Evidence for ET is mounting daily, but not proven.

[Evan]

Naturally I haven't read all 500+ replies. However, the beginning and the tail of this thread do not differ greatly.

Evidence for life elsewhere is not mounting. We don't even have evidence for how life began here. We have many assumptions, wild guesses and informed speculation but we have no idea what the initial conditions were here on Earth that led to the chance occurrence of a self organizing and self replicating organism. Without even that basic knowledge we don't know what to look for elsewhere. We can be reasonably certain that the early atmosphere on Earth wasn't anything like it is today. Free oxygen doesn't hang around for very long without life to replenish it.

The life forms that exist here today are those that have adapted to current conditions. There is also a very large element of pure luck that allowed some types to survive purely by chance when great extinction events occurred. A life form cannot evolve to survive an extinction event nor can it adapt in just a few generations or even a few thousand to survive conditions that are deadly. We do have evidence that a majority of the life forms that existed previously on Earth have failed to survive. The remains of the creatures that are found in the Burgess Shales represent forms of life that were utterly wiped out. They have no present day descendants, nothing that can in any way be reasonably connected to the forms that existed before the event that finished them.

We are lucky that we live in a quiet corner of the galaxy. Of course if we didn't we wouldn't be be here. What is becoming apparent is that galaxies are high energy neighbourhoods and that isn't good news for self organizing, complex anythings. Energetic events have a strong ability to tear things apart. Huge swaths of any galaxy are off limits to anything that depends on persistent structure and organization. High energy environments are inimical to what we consider to be life. Even life that we might not recognize is not exempt from the intensely disordering effects of high energy processes. Wide spectrum high level electromagnetic radiation will disrupt even basic organic molecules as well as inorganic molecules.

This is something for which we are rapidly developing evidence. A black holes forms at the centre of every galaxy and infalling matter spews intense radiation like a Flash Gordon death ray. There is no chance for life to develop, let alone survive, anywhere near the central regions of a galaxy. The Drake Equation needs a few more terms to accurately describe what we now know about our universe. Those terms are essentially negative constants that reduce the probability of life surviving long enough to be noticed. The terms need to include the chances of various extinction events occurring to any particular planet that might give rise to a life form. Everything from simple asteroid impacts to hyper novas in the neighbourhood represent terminal events. Put even weak wild guesses into the equation and what comes out can easily be a negative chance of life developing in any particular galaxy, never mind lasting long enough to develop to a sentient level.

On top of all that we have no idea what it takes for life to go from a self replicating organic soup to something that is able to contemplate that process.

[baric]

We don't even have evidence for how life began here.

I stopped reading right there.

[CaptainToonces]

On top of all that we have no idea what it takes for life to go from a self replicating organic soup to something that is able to contemplate that process.

Actually we have a pretty good idea of one example of that, it's called the history of the Earth. And in fact we don't know the history of any other planets in the universe nearly as well so it's difficult to speculate what they might be like, but why should this one be so rare...

You said that adding the chances of extinction events to the drake equation could give negative chances of life developing in a galaxy. That is false, as that equation cannot mathematically produce a "negative chance". Chances just get closer to 0.

No extinction event has ever wiped out life on Earth, just decimated it.

As far as I know studies have shown that if you take a planet like Earth, in the goldilocks zone where water is liquid, there's a high chance of self-replicating organic soup.

[Evan]

I stopped reading right there.

Why? Perhaps you assumed something you shouldn't? If you think we have evidence for how life began on this planet how about detailing the steps at the biochemical level. I'll wait. A good place to start is with explaining the self organization of a complex chemical structure. We have very little clue how that works and we cannot replicate it at this time. The next hurdle in explaining it is to demonstrate how a self organizing structure can then self replicate a nearly perfect copy of itself.

As to my statement "We don't even have evidence for how life began here.", how about refuting it if you can? Last time I checked there isn't a shred of evidence existing from the time of the origin of life on this world. We don't even have a good handle on when that was.

[Evan]

No extinction event has ever wiped out life on Earth, just decimated it.

Oh? How do you know that? How many times has life restarted on this planet?

As far as I know studies have shown that if you take a planet like Earth, in the goldilocks zone where water is liquid, there's a high chance of self-replicating organic soup.

Apparently not all that high or we would have already done it.

[IsaacKuo]

Oh? How do you know that? How many times has life restarted on this planet?

The fossil record goes back at least 2.7 billion years and perhaps 3.5 billion years. That leaves perhaps a billion years or so before that in which it's possible there was life on Earth which was completely wiped out.

In particular, it's plausible that the Late Heavy Bombardment may have wiped out all life on Earth (if any existed at the time). If so, then it must be very easy for abiogenesis to occur quickly since we have fossil evidence of life so shortly afterward. On the other hand, it's plausible that life may have survived through the Late Heavy Bombardment.

[baric]

Why? Perhaps you assumed something you shouldn't?

Because it ignores 150 years of biological study? It's a blatantly incorrect assertion.

[Evan]

Pure speculation does not constitute evidence. The point is that we have no evidence that explains how life began. There are plenty of guesses that are based on a stack of assumptions bolstered by some serious hand waving, but there is no evidence. We do not know how life began and we may never know. There is nothing left of that time to examine and even if there were it is unlikely that they earliest living organism would leave anything permanent behind when disincorporated for any reason. It is impossible to give any sort of reasonable account of the origin of life on Earth without invoking speculation and assumptions. Since we live here and have direct access to the existing natural history of this planet but cannot determine these factors we are clearly not in a position to establish the parameters of what actually constitutes an exo-world suitable for the origin of life. We can safely say what it takes to support life now but that isn't the same thing. Since we don't know the conditions on this planet at the time life began and succeeded in staying alive we don't know what we are looking for. In particular, what was the constitution of the early atmosphere of Earth? That is directly relevant to recognizing an "Earth like" planet since it is one of the few parameters that we may be able to acertain in the near future.

[Evan]

Because it ignores 150 years of biological study? It's a blatantly incorrect assertion.

Please reread my statement. "We don't even have evidence for how life began here."

What evidence do we have for the process that resulted in the origin of life? We have not accomplished it and we haven't observed it. I have yet to see a detailed description of how it works.

[baric]

Pure speculation does not constitute evidence. The point is that we have no evidence that explains how life began.

This is a classic moving of the goalposts that is similar to the "god of the gaps" arguments in theological discussions.

We have a tremendous amount of evidence about the origin of life on this planet. Just two centuries ago, there was no concept of common descent -- most people assumed divine creation.

Since then, we have learned:
1) Man shares a common ancestor with apes
2) Hominids share a common ancestor with all mammals
3) ALL LIVING CREATURES share a common ancestor

We have discovered the inner workings of the cell and the function of mitochondria and ATP for energy. We have discovered DNA and how it creates variation through generations.

We have sequenced the DNA of bacteria to understand the effects of genes and proteins (way over my head at this point). We have learned enough to refute the "irreducible complexity" arguments about bacterial flagella.

We have literally pushed our understanding about the creation of life on this planet all of the way back to the level of RNA, proteins and genes.

On the other end, from the ground up, we have learned about how easily complex hydrocarbons and other necessary components for life are created by purely natural and undirected chemical processes.

Frankly, to dismiss all of that intellectual progress (AND EVIDENCE) with a blanket assertion like "We don't even have evidence for how life began here" makes you look either very uninformed or cynical.

Just because we have not established a 100% chemical trail from cometary ice to functioning biological organisms does not mean we lack evidence.

Is that what you wanted to hear?

[baric]

Please reread my statement. "We don't even have evidence for how life began here."

I'm not playing your goalpost game.

[Evan]

What goalpost game? I haven't changed anything from my original assertion. We do not know how life began on Earth. We have no reason to believe that RNA and DNA that we know now is the same as what the earliest life forms used to encode information about their own structure. It is much more reasonable that such encoding was a product of evolution just as everything else seems to be. It is very important in scientific enquiry to separate what we know from what we believe, assume and speculate to be so.

We have literally pushed our understanding about the creation of life on this planet all of the way back to the level of RNA, proteins and genes.

We have no evidence that those methods were employed by the aboriginal life forms. They MAY be a product of evolution. There is no evidence either way but Occam's razor argues aginst such a high order of complexity for the earliest organisms. To give you some idea of the level of complexity present in current life forms, it has recently been determined just how many proteins take part in a synapse during the forming of a memory. Just one synapse, not an entire complex memory, requires the participation of over 1,400 proteins. That applies to life forms as lowly as Planaria, not just humans.

Please don't use the term "creation". That implies a creator.

[Evan]

I just did a quick check and found that the very oldest DNA ever found is only 419 million years old. That leaves a gap of as much as 3 billion or so years that still needs explaining.

[IsaacKuo]

I just did a quick check and found that the very oldest DNA ever found is only 419 million years old. That leaves a gap of as much as 3 billion or so years that still needs explaining.

Why do you think this?

Note that most of our information about DNA and its historical development comes from analysis of the DNA of living species.

[Canis Lupus]

As far as I know studies have shown that if you take a planet like Earth, in the goldilocks zone where water is liquid, there's a high chance of self-replicating organic soup.

Great. I would be grateful for some links to the studies, however, I am puzzled by the description, "self-replicating organic soup". Maybe the studies can assist.

[baric]

What goalpost game? I haven't changed anything from my original assertion. We do not know how life began on Earth.

That's not what you said, nor what I was objecting to. You said:

""We don't even have evidence for how life began here."

And yes, this is goalpost-shifting whether you realize it or not. There is absolutely no way we will ever know with 100% certainty how life began on Earth since most of that trail is lost in history.

In other words, no matter how much evidence we find about the origins of life on Earth (including what I listed), people will always be able to shift the goalposts back a little further and claim that we don't really know.

This is logically no less flawed than the "god of the gaps" argument or the neverending search for the missing evolutionary link.

[CaptainToonces]

Great. I would be grateful for some links to the studies, however, I am puzzled by the description, "self-replicating organic soup". Maybe the studies can assist.

Here ya go:
http://en.wikipedia.org/wiki/Origin_...soup.22_theory

Miller-Urey: http://en.wikipedia.org/wiki/Miller%...rey_experiment

Why is it so hard to believe that if you take a water world with carbon, nitrogen, etc. and add millions of years and sunlight that "life" wouldn't explode all over it?

[Evan]

This is logically no less flawed than the "god of the gaps" argument or the neverending search for the missing evolutionary link.

Hardly. My original statement stands. It is very relevant to finding other worlds that might harbor life since whe need to know what to look for. Looking is our only option and the only tool available in the forseeable future will be to identify something in the spectra of exoplanets that unambiguously points to a living process. Free oxygen is a very good indicator since it has a very short lifetime if it isn't replenished by life forms here on Earth. However, if we are limited to looking only for planets that have free oxygen we may be limiting our search to a very small percentage of the planets that bear life.

What about the early protolife on Earth? It didn't use a metabolic cycle that depended on free oxygen, we can be sure of that much. The Earth would have been very chemically active in the early phases of the development of life and the metabolic cycles that the vast majority of life now on Earth depend on would not have been possible. Some other energy cycle must have been available and some other metabolic side product might be detectable in the atmosphere of such a planet. Knowing what to look for might expand the possiblities by orders of magnitude if life is routinely wiped out by the very nature of the galaxies we live in. Right now we do not know what to look for since we do not know the early history of life on this planet.

It isn't a question of moving goalposts. The identification of proto life depends on us knowing how it works.

[CaptainToonces]

Oh? How do you know that? How many times has life restarted on this planet?

I doubt it has ever had to restart once it got started. When you do your dishes do you think that you eradicate every last bacterium on them?

I will grant you that there may be some events that can happen over 4 billion years to completely sterilize a life planet but these are not on the order of asteroid impacts we have endured here. Such events would have to be planet-planet collisions or some such amazingly destructive event it would take to really kill off 100% of the bacteria here.

[Canis Lupus]

Perhaps it's a differing level of evidence which an individual will be satisfied with which is causing the disagreement. Some are content with a sketchy picture as being ample enough evidence, while others want something more exact.

As has been stated, it may well be impossible to determine how life started on Earth, but if experiments attempting to produce life through abiogenesis are successful, we'd have a fairly strong indicator. Until then, or until some other observation indicates another source, I would have to agree with Evan that "we don't have evidence for how life began here", although we do have ample evidence that life has begun here. Obviously, it would be a good idea for further and on-going enquiry not to confuse the two.

In relation to moving goal posts, which can be quite frustrating during discussion, even allowing for the inevitable refinement of positions which occur during fruitful discussions, lumbering someone with a 100% certainty requirement seems quite a shift. Did Evan ever require such a thing?

[Evan]

Why is it so hard to believe that if you take a water world with carbon, nitrogen, etc. and add millions of years and sunlight that "life" wouldn't explode all over it?

It isn't particularly hard to believe until you look at the details. That early world may not have much sunlight at the surface. It probably had continuous acid rain from high levels of sulphur in the atmosphere. Ionizing radiation background levels would be many times higher than the are now. Instead of conditions being especially favorable they may have been especially unfavorable with the result that life has only a slim chance of getting going on a permanent basis. Living forms are demonstrably easy to kill. Current life forms cannot tolerate very much variation in conditions. There are only a very few exceptions to that general principle and they are all very low level forms of life such as Radiodurans. The fact that Radiodurans is still here suggests that it was an evolutionary dead end but it also suggests that conditions were much more hostile than we suspect.

I counter with another question. Why is it so hard to believe that high energy events which demonstrably exist in abundance would wipe out most of the life that does manage to get started?

I must go to town so I will check back this evening.

[Canis Lupus]

Here ya go:
http://en.wikipedia.org/wiki/Origin_...soup.22_theory

Miller-Urey: http://en.wikipedia.org/wiki/Miller%...rey_experiment

Why is it so hard to believe that if you take a water world with carbon, nitrogen, etc. and add millions of years and sunlight that "life" wouldn't explode all over it?

I may have missed some detail but I found no reference to anything "self-replicating" in the linked to wiki entry about the study.

[CaptainToonces]

I counter with another question. Why is it so hard to believe that high energy events which demonstrably exist in abundance would wipe out most of the life that does manage to get started?

Well, because that's not what we observe in the fossil record, and it doesn't make common sense either. The fossil record shows that even the worst extinction events here have reduced the biodiversity of species, but have not come close to threatening the existence of life on Earth (http://en.wikipedia.org/wiki/Extinction_event).

Common sense tells you what i said with my dish washing analogy. You can subject that dish to all sorts of bleach, boiling water, radiation, whatever, and one lucky bacterium out of the millions on there is going to find a protected crevice and survive.

[baric]

Hardly. My original statement stands. It is very relevant to finding other worlds that might harbor life since whe need to know what to look for. Looking is our only option and the only tool available in the forseeable future will be to identify something in the spectra of exoplanets that unambiguously points to a living process. Free oxygen is a very good indicator since it has a very short lifetime if it isn't replenished by life forms here on Earth. However, if we are limited to looking only for planets that have free oxygen we may be limiting our search to a very small percentage of the planets that bear life.

What about the early protolife on Earth? It didn't use a metabolic cycle that depended on free oxygen, we can be sure of that much. The Earth would have been very chemically active in the early phases of the development of life and the metabolic cycles that the vast majority of life now on Earth depend on would not have been possible. Some other energy cycle must have been available and some other metabolic side product might be detectable in the atmosphere of such a planet. Knowing what to look for might expand the possiblities by orders of magnitude if life is routinely wiped out by the very nature of the galaxies we live in. Right now we do not know what to look for since we do not know the early history of life on this planet.

It isn't a question of moving goalposts. The identification of proto life depends on us knowing how it works.

What cracks me up about your insistence that we don't have evidence of how life arose is that you rely on such evidence to make your case.

How exactly can you make authoritative statements about the metabolic cycle of protolife on Earth? Why are you so sure about what is likely or not likely? Are you just pulling those arguments out of thin air or are they based on evidence gathered about the inner workings of the simplest forms of life on this planet?

[KABOOM]

Naturally I haven't read all 500+ replies. However, the beginning and the tail of this thread do not differ greatly.

Evidence for life elsewhere is not mounting. We don't even have evidence for how life began here. We have many assumptions, wild guesses and informed speculation but we have no idea what the initial conditions were here on Earth that led to the chance occurrence of a self organizing and self replicating organism. Without even that basic knowledge we don't know what to look for elsewhere. We can be reasonably certain that the early atmosphere on Earth wasn't anything like it is today. Free oxygen doesn't hang around for very long without life to replenish it.

The life forms that exist here today are those that have adapted to current conditions. There is also a very large element of pure luck that allowed some types to survive purely by chance when great extinction events occurred. A life form cannot evolve to survive an extinction event nor can it adapt in just a few generations or even a few thousand to survive conditions that are deadly. We do have evidence that a majority of the life forms that existed previously on Earth have failed to survive. The remains of the creatures that are found in the Burgess Shales represent forms of life that were utterly wiped out. They have no present day descendants, nothing that can in any way be reasonably connected to the forms that existed before the event that finished them.

We are lucky that we live in a quiet corner of the galaxy. Of course if we didn't we wouldn't be be here. What is becoming apparent is that galaxies are high energy neighbourhoods and that isn't good news for self organizing, complex anythings. Energetic events have a strong ability to tear things apart. Huge swaths of any galaxy are off limits to anything that depends on persistent structure and organization. High energy environments are inimical to what we consider to be life. Even life that we might not recognize is not exempt from the intensely disordering effects of high energy processes. Wide spectrum high level electromagnetic radiation will disrupt even basic organic molecules as well as inorganic molecules.

This is something for which we are rapidly developing evidence. A black holes forms at the centre of every galaxy and infalling matter spews intense radiation like a Flash Gordon death ray. There is no chance for life to develop, let alone survive, anywhere near the central regions of a galaxy. The Drake Equation needs a few more terms to accurately describe what we now know about our universe. Those terms are essentially negative constants that reduce the probability of life surviving long enough to be noticed. The terms need to include the chances of various extinction events occurring to any particular planet that might give rise to a life form. Everything from simple asteroid impacts to hyper novas in the neighbourhood represent terminal events. Put even weak wild guesses into the equation and what comes out can easily be a negative chance of life developing in any particular galaxy, never mind lasting long enough to develop to a sentient level.

On top of all that we have no idea what it takes for life to go from a self replicating organic soup to something that is able to contemplate that process.

I find your thought process to be very inconsistent. While you (properly) caution on numerous fronts that we have "no evidence" with respect to life other than on Earth, you state other equally speculative opinions as if they were facts.

"the chance occurrence" of a replicating system starting on Earth, implies it was a long shot or blind luck. You, nor anyone else, know this. The right conditions in the GZ for enough time may result in life virtually all of the time or only 1 in a billion. There is no hard evidence towards either end of the spectrum.

Similarly, your statement of fact that it was pure "random luck" as to which species survived extinction events. Enough to refill every diverse inhabitable niche on the planet at least twice.

Similarly, your statments of "fact" that life can only survive on the outer fringes of a galaxy.

[Canis Lupus]

Well, because that's not what we observe in the fossil record, and it doesn't make common sense either. The fossil record shows that even the worst extinction events here have reduced the biodiversity of species, but have not come close to threatening the existence of life on Earth (http://en.wikipedia.org/wiki/Extinction_event).

Common sense tells you what i said with my dish washing analogy. You can subject that dish to all sorts of bleach, boiling water, radiation, whatever, and one lucky bacterium out of the millions on there is going to find a protected crevice and survive.

Didn't Evan use the phrase "most of life", yet your post appears to be addressing the idea of "all of life". You seem to be arguing with your own idea, not someone else's.

I counter with another question. Why is it so hard to believe that high energy events which demonstrably exist in abundance would wipe out most of the life that does manage to get started?

[CaptainToonces]

Canis, I took his "most" in that statement to refer to "most of the planets in the galaxy where life gets started are fully sterilized by extinction events." Perhaps I misinterpreted his meaning, or perhaps you did. Either way, he is arguing that the events we refer to as extinction events are responsible for the Fermi paradox which is not true, because life on the Earth, for example, recovered rather quickly from these events and was never really threatened by them.

Now, there could be longer-term sterilization events, such as what presumably happened with Mars losing its atmosphere for lack of a magnetic field.

[eburacum45]

I broadly agree with Evan in that it may never be possible to pin down exactly how life started on Earth. Perhaps the only way to do that with any certainty is to find a broad cross-section of young Earth-like planets in various stages of development, and find out what stage (if any) abiogenesis has reached on each of them. This might give a good indication of how life started on our own planet.

Or, quite possibly it may not. It may be the case that there are several routes to abiogenesis, and the Early Earth might have supported more than one of them; if (by any chance) the end results are reasonably similar, we may never know exactly which route to abiogenesis was followed by the Early Earth. After examining many Earth-like worlds in detail and replicating the various processes in the lab, there still may be some doubt in this field.

[Canis Lupus]

Canis, I took his "most" in that statement to refer to "most of the planets in the galaxy where life gets started are fully sterilized by extinction events." Perhaps I misinterpreted his meaning, or perhaps you did. Either way, he is arguing that the events we refer to as extinction events are responsible for the Fermi paradox which is not true, because life on the Earth, for example, recovered rather quickly from these events and was never really threatened by them.

Now, there could be longer-term sterilization events, such as what presumably happened with Mars losing its atmosphere for lack of a magnetic field.

Yep, your interpretation is more consistent with his original post.

[Luckmeister]

Here's an interesting interview with Jeffrey L. Bada regarding recent discoveries pertaining to the 1950 Stanley Miller experiments.