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If life were discovered on Mars (other than that introduced by our instruments), it would demonstrate one of two possibilities depending on whether Martian life shared a common origin with Earth life:
INTERPLANETARY TRANSFER OF LIFE had happened, which would suggest that interstellar transfer of life was also possible.
Or
ABIOGENESIS occurred more than once in our solar system, which would suggest that abiogenesis was a probable outcome of a favorable environment in the rest of the universe.
Finding life anywhere else in our solar system would lead to similar conclusions.
The question as to whether life exists on Mars can be answered in the affirmative by one example of such life. Until such an example emerges, it is an open question. The negative cannot be proven by observation, and a theory that would preclude life on Mars does not seem to be anywhere in sight. Nonetheless, with no example of life on Mars and no proof of the negative, we can still make an EDUCATED ASSESSMENT.
We make such assessments all the time in the face of uncertainty and incomplete information. Will that store have soy free, vegetable butter? Is that Clint Eastwood movie worth seeing? Will Iran get the Bomb?
Back to Mars: At this point the observation is fairly robust that any life on Mars must not have been very successful; at least its effects on the Martian environment are minute compared to life on Earth. To review the observations:
Until the middle of the 20th century observations of the surface of Mars did not provide much evidence of anything, but for the last half century, increasingly sophisticated observations of the surface have been made from Earth, space and Mars itself. So far about two dozen spacecraft have successfully flown by or orbited Mars, and almost a dozen have landed on Mars. They have at least partially fulfilled the role of geologist over hundreds of kilometers of Martian surface. For over a century increasingly sophisticated observations of atmospheric gases have been made, now including those of Curiosity. Observations of the sub-surface have been made from an analysis of geologic structures currently on the surface, minor digging operations, Martian meteorites, and various remote imaging techniques applied to the sub-subsurface.
To summarize these observations:
ATMOSPHERIC GASES display no evidence of life. From Curiosity, “The initial SAM measurements place an upper limit of just a few parts methane per billion parts of Martian atmosphere, by volume, with enough uncertainty that the amount could be zero.” On the Earth it’s 2 parts per million even with our higher temperatures and 21% oxygen. No other gaseous product of life is evident.
SURFACE. For decades there have been orbiters photographing the entire Martian surface with resolutions down to sub-meters. On the Earth, of course, life is observed everywhere except in glacial areas, parts of the most extreme deserts, and most water covered areas (even there algae blooms and marine phosphorescence display in large parts of the water cover). A random sample of Earth’s surface has about one chance in three of observing life at a one meter square scale; on Mars the result is zero out of hundreds of trillions of observations.
SUB-SURFACE. Sedimentary layers observed from orbit and from the surface show no signs of fossils, no actions of life, no layers of calcium carbonate formed by planktonic algae, no other hint of the action of life. Martian meteorites display no evidence of life that convinces the scientific community. Our landers don’t find anything with their digging. Evidence of life is ubiquitous from such observations on Earth.
For over a century we've looked for life in increasingly capable ways that would have revealed its presence if that life had affected its environment within four or more orders of magnitude of the effects of Earth life. There has been no meaningful evidence of such life. Given these observations and the generally inhospitable environment of Mars, I would make the somewhat educated assessment that NO EXAMPLE OF INDIGENOUS LIFE WILL BE FOUND ON MARS.
Given that assessment, the lack of indigenous life on Mars is a bit surprising considering:
> the huge reservoir of very diverse life that has existed on Earth for the last four billion years
> that a lot of Earth material has landed on Mars in that time
> and that Mars had a more friendly environment for life in the past, which should have given life imported from Earth a chance to establish itself, evolve and adapt.
That life has not migrated to Mars, with four billion years of very substantial opportunity, implies that interplanetary transport of life is not all that easy, and that INTERSTELLAR TRANSPORT OF LIFE IS UNLIKELY.
Given that assessment, the lack of abiogenesis in such a favorable environment implies that ABIOGENESIS IS NOT ALL THAT COMMON.
The implications that interstellar transport of life is unlikely, and that abiogenesis is uncommon, are reinforced by the observation that we have also seen no evidence of ET beyond our solar system. These implications may also serve as an explanation for this Great Silence.
Last edited by bobunf (2012-11-30 10:27:57)
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The only question that I could raise would be whether we have actually explored the red planet enough to really say with any certainty that there is not now nor has there ever been life there. You contend that we do know enough to say with a reasonable degree of certainty that life does not exist on Mars. However, particularly with regards to past life, I don't believe that evidence is yet present. In my opinion, it is entirely feasible that life could have been transferred from Earth to Mars, or established on Mars itself, and then as the climate fell into disequilibrium and geological heat sources cooled was simply unable to replicate itself faster than the environment destroyed it. It is possible that the introduction of life is what caused this disequilibrium to occur in the first place. While life maintains internal homeostasis, there is nothing impossible or even uncommon about an organism entering an environment and through its growth making it unlivable. I do not claim that there is evidence for this but I do believe that it is plausible and cannot be ruled out based on the available evidence.
More importantly, however, you raise a largely unconsidered solution to the Fermi Paradox: Why does it look like the universe is devoid of intelligent life? Because it is.
-Josh
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The only question that I could raise would be whether we have actually explored the red planet enough to really say with any certainty that there is not now nor has there ever been life there. You contend that we do know enough to say with a reasonable degree of certainty that life does not exist on Mars. However, particularly with regards to past life, I don't believe that evidence is yet present. In my opinion, it is entirely feasible that life could have been transferred from Earth to Mars, or established on Mars itself, and then as the climate fell into disequilibrium and geological heat sources cooled was simply unable to replicate itself faster than the environment destroyed it. It is possible that the introduction of life is what caused this disequilibrium to occur in the first place. While life maintains internal homeostasis, there is nothing impossible or even uncommon about an organism entering an environment and through its growth making it unlivable. I do not claim that there is evidence for this but I do believe that it is plausible and cannot be ruled out based on the available evidence.
More importantly, however, you raise a largely unconsidered solution to the Fermi Paradox: Why does it look like the universe is devoid of intelligent life? Because it is.
I would agree. We know on Earth there are lots of microenvironments - sub oceanic hot springs, deep caves etc - where there are isolated ecologies that carry on happily for billions of years.
Until we have explored those potential environments on Mars, it is difficult to say what the state of play is. Also, Mars' atmosphere is at such low pressure that the comparison with Earth is somewhat questionable. Maybe life has been reduced to a few ice worms and ice bateria??
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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You contend that we do know enough to say with a reasonable degree of certainty that life does not exist on Mars.
I do not make that assertion. I suggest an educated assessment based only on what is now known. We make such assessments all the time. In life we rarely have the luxury of “a reasonable degree of certainty.” We very frequently have to make decisions based on incomplete, imperfect data. Would we make money advertising on the radio? Should we market porous point pens? Should we arm anybody in Syria? Who?
So, at this point in time, what do you think? Not based on wishes or fantasies, but on the observations, theory, logic and experience we currently possess. Life on Mars now? In the past?
I have problems with life existing on Mars now.
It’s hard to imagine finding much life on the surface of Mars, even bacteria. On Earth bacteria and algae leave unmistakable signs: changing the color of rocks, changes that last thousands of years even in Earth’s active climate. The entire surface of Mars has been examined rather closely from orbit, and millions of square meters at multiple locations by eight landers. Couple that with the hostile radiation, desiccation and chemical environment on the surface, and my educated assessment is that we are just not going to find life on the surface of Mars.
(Nearly?) all life on Earth produces identifiable gases. The Curiosity observation constrains the upper limit of methane at about 1,000th that on Earth. Earth has more robust means of eliminating methane; not all Earth life produces methane. There’s also a considerable probability that methane may be produced through non-biological processes on Mars. Even with this added boost, still methane on Mars is less than 1,000th that on Earth.
In more than a century no other gas (such as oxygen, ozone, or nitric oxides) has been observed out of thermal equilibrium by orders of magnitude. Mars life would have to produce gases at a rate many orders of magnitude less than life on Earth for this to be the case.
That leaves life limited to the sub-surface, producing no gases detectable in the atmosphere, using energy sources other than the Sun, and leaving no evidence in any of the samples and geologic structures we’ve studied to date. There could be redoubts in which small colonies of life have existed for the billions of years that Mars has been in its current inhospitable condition. But SMALL POCKETS OF LIFE ISOLATED FOR VERY LONG PERIODS OF TIME TEND TO DISAPPEAR; they use up their resources; things change; the nest gets fouled; the ecological niche collapses; they can’t move.
So my educated assessment is that WE WILL NOT FIND LIFE CURRENTLY EXTANT ON MARS BECAUSE IT’S NOT THERE. This could be because it was never there, or because it died out.
There have been a few observations that could detect extinct microbial life: effects on the Martian surface or in geologic formations, meteorites, and what landers may have examined. No signs of extinct life that the scientific community accepts.
If life ever did exist on Mars, how long will it be before a comprehensive search is mounted for microbial life that died out a few billion years ago? Not for a long time, I venture. Which means that, for the foreseeable future what we know now is what we will know for the next few decades.
Of course, after 10,000 scientists of various stripes have diligently searched for extinct life in ten million places on Mars, we still will not be able to say, “This proves no life ever existed on Mars.” While this proposition can never be proved, we might consider John Maynard Keyes admonition, “That all things are possible is no excuse for talking foolishly.”
Available today:
Some evidence that no life currently exists on Mars, because it’s effects, if any, are not detectable, and small quantities of life would probably have died out billions of years ago.
No extinct life in the places we’ve been able to look.
The simpler idea is that there is currently no life on Mars because there never was any. This implies that interplanetary (and even more so interstellar) transport of life is unlikely and that abiogenesis is rare.
Both implications supported by, and explaining, the Great Silence.
No certainly implied; just an educated assessment based only on our current state of knowledge.
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We know on Earth there are lots of microenvironments - sub oceanic hot springs, deep caves etc - where there are isolated ecologies that carry on happily for billions of years.
I'm not aware of any such that have lasted for billions of years. Could you enlighten me?
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The Great Silence implies that contemporary technological civilizations more advanced than ours must be rare. I think we have enough data about exo-planets to be able to say that a lack of habitable planets and moons is probably not the reason for the Great Silence. Even assuming that super-luminal travel, communication and observation are not practical, I still emphatically reject the idea that ETs would be uniformly uncommunicative.
They will certainly know we are here from the atmospheric gases that life has produced in very great quantities for the last four billion years. For those within a few thousand light years of Earth, the effects of large scale agriculture and metal working will have signaled the presence of a technological species on Earth for the last ten thousand years.
At least some ETs will not be monolithic, which means many groups within each ET civilization will provide evidence observable by us from engineering, altruistic, religious, ideological, academic or numerous other motives, many of which I haven’t thought of.
All of this suggests that the probability of a contemporary technological civilization must be considerably less than one per million star systems. One per million would leave about 400,000 contemporary technological civilizations in the Milky Way Galaxy. There would be about a thousand such civilizations within five thousand light years of Earth; a 90% probability of one such a civilization within 800 light years. It seems inconceivable that many of these would not be noticed.
That leaves three reasons for the Great Silence, for the rarity of contemporary technological civilizations:
1. Abiogenesis and interstellar transport of life are rare
2. Overcoming all of the numerous hurdles after abiogenesis and before a contemporary technological civilization emerges is rare. Hurdles such as the invention of photosynthesis, the development of multi-celled organisms, brain growth gone wild (as with Homo Sapiens), etc.
3. The lifetime of technological civilizations is short even considering that after the extinction of the biological entities, observable signs of the civilization may remain for eons in various artifacts such as legacy beacons, robots or interstellar probes in our solar system.
I hope that the third reason is not THE reason. What Mars has to say, to date, about abiogenesis and interstellar transport of life is comforting.
There is no constraint on the lower limit of the probability of a contemporary technological civilization per star system. There’s nothing to say it has to be more than one per billion, one per trillion, or one per google. This concept is a bit frightening since it leaves open the possibility that we are the ONLY one.
A new type of information about this issue will be produced before the end of the next decade; analysis of the atmospheric gases of habitable exo-planets will tell us if abundant life exists around other stars. If we find no such evidence, the data about Mars (and the rest of our solar system) will reinforce the idea that abiogenesis and interstellar transport of life is rare. The lifetime of technological civilizations will not necessarily be short. If we do find life, Mars will be an anomaly, and either the hurdles to technological civilization or the life span of such civilizations will be the answer to the Great Silence.
I’ll be 90 years old when this new data is flowing, and that will be my last glimpse of these questions – unless ET pops in for my hundredth.
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louis wrote:We know on Earth there are lots of microenvironments - sub oceanic hot springs, deep caves etc - where there are isolated ecologies that carry on happily for billions of years.
I'm not aware of any such that have lasted for billions of years. Could you enlighten me?
I was thinking sea vent communities must have lasted billions of years, evolving with the moving techtonic plates, but perhaps I got that wrong. Happy to amend billions to millions, perhaps hundreds of millions.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Yes,the Great Silence has always seemed pretty significant to me, especially as we are not in the early batch of stars, are we? So there ought already to be millions of civilisations well ahead of us in the cosmos. And only a few of those needs to develop pan-galactic technology for their presence to, surely, become blindlingly obvious.
How to explain it then? I am not sure we can at the moment.
Sir Martyn Rees is persuasive about the many risks to civilisation. It may well be there is a the equivalent of an elephant trap that nearly all civilisations fall into e.g. maybe there is some obvious, innocent and interesting looking scientific experiment that ends in the creation of a local black hole. That could explain it. It was raised as a danger with respect to the Hadron collider I believe. Maybe one or two civilisations have avoided it, but perhaps they are at the other end of the cosmos.
I can't really see any other explanation except that intelligent life is v.v. difficult to get started. After all we can see just 200 years after teh industrial revolution what robots are capable of. Another 100-200 years and who can doubt they could be capable of taking our civilisation (in robotic form) on long galactic voyages? So even if an organic civilisation dies, there ought to be a continuing robot presence.
I think people have remarked on how the moon has been crucial to the development of intelligent life on Earth, by creating much greater stability in orbit (at least I think that's what is meant). Well if true, getting a medium sized planet in the right goldilocks zone to capture/create through impact a body like the Moon might be quite rare in itself. If it's a 1 in a billion solar systems thing, then it coudl dramatically reduce the chances of life.
The Great Silence implies that contemporary technological civilizations more advanced than ours must be rare. I think we have enough data about exo-planets to be able to say that a lack of habitable planets and moons is probably not the reason for the Great Silence. Even assuming that super-luminal travel, communication and observation are not practical, I still emphatically reject the idea that ETs would be uniformly uncommunicative.
They will certainly know we are here from the atmospheric gases that life has produced in very great quantities for the last four billion years. For those within a few thousand light years of Earth, the effects of large scale agriculture and metal working will have signaled the presence of a technological species on Earth for the last ten thousand years.
At least some ETs will not be monolithic, which means many groups within each ET civilization will provide evidence observable by us from engineering, altruistic, religious, ideological, academic or numerous other motives, many of which I haven’t thought of.
All of this suggests that the probability of a contemporary technological civilization must be considerably less than one per million star systems. One per million would leave about 400,000 contemporary technological civilizations in the Milky Way Galaxy. There would be about a thousand such civilizations within five thousand light years of Earth; a 90% probability of one such a civilization within 800 light years. It seems inconceivable that many of these would not be noticed.
That leaves three reasons for the Great Silence, for the rarity of contemporary technological civilizations:
1. Abiogenesis and interstellar transport of life are rare
2. Overcoming all of the numerous hurdles after abiogenesis and before a contemporary technological civilization emerges is rare. Hurdles such as the invention of photosynthesis, the development of multi-celled organisms, brain growth gone wild (as with Homo Sapiens), etc.
3. The lifetime of technological civilizations is short even considering that after the extinction of the biological entities, observable signs of the civilization may remain for eons in various artifacts such as legacy beacons, robots or interstellar probes in our solar system.I hope that the third reason is not THE reason. What Mars has to say, to date, about abiogenesis and interstellar transport of life is comforting.
There is no constraint on the lower limit of the probability of a contemporary technological civilization per star system. There’s nothing to say it has to be more than one per billion, one per trillion, or one per google. This concept is a bit frightening since it leaves open the possibility that we are the ONLY one.
A new type of information about this issue will be produced before the end of the next decade; analysis of the atmospheric gases of habitable exo-planets will tell us if abundant life exists around other stars. If we find no such evidence, the data about Mars (and the rest of our solar system) will reinforce the idea that abiogenesis and interstellar transport of life is rare. The lifetime of technological civilizations will not necessarily be short. If we do find life, Mars will be an anomaly, and either the hurdles to technological civilization or the life span of such civilizations will be the answer to the Great Silence.
I’ll be 90 years old when this new data is flowing, and that will be my last glimpse of these questions – unless ET pops in for my hundredth.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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I've read about this stabilizing moon idea for awhile. I don't buy it. Our Moon disturbing the delicate things taking place (maybe) in the tidal pools that lead to life. It does other things like lengthen the day.
As for climatic instability, how relevant could that be in the oceans? And assuredly those climatic instabilities would be less extreme than the more or less periodic glaciations Earth has experienced in the last 3 million years. The other non-periodic glaciations, including snowball Earth of six hundred million years ago and maybe other times in the past. It's effects less extreme than the numerous impacts Earth has experienced producing mass extinction events.
Then there are the moons of gas giants as potential homes for life. They wouldn't need a moon.
I think more likely explanations are the rarity of abiogenesis (if it is rare), and the barriers imposed by the necessity to invent photosynthesis, multicellar structures and ridiculously sized brains. Last, and hopefully least likely, that the life span of technological civilizations is very brief even accounting for robots, beacons, probes and other artifacts.
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