiogenesis, given that we still can't reliably reproduce something like that, and that we have never seen new kinds of life spontaneously appearing on Earth, we do have some circumstantial evidence for the possibility that it is an incredibly unlikely event, such that it might have only happened once in Earth's history.
Edit: There is also another simple possibility: perhaps given the resources available on Earth, either forever or in the period where abiogenesis was possible, perhaps DNA(+RNA) is the only molecule with the right properties to act as genetic material. Perhaps there is no common ancestor to all life on Earth, but a "forest" of inter-breeding, spotnaneously arisen original organisms, but they were all DNA/RNA-based simply because of the available resources.
[+] [-] nabla9|6 years ago|reply
Once the life really started going, it changed the chemistry of the earth rapidly. Similar chemical evolution starting from scratch was not possible once the life started. Eventually when photosynthesis started, biologically induced molecular oxygen caused so called Oxygen Catastrophe where Earth's chemistry turned from reducing into oxidizing. Oxygen also changed the chemistry in the seas and rocks. Molecular oxygen is great disinfectant.
[+] [-] TeMPOraL|6 years ago|reply
The more I read about DNA and RNA, the more it seems to me they're somewhat fundamentally grounded in chemistry - you can't just make codons mean arbitrary things by messing with the replication mechanisms. There's less path dependence, and more of "one optimal way of doing things".
That said, I think it's reasonable to assume we all have common lineage[0] - it's arguably a winner-takes-all scenario, as there's a huge first-mover advantage for the first self-replicating family of things that got loose on the world.
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[0] - causally, not genetically; the history of life is not a tree structure due to constant lateral gene transfer that bacteria and archaea engage in.
[+] [-] crimsonalucard|6 years ago|reply
Scientists have discovered that the animal with the most genes--about 31,000--is the near-microscopic freshwater crustacean Daphnia pulex, or water flea. By comparison, humans have about 23,000 genes.
One of the most astonishing features of the D. pulex genome is its compactness: despite being around 200 Mb in size (around 16-fold smaller than the human genome which is 3,200 Mb in size); its 12 chromosomes contain a minimum set of 30,907 predicted protein-coding genes, more than the 20,000–25,000 contained in the human counterpart.
The unexpected complexity of the water flea genome compared with a human genome illustrates unknown dimensions of complexity that we cannot fully comprehend.
What this means is this. You do not know how complicated the original template of life is... the complexity for the first genome to produce instructions that allow for self replication to kick off evolution may be so complex that it could only happen once on our planet, once in this galaxy or once in the universe.
We simply do not have the knowledge to know the probability space of life on earth or life as we know it.
[+] [-] Angostura|6 years ago|reply
[+] [-] hdfbdtbcdg|6 years ago|reply
[+] [-] kitd|6 years ago|reply
My understanding is that life visible to the naked eye is a minority of life forms on the planet. Maybe other forms of genetic coding than DNA are more prevalent than we anthropocentrists think.
[+] [-] dragonwriter|6 years ago|reply
Evolution of eyes and abiogenesis aren't obviously similar enough for this analogy to be compelling without some narrative as to why what occurred with one should shape expectations of the other. The conditions in which life first emerged in either the Hadean or Eoarchean eons weren't around for much more of the history of the Earth; if the average expected frequency of abiogenesis under the conditions it actually emerged was once every quarter billion years or so, then—no matter which point in the possible range of time it first occurred—conditions wouldn't have been right for more than one to a very few instances, and if there were more than one, still one would likely be much more established by time available to spread alone, and then there were be massive environmental changes likely producing extinctions. Only one lineage surviving that bottleneck isn't surprising even if there were more before, and while we have evidence of early life it's far from complete either in coverage or ability to determine biochemistry and lineage.
It's really not necessary to invoke extraterrestrial origin to explain only one lineage on Earth (and it actually may make the problem worse: because then you have to explain why we haven't gotten alternate lineages from the same or other extraplanetary sources.)
[+] [-] ivanhoe|6 years ago|reply
[+] [-] joycian|6 years ago|reply
[+] [-] Balgair|6 years ago|reply
If life came from outside our planet via an asteroid or something, then it had to be a LOT of DNA that came over. More exotic theories can be concieved, but the jist is that it is really really hard for DNA to travel the stars and between planets intact.
The simplier explination is that it started here.
[0] https://royalsocietypublishing.org/doi/full/10.1098/rspb.201...
[+] [-] opportune|6 years ago|reply
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.
[+] [-] tlb|6 years ago|reply
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)
[+] [-] sandworm101|6 years ago|reply
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".)
[+] [-] keyle|6 years ago|reply
[+] [-] 2a96eb7d685a49c|6 years ago|reply
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[+] [-] EGreg|6 years ago|reply
[+] [-] derekp7|6 years ago|reply
First, life came about rather shortly after the planet was able to sustain it. So this timing is either very unlikely, or biogenesis has a high probability of happening, or the initial life got seeded from off planet (from a very rare initial phenomenon).
Second, all the biosignatures from all forms of life are similar. For example, corality (left handed versus right handed molecules) is the same in all life examples we had. So that means that biogenesis happened only once. Otherwise we would have multiple unrelated examples (yes, there is the possibility that one form "ate everything else", but we have all kinds of variety instead of only one organism becoming dominate). So if biogenesis happened only once (for all of our bio examples), then it is either a rare event that just happened to occur very shortly after the planet cooled, or it happened sometime before Earth was hospitable for life and elsewhere in the universe.
Does any of this make sense? Or am I reading too much into the tea leaves?
[+] [-] apo|6 years ago|reply
Yes, Urey and Miller showed that you could get simple organic molecules by passing an electric charge through gasses thought to be present around the early Earth.
But going from low molecular weight inputs to life is a vastly different problem. You could think of it as the most complicated bootstrapping problem in the universe.
Nobody has managed to do it in the lab, either. What can't be built from scratch can't be understood very well, and therein lies the problem.
If we had a stepwise procedure for building a self-replicating, self-feeding organism of any level of complexity from base components, we would know exactly what to look for.
Until then, the idea of sending a DNA amplifier to Mars isn't a bad fallback position.
[+] [-] plutonorm|6 years ago|reply
[+] [-] dvfjsdhgfv|6 years ago|reply
[+] [-] JoeAltmaier|6 years ago|reply
[+] [-] wahern|6 years ago|reply
This doesn't sound right at all. There are literally lakes of methane on Titan. The atmospheres of Jupiter, Saturn, Uranus, and Neptune all contain significant methane--it's what makes Uranus and Neptune blue. Pluto has methane ice.
IIRC from the original reporting, some recent research suggested that there's more methane than contemporary geological models of Mars predict. Which likely says more about the [non-biological] deficiencies in those models than it does the likelihood of life.
I'm not an astro-anything, so feel free to correct me. But it's telling that the interviewee never comes close to confirming the reporter's claims; they're simply quoted as saying, "I think probably many people would like the idea of methanogens on Mars", and "the idea that they might be related to methanogens on Earth is not crazy." Isaac Chotiner is a name I'll try to remember so I can avoid his articles.
[+] [-] BurningFrog|6 years ago|reply
Methane breaks down pretty fast in Mars' atmosphere, and yet it reappears there occasionally. That can certainly have non life explanations. But they're fairly exotic.
[+] [-] jvanderbot|6 years ago|reply
It's not that it's rare everywhere, it's that it's rare on Mars.
[+] [-] mturmon|6 years ago|reply
As you point out, the state of Mars CH4 is quite complex and extremely controversial, with 3 different measurements (Curiosity + 2 orbiters), low concentrations observed (~10 ppb) and multiple physical processes going on. Here's a pretty good recent summary:
https://www.abc.net.au/news/science/2019-04-02/mars-express-...
The DNA-sensing instrument that's being prototyped is here: http://setg.mit.edu
[+] [-] mellosouls|6 years ago|reply
Sometime champion of arch positions, he was once quoted as saying "it is better to be interesting and wrong than boring and right".
https://en.m.wikipedia.org/wiki/Fred_Hoyle
[+] [-] throwaway2048|6 years ago|reply
If any rocky planets existed at the time, maybe that was the origin of life which was much more able to spread widely due to the small size of the early universe.
https://arxiv.org/abs/1312.0613
[+] [-] RachelF|6 years ago|reply
[+] [-] gojomo|6 years ago|reply
https://en.wikipedia.org/wiki/Panspermia
I suspect that a formal, anonymous survey of astrobiologists would find that the idea is far more prevalent among experts than Ruvkin's estimate that "one per cent would buy into the idea of life spreading the way I’m sort of promoting it".
It's just risky to express, for cultural reasons, until there's tangible proof. Many scientists are temperamentally reluctant to speculate without conclusive evidence, especially given the penchant of the press to sensationalize any such theories. It'd raise difficult questions about our place in the universe, and possibly popular fears.
Thinking science had already settled on a consensus that simple life is everywhere might even paradoxically reduce funding for new missions to test the idea. After all, there have been tantalizing hints of life-processes on Mars going back to the Viking lander experiments of the 1970s – and yet we still can't seem to send a lab package that'd definitively answer the question! But the hope of figuring it out motivates new missions.
(As should be clear, I'm strongly in Ruvkin's camp – and regularly comment to that effect here on HN: https://hn.algolia.com/?query=gojomo%20panspermia&sort=byDat... )
[+] [-] unknown|6 years ago|reply
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[+] [-] Darthy|6 years ago|reply
[+] [-] kleer001|6 years ago|reply
That's where I'd put my money.
[+] [-] pfdietz|6 years ago|reply
This possibility, if true, means SETI might be worthwhile even if the actual origin of life is astronomically rare, much less than once per observable volume of the universe. SETI would look at the other stars that were in that cluster. Even if the rest of the universe were devoid of life, they (like the continents of Earth, or planets in our solar system) could share the same origin event.
This scenario might also explain why life apparently originated so early in the history of our solar system: this sort of natal panspermia would statistically amplify origin-of-life events that happened early on, by multiplying the number of systems they'd affect. This amplification would occur even if OoL was extremely rare.
[+] [-] DanielBMarkham|6 years ago|reply
People forget that this discussion is not necessarily related to life. When various European explorers went out, in many cases they didn't know what to expect. When they met strange peoples, most of them refused to believe these were actually human.
It takes a good long while for humans to recognize other lifeforms like us. We naturally think that we're unique, that wherever we call home is special and the center of things. Combine that with galactic distances and it might be a good while before we realize that the universe is actually full of aliens that look just like humans only with bumpy heads (Obligatory Star Trek joke)
[+] [-] hirundo|6 years ago|reply
But if panspermia is true such critters in the cosmic wind would be cousins of life on earth, and it would be difficult (impossible?) to distinguish an alien microbe from domestic contamination. If it's false we see nothing, and wonder if it's because space is sterile or we're just not yet offering it the right primeval soup.
[+] [-] wycy|6 years ago|reply
[+] [-] DebtDeflation|6 years ago|reply
[+] [-] mywittyname|6 years ago|reply
The idea just doesn't jibe with my understanding of evolution.
[+] [-] koboll|6 years ago|reply
[+] [-] gremlinsinc|6 years ago|reply
[+] [-] titzer|6 years ago|reply
[+] [-] reggieband|6 years ago|reply
I commented today on a bit of dermatological discussion where they claim our skin has a biome of bacteria. This is in addition to the gut biome that is starting to look like it contributes to a wide array of human health issues. Part of me wonders how much of those biomes (e.g. how many bacteria within that biome) are from sources outside our planet.
[+] [-] rossdavidh|6 years ago|reply
[+] [-] ShamelessC|6 years ago|reply
[+] [-] AgentME|6 years ago|reply
[+] [-] newsgremlin|6 years ago|reply
[+] [-] Grustaf|6 years ago|reply
Yeah, but that sort of places us at the center of the universe, and all the force of history is to say, “Don’t think of us as the center. We’re nothing.””
What kind of argument is that? Sounds like some kind of anti-geocentric dogma, not an actual argument.
[+] [-] unknown|6 years ago|reply
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