Mars Soil Resembles Veggie-Garden Dirt, Lander Finds

[Selfsim]

Bacteria and other microbes can certainly have a healthy eco-system without "the known healthy influence of higher trophic levels". Right here on Earth, for about 3 billion years the eco-system consisted of microbes only. The Cambrian explosion, which gave rise to those "higher trophic levels" was a mere half billion years ago — a very recent experiment, whose long-term viability remains uncertain.

So Mars is about the same age as Earth. If life in the form of bacteria developed on Mars in the past, then why would it just stop at bacterial levels?

Whilst the causes of the Earth's so-called 'Cambrian Explosion' have never been shown to be clear-cut, theories covering the emergence of species complexity turn out to be an inseparable mixture of ecological, environmental, developmental (evolutionary genetics) and complexity thresholding. I would have thought Mars would not be excluded from any of these so-called 'universal' phenomena? If not, then why would we prefer searches for bacteria? After all, I thought 'once life gets started', its evolution is inevitable as far as Astrobiology is concerned?

This' bacteria boundary' seems to be more like a mental block than any logical consequence of any current evidenced-based theories.

Why is Mars being treated as a pariah planet by our faithful and intrepid exo-life hunters?

[neilzero]

Because of what we know already about present Mars surface conditions, we think previous life on Mars (if any) could presently only survive several meters or more below the surface without advanced technology. We have not searched significantly below the surface of off world bodies, but we have found some fosils, but we were unable determine if they were ever living.
I suppose there is a minute possibity of high tech Martians presently living beneath the surface who have choosen to avoid contact with our rovers, or even high tech Martians living on the surface in locations we have not explored yet = about 99% of the surface area of Mars.
My guess is simple life forms do not evolve into higher life forms, that survive, unless there is a viable environmental niche for higher life forms.
Possibly some of what Selfism typed is minority opinion instead of mainstream, but I have zero formal education on the topic since grade school 67 years ago. Neil

[Ara Pacis]

So Mars is about the same age as Earth. If life in the form of bacteria developed on Mars in the past, then why would it just stop at bacterial levels?

Whilst the causes of the Earth's so-called 'Cambrian Explosion' have never been shown to be clear-cut, theories covering the emergence of species complexity turn out to be an inseparable mixture of ecological, environmental, developmental (evolutionary genetics) and complexity thresholding. I would have thought Mars would not be excluded from any of these so-called 'universal' phenomena? If not, then why would we prefer searches for bacteria? After all, I thought 'once life gets started', its evolution is inevitable as far as Astrobiology is concerned?

This' bacteria boundary' seems to be more like a mental block than any logical consequence of any current evidenced-based theories.

Why is Mars being treated as a pariah planet by our faithful and intrepid exo-life hunters?

On the contrary, the theories seem to be based on the only evidence for the conditions useful for life that we have. If those theories suggest that the particulars of the planet of Mars made it stop being conducive to life in general or in relation to a certain level of complexity at a certain location on the planet, then what's the problem?

[ASTRO BOY]

So Mars is about the same age as Earth. If life in the form of bacteria developed on Mars in the past, then why would it just stop at bacterial levels?

Whilst the causes of the Earth's so-called 'Cambrian Explosion' have never been shown to be clear-cut, theories covering the emergence of species complexity turn out to be an inseparable mixture of ecological, environmental, developmental (evolutionary genetics) and complexity thresholding. I would have thought Mars would not be excluded from any of these so-called 'universal' phenomena? If not, then why would we prefer searches for bacteria? After all, I thought 'once life gets started', its evolution is inevitable as far as Astrobiology is concerned?

This' bacteria boundary' seems to be more like a mental block than any logical consequence of any current evidenced-based theories.

Why is Mars being treated as a pariah planet by our faithful and intrepid exo-life hunters?

Probably simply because Mars never maintained Earth like conditions long enough for anything more complex then bacterial life to arise....
I envisage the inevitability of further evolution to depend on those conditions.

[ASTRO BOY]

This' bacteria boundary' seems to be more like a mental block than any logical consequence of any current evidenced-based theories.

Why is Mars being treated as a pariah planet by our faithful and intrepid exo-life hunters?

It's not nor ever has been.
Astrobiologists and cosmologists procede on current observational evidence based on evidence of conditions on individual planets..

[Selfsim]

On the contrary, the theories seem to be based on the only evidence for the conditions useful for life that we have. If those theories suggest that the particulars of the planet of Mars made it stop being conducive to life in general or in relation to a certain level of complexity at a certain location on the planet, then what's the problem?

Now let me get this straight .. the theories we rely on which anticipate the presence of sub-surface bacterial life on Mars (and lead towards microscopes being sent), also somewhat inconveniently, predict the ultimate evolution of predators*. However, because there's no present macroscopic evidence of the ubiquitous and homogenous spreading of primary producers and larger primary, secondary and tertiary consumers, (like there is on Earth), the assumptions made about Mars' past conditions by those same theories, must somehow differ from Earth's case(??)

But come what may, those same assumption categories, which also lead to the inevitability of the emergence of life on a past water abundant, goldilocks zone planet like Mars, must however, be fixed in stone, and are not permitted the same luxury of variation and sensitivities to environmental change, when it comes to the emergence phase, eh?

Well that sounds logical and consistent … (err .. not .!.)


Footnote:
* Predation imposes competitive evolutionary pressures leading to improved survivial opportunities for prey possessing physical advantages. Successive offspring of that prey and predators, ultimately develops more complex macroscopically visible characteristics over time (according to theory). Predation has been around a lot longer than the Cambrian Era, also ..

Predation appears to have become a major selection pressure shortly before the Cambrian period—around 550 million years ago—as evidenced by the almost simultaneous development of calcification in animals and algae and predation-avoiding burrowing. However, predators had been grazing on micro-organisms since at least 1,000 million years ago.

… That was pushed to ~2 bya in a recent study finding on macroscopic evidence of heterotrophic microbes and fossils of their prey in Canada. (The chemical metabolism evidence goes even further back to ~3.5 bya as well). Whilst these are admittedly small critters, let's not forget the evolution of abundant larger scale species, which ultimately evolved and inhabited the Earth subsequently. Adaptation of the extant species didn't stop in spite of the build-up of toxic, 'sterilising gases' (as far as the predominant species of that era is concerned .. Ie: O₂'s effect on cyanobacteria). So why assume similar causes (eg: UV irradiation, etc) prevented evolution towards larger 'more complex' species in Mars' instance?

(As an aside, the large 'bulls-eye' structure left behind by these 'Gunflintia' creatures should also 'likely' be present on Mars (as their signatures of existence). 'We don't need no microscopes' to see that on Mars! .. So where are these supposed to be hiding? )

Why is the evidence of the absence of larger 'more complex' species so readily overlooked, in preference for the adoption of the belief that scant, underground microscopic bacteria 'must' still exist on Mars?

Where's the consistency?

[Ara Pacis]

Now let me get this straight .. the theories we rely on which anticipate the presence of sub-surface bacterial life on Mars (and lead towards microscopes being sent), also somewhat inconveniently, predict the ultimate evolution of predators*. However, because there's no present macroscopic evidence of the ubiquitous and homogenous spreading of primary producers and larger primary, secondary and tertiary consumers, (like there is on Earth), the assumptions made about Mars' past conditions by those same theories, must somehow differ from Earth's case(??)

I know it might sound like circular reasoning but for one fact: Mars is demonstrably different from Earth. Theories that predict one set of occurrences on Earth might either not apply, or might apply but have different results.

But come what may, those same assumption categories, which also lead to the inevitability of the emergence of life on a past water abundant, goldilocks zone planet like Mars, must however, be fixed in stone, and are not permitted the same luxury of variation and sensitivities to environmental change, when it comes to the emergence phase, eh?

Well that sounds logical and consistent … (err .. not .!.)

There's a distinction to be made between applying the same theory to a different variable and getting variable results, and varying the theory to get the same results. If we had evidence that the results were the same, we might work backwards to find an explanation for why the theory was wrong. However, contradictory evidence suggesting that the theory is wrong with regard to Mars does not currently exist (as far as I am aware).

[Colin Robinson]

After all, I thought 'once life gets started', its evolution is inevitable as far as Astrobiology is concerned?

Do astrobiologists say evolution is sure to produce similar results in different environments? Which astrobiologists say that?

Why is the evidence of the absence of larger 'more complex' species so readily overlooked,

Perhaps because once it was understood what the Martian atmosphere is like (how thin, and how low in free oxygen), scientists didn't expect large complex organisms. So "evidence" of their "absence" came as no surprise.

in preference for the adoption of the belief that scant, underground microscopic bacteria 'must' still exist on Mars?

Do astrobiologists say Martian microbes "must" exist? Or do they say Martian microbes may exist, and it would be scientifically valuable to develop ways to find out?

[ASTRO BOY]

Do astrobiologists say evolution is sure to produce similar results in different environments? Which astrobiologists say that?



Perhaps because once it was understood what the Martian atmosphere is like (how thin, and how low in free oxygen), scientists didn't expect large complex organisms. So "evidence" of their "absence" came as no surprise.



Do astrobiologists say Martian microbes "must" exist? Or do they say Martian microbes may exist, and it would be scientifically valuable to develop ways to find out?

Logical approach, logical questions with logical answers....

[Selfsim]

After all, I thought 'once life gets started', its evolution is inevitable as far as Astrobiology is concerned?

Do astrobiologists say evolution is sure to produce similar results in different environments? Which astrobiologists say that?

No .. and I personally wouldn't apply a generalisation as all encompassing as that. (Its not what said above).
Certain basic, high level features of 'Evolution' are intrinsic to NASA Astrobiology's definition of 'life', for example.

(I can't be sure of course, but I might also be tempted to bet that folk here such as 'Paul Wally', (for eg), and 'TooMany', would also likely embrace the concept of universality of Evolution wherever life emerges .. based on past conversations, that is).

From the NASA Astrobiology Roadmap:

As a consequence of geological, climatologic, and microbial processes acting across geological time scales, the physical-chemical environments on Earth have been changing, thereby determining the path of evolution of subsequent life. For example, the release of molecular oxygen by cyanobacteria as a by-product of photosynthesis as well as the colonization of Earth’s surface by metazoan life contributed to fundamental, global environmental changes. The altered environments, in turn, posed novel evolutionary opportunities to the organisms present, which ultimately led to the formation of our planet’s major animal and plant species. Therefore, this “co-evolution” between organisms and their environment is an intrinsic feature of living systems.

Thus, Evolution is inevitable .. it is 'intrinsic' to how living systems develop over geological timespans.

Perhaps because once it was understood what the Martian atmosphere is like (how thin, and how low in free oxygen), scientists didn't expect large complex organisms. So "evidence" of their "absence" came as no surprise.

According to the Mars Ocean hypothesis, early Mars would have had a thicker atmosphere to allow liquid water on the surface and would have been fairly similar to Earth's. Given that large complex organisms developed comparatively rapidly here on Earth, there seems to have been opportunities for the same to have have happened on Mars, given an extant microbe population, (and given present theory on Mars' geological history .. which is now based on on-site geological evidence gathered by the rovers).

Do astrobiologists say Martian microbes "must" exist?

My comment was in keeping with the fundamental quest for detection of Martian microbial life, which is the general subject of this thread.

Some here, (and perhaps Levin), seem to be unswervably convinced that microbial life on Mars exists .. and in his case, has perhaps already been detected. The synergy between Earthly test results and Martian Viking results, appears to now being used as 'evidence' in support of the conviction that it exists there.

Or do they say Martian microbes may exist, and it would be scientifically valuable to develop ways to find out?

Surely we already know of the ways to find out! We have heaps of microbes here to test the detection of them! (Hence the 'vegie-garden dirt' line).

[Selfsim]

Logical approach, logical questions with logical answers....

.. with accompanying and many 'inconvenient' consequences noticeably missing from the argument.

Eg: Those which would purport to answer to questions such as:
"Why is there no macro evidence of higher life-forms .. which, (as per Evolution), are a logical consequence of microbial populations?"

If Astrobiology draws upon Earth's mainstream biological theories, then what is the justification for overlooking the comprehensive view in its entirety, of the variously invoked theories (like Evolution)?

Is this 'cherry-picking' by a stream of supposedly 'mainstream science'?

[Colin Robinson]

Thus, Evolution is inevitable .. it is 'intrinsic' to how living systems develop over geological timespans.

Evolution may indeed be intrinsic in the sense that living things anywhere undergo random mutation and natural selection; and they both adapt to their environments and change their environments. But why would that mean similar outcomes on different planets, especially planets with different geological histories?

According to the Mars Ocean hypothesis, early Mars would have had a thicker atmosphere to allow liquid water on the surface and would have been fairly similar to Earth's. Given that large complex organisms developed comparatively rapidly here on Earth,

The Earth is 4.6 billion years old. It has had multicellular life for about 1 billion years. You call that comparatively rapid?

there seems to have been opportunities for the same to have have happened on Mars, given an extant microbe population, (and given present theory on Mars' geological history .. which is now based on on-site geological evidence gathered by the rovers).

Except that the Mars ocean hypothesis is about Mars some 3.8 billion years ago...

[Selfsim]

Evolution may indeed be intrinsic in the sense that living things anywhere undergo random mutation and natural selection; and they both adapt to their environments and change their environments. But why would that mean similar outcomes on different planets, especially planets with different geological histories?

The Earth is 4.6 billion years old. It has had multicellular life for about 1 billion years. You call that comparatively rapid?

Not all changes are solely due to externally imposed environmental conditions.
Anyway, it depends (again) on how 'similar outcomes' is defined. What I've said in this conversation, requires accepting that the transition to multicellularity is a relatively easy step in evolutionary terms. It happened in at least 25 different species groups in Earth's past, it has been recreated in the lab, and from Earth's fossil record, it appears to have occurred inside a period of less than about 500 million years.

Absence of visible macro-scale multicellular lifeforms on Mars, (or their remnants in a previous life-favoring habit), is a data point worthy of deliberation and requires some kind of explanation. Where is it? What is it?

Except that the Mars ocean hypothesis is about Mars some 3.8 billion years ago...

.. and so?

[ASTRO BOY]

Thus, Evolution is inevitable .. it is 'intrinsic' to how living systems develop over geological timespans.

Evolution is inevitable and intrinsic as long as cosmological circumstances as well as local environmental issues allow.
You seem to be missing certain relevant points.
Mars underwent great changes....you know that.
All evidence so far suggests that the planet was once apparently far more habitable than it is at this time.
But if bacterial/microbrial life did/does exist on the planet, the early changes with regards to its magnetosphere and atmosphere would have most likely inhibited the inevitability of evolution no matter how intrinsic.

[ASTRO BOY]

Absence of visible macro-scale multicellular lifeforms on Mars, (or their remnants in a previous life-favoring habit), is a data point worthy of deliberation and requires some kind of explanation. Where is it? What is it?

.. and so?

Rapid environmental atmospheric and geological changes shortly after the advent of microbrial/bacterial life and all that it would entail.

[FarmMarsNow]

Don't laugh, but is there any chance that Earth bacteria or Earth life may have somehow infected Mars millions or billions of years ago? For instance if a very large asteroid smashed into Earth, could it have dispersed some bacteria or other life into space, been picked up by or blown to Mars?

[Selfsim]

Earth underwent rapid environmental and atmospheric changes in the past, including one which wiped out almost all extant anaerobic species of the time. And at least there's geophysical and fossil record evidence of that. Yet, multicellularity, larger and predatorial species was 'no problem' from thereon, in spite of such upheavals.

The planetary gas escape rates from both Mars and Earth are somewhat controversial. (There is evidence for both having about the same rates at present and other evidence suggesting that solar events cause more rapid erosion of Mars'). The upcoming MAVEN mission might produce more hard data on that front. The comparison pathway, (Earth vs Mars), has too many gaps to form a solid basis for solid theory development.

At the moment, the 'planetary upheaval' story in Mars' instance is just that .. a story. Until some evidence is found of ancient extant microbial martians, it is a redundant story and certainly not mainstream evidenced-based science. The mainstream answer to my query is 'unknown'. If Levin is right about Viking's results, then as Curiosity has found a once life-habitable environment at Gale crater, fossil evidence of ancient microbial activity should be present there, if life ever emerged on Mars. It is more than capable of detecting it, too. If it finds none, then 'The Story' is unsupported by the evidence it requires .. ie: evidence of extant ancient life which was co-incident with warmness and wetness. It requires this in order for it to gain any credibility legs.

[Selfsim]

Don't laugh, but is there any chance that Earth bacteria or Earth life may have somehow infected Mars millions or billions of years ago? For instance if a very large asteroid smashed into Earth, could it have dispersed some bacteria or other life into space, been picked up by or blown to Mars?

The 'chance' you mention is entirely dependent on finding evidence of past life on Mars in the first place. Without that evidence, the answer to your question is moot.

[Colin Robinson]

Not all changes are solely due to externally imposed environmental conditions.

Who said they were?

Anyway, it depends (again) on how 'similar outcomes' is defined. What I've said in this conversation, requires accepting that the transition to multicellularity is a relatively easy step in evolutionary terms. It happened in at least 25 different species groups in Earth's past, it has been recreated in the lab, and from Earth's fossil record, it appears to have occurred inside a period of less than about 500 million years.

When and how was the transition to multicellularity "recreated in the lab"?

In any case, that transition happened in nature around 3 billion years after life on Earth got started. Whether or not it was a easy step when it happened, it was a comparatively late step in the overall history of evolution.

Emergence of the first, microscopic eucaryotes was a highly significant step in evolution that came about a billion years earlier than multicellular life, but around 2 billion years after the first living cells.

Except that the Mars ocean hypothesis is about Mars some 3.8 billion years ago...

.. and so?

So, it was long before multicellular life appeared here on Earth. If evolution on early Mars was running parallel with evolution on early Earth, as your argument supposes, then there would not have been time for multicellular forms to develop.

[Colin Robinson]

Don't laugh, but is there any chance that Earth bacteria or Earth life may have somehow infected Mars millions or billions of years ago? For instance if a very large asteroid smashed into Earth, could it have dispersed some bacteria or other life into space, been picked up by or blown to Mars?

Yes, some scientific modeling has been done which suggests there is a chance of this sort of thing happening.

An earlier thread on this topic, which gives titles of some relevant books and articles.

Protozoan panspermia

[Selfsim]

Who said they were?

I did.

The point being, that the outcomes of evolving martian life, doesn't have to fit into Earth's evolutionary timeframes. In a generalised model, the relationships between external environmental factors are only one part of a very complex (and largely incomplete) 'equation'. The initial starting conditions are another .. as are a myriad of other factors. Certain macro model life features, (according to the hypotheses being pursued), are actually part of the definition applied to 'life'. These would persist in spite of some environmental changes, and terminate because of others. There is no certainty in arguing from a purely crudely known, crudely resolved geophysical Earth-centric theory, about the changes in detailed features which could (in theory) could 'tip' in any direction.

As it turns out, multicellularity does have lab evidence supporting its sensitivities to external environmental changes. This much is known .. and it can easily happen quickly .. and it has to follow unicellularity. In this case, the key generalised function creating the pressure to evolve to multicellularity is co-operation in a resource competitive, gravity based environment, which is pretty much a fundamental feature in any evolving 'life' colony (by definition and in evidence).

When and how was the transition to multicellularity "recreated in the lab"?

Ratcliff et al, announced PNAS January 2012.
Quick snapshot article here.

In any case, that transition happened in nature around 3 billion years after life on Earth got started. Whether or not it was a easy step when it happened, it was a comparatively late step in the overall history of evolution.

The life 'transition' steps usually lack the fine precision needed, (in this case), for comparative purposes (Earth vs Mars). I find this to be another reason for interpreting most of what we hear about to be a fairly rubbery 'story' (which is as good as anything as far as research pursuit is concerned, mind you .. and that's not my point here).
The lab evidence paints a finer degree of detail, temporal resolution, environmental sensitivities, and hence affords a better theoretical explanation than a purely, largely incomplete crude, low resolution, fossil/geophysical evidence record.

Emergence of the first, microscopic eucaryotes was a highly significant step in evolution that came about a billion years earlier than multicellular life, but around 2 billion years after the first living cells.
...
So, it was long before multicellular life appeared here on Earth. If evolution on early Mars was running parallel with evolution on early Earth, as your argument supposes, then there would not have been time for multicellular forms to develop.

From the linked article ..

An evolutionary transition that took several billion years to occur in nature has happened in a laboratory, and it needed just 60 days.

Then from the paper's co-author …

The new study suggests that environmental conditions are paramount: Give single-celled organisms reason to go multicellular, and they will.

Then from the paper itself ...

Although known transitions to complex multicellularity, with clearly differentiated cell types, occurred over millions of years (9, 33), we have shown that the first crucial steps in the transition from unicellularity to multicellularity can evolve remarkably quickly under appropriate selective conditions.

A rapid martian multicellularity development phase would have left adequate time for macro scale fossil evidence, (provided unicellularity happened in the first place).

I see no reasons for discarding this 'possibility' .. do you?

Also .. if martian microbes are thought to exist underground today, then they should be accompanied by multicellular (complex, larger), lifeforms which leave evidence brought to the surface by impactors, volcanoes etc.
Microbes and macro fossils go hand-in-hand. Where one exists, one expects to find the other.

[ASTRO BOY]

A rapid martian multicellularity development phase would have left adequate time for macro scale fossil evidence, (provided unicellularity happened in the first place).

I see no reasons for discarding this 'possibility' .. do you?

Also .. if martian microbes are thought to exist underground today, then they should be accompanied by multicellular (complex, larger), lifeforms which leave evidence brought to the surface by impactors, volcanoes etc.
Microbes and macro fossils go hand-in-hand. Where one exists, one expects to find the other.

So the conclusions you draw from your assumptions are that single cell life does not exist nor has it ever existed on Mars?
......I don't believe we know enough about Mars, It's early atmospheric content, the salinity or otherwise of any liquid water and its early tetonic geography and the time frame of each to reach any firm conclusion.


I do believe [as apparently do many in the related discipline] that simple cell life may have existed in the past and maybe still do based on the evidence that far better conditions did exist in the past, long enough to support such simple life, but unfavourable for anything more complex apparently.

[Colin Robinson]

As it turns out, multicellularity does have lab evidence supporting its sensitivities to external environmental changes. This much is known .. and it can easily happen quickly .. and it has to follow unicellularity. In this case, the key generalised function creating the pressure to evolve to multicellularity is co-operation in a resource competitive, gravity based environment, which is pretty much a fundamental feature in any evolving 'life' colony (by definition and in evidence).

Ratcliff et al, announced PNAS January 2012.
Quick snapshot article here.

Thank you for these references, Selfsim.

The organism used in the experiment is a species of yeast. For a bit of background, let's look at what Wikipedia says about yeasts in general.

Yeasts are unicellular, although some species with yeast forms may become multicellular through the formation of a string of connected budding cells known as pseudohyphae, or false hyphae, as seen in most molds.

Ratcliff's paper in fact mentions (on page 2) that one of the yeast species which can form pseudo-hyphae is the very species used in the experiment, Saccharomyces cerevisiae. The paper explains how the snowflake clusters produced in the experiment differ from pseudo-hyphae.

So, Ratcliff et al have not brought about evolution from a strictly unicellular species to a multicellular one. Rather, they have taken a species that is usually unicellular, but is also known to form comparatively simple multicellular structures (the pseudo-hyphae), and they have induced that species to form a different sort of multicellular structure (the snowflake cluster).

It's a very interesting result.

But does it prove that any planet with unicellular life is certain to have multicellular species as well?

I don't think so.

[Selfsim]

So the conclusions you draw from your assumptions are that single cell life does not exist nor has it ever existed on Mars?

No.
There is no need for any conclusion.

......I don't believe we know enough about Mars, It's early atmospheric content, the salinity or otherwise of any liquid water and its early tetonic geography and the time frame of each to reach any firm conclusion.

Agreed.
.. Therefore talk of microbes and sending test equipment specifically designed for that 'possibility' is premature, as there are other equally valid interpretations, (some even supported by lab based empirical evidence).

This was all learned decades ago .. from Viking's misguided ambiguous LR tests and yet some still cling to the belief that microbial life exists (and was detected) there.

Fascinating!

I do believe [as apparently do many in the related discipline] that simple cell life may have existed in the past and maybe still do based on the evidence that far better conditions did exist in the past, long enough to support such simple life, but unfavourable for anything more complex apparently.

A belief!
.. (And not the mainstream science position).

[Selfsim]

But does it prove that any planet with unicellular life is certain to have multicellular species as well?

Proof only happens with direct evidence .. and in this case, we presently have an absence of evidence, (unless one is a 'Levinist'), and a lab demonstrated 'contingent predication' (from theory).

What we are discussing is the implications on speculation, of the key principles of Earthly theories (which guide us). Those theories cannot be taken as 'proof' of anything, nor do their 'predictions' constitute anything 'mainstream'.

[Don J]

No.
.. Therefore talk talk of microbes and sending test equipment specifically designed for that 'possibility' is premature, as there are other equally valid interpretations, (some even supported by lab based empirical evidence).

Do you have any links about those empirical evidence tested in laboratory which produce the same results detected by the LR on Mars?

This was all learned decades ago .. from Viking's misguided ambiguous LR tests and yet some still cling to the belief that microbial life exists (and was detected) there.

Fascinating!

The reason for the ambiguity was caused by an another instrument which was uncorrectly calibrated. The instrument is called the GCMS and was conceived by another team of scientists.

The sensitivity of the GCMS instrument was eight order of magnitude lower than the LR.... The GCMS even frequently obtained negative results with live soils on Earth.
See page 5 and 6 of the PDF paper
http://www.gillevin.com/Mars/THE_VIK...FE_ON_MARS.pdf

To resume, the sensitivity of GCMS on Viking was set to detect organic content "in the kinds of soils you might have in your backyard or in arable land."but totally unable to detect organic content "in samples taken from Antarctica and from Siberia with active life that had the organic content of a few million cells per gram."

[Don J]

Proof only happens with direct evidence .. and in this case, we presently have an absence of evidence, (unless one is a 'Levinist'), and a lab demonstrated 'contingent predication' (from theory).

What we are discussing is the implications on speculation, of the key principles of Earthly theories (which guide us). Those theories cannot be taken as 'proof' of anything, nor do their 'predictions' constitute anything 'mainstream'.

The Likelihood of Methane-producing Microbes on Mars....
............
European Space agency article
http://www.esa.int/Our_Activities/Sp...rs_a_new_clue2

ESA PR 51-2004. Recent analyses of ESA’s Mars Express data reveal that concentrations of water vapour and methane in the atmosphere of Mars significantly overlap.

This result, from data obtained by the Planetary Fourier Spectrometer (PFS), gives a boost to understanding of geological and atmospheric processes on Mars, and provides important new hints to evaluate the hypothesis of present life on the Red Planet.

Levin's about that discovery:
http://www.gillevin.com/Mars/SPIE_Miller__CH4_2010.pdf

[Selfsim]

Don J;

Feel free to continue campaigning for a second attempt at life detection. (Same for Levin).

I personally feel very little motivation for repeating experiments which have already returned inconclusive results (regardless of the reasons and explanations for that).

The strategy which motivated the experiments in the first place was fundamentally flawed, (and still persists), so I feel great reticence when it comes to supporting a repeat mission. The idea of detecting something to 'prove' someone's speculative fantasy, seems akin to the hunt for the Holy Grail.

If life turns up whilst exploring the planet, then so much the better.
If it exists there, I feel pretty confident it'll be noticed.

[Colin Robinson]

If life turns up whilst exploring the planet, then so much the better.
If it exists there, I feel pretty confident it'll be noticed.

Not surprised you feel confident. After all, you wrote in your earlier posting...

Microbes and macro fossils go hand-in-hand. Where one exists, one expects to find the other.

In which case we can work out whether microbes are about without using a mass spectrometer, or a microscope, or even a magnifying glass.

It's just a matter of checking the sky-line for brontosaurus bones sticking out of the sand.

[ASTRO BOY]

.. Therefore talk of microbes and sending test equipment specifically designed for that 'possibility' is premature, as there are other equally valid interpretations, (some even supported by lab based empirical evidence).

The only way to get an answer to the possibility of life to ever have existed is to send test equipment. That will then give us some extra validity one way or the other and possibily support or invalidate other interpretations.
Sitting on ones hands achieves nothing.

This was all learned decades ago .. from Viking's misguided ambiguous LR tests and yet some still cling to the belief that microbial life exists (and was detected) there.

Viking's reported findings were an interpretation which underwent peer review, plus even if that result was conclusive in the negative, certainly does not mean that microbrial life could not have, or had not existed somewhere on Mars sometime.......

.. (And not the mainstream science position).

I don't believe we have a firm mainstream position on whether life did or did not exist at one time on Mars.
The question is still undecided with plenty standing with the affirmative position.
The evidence for past milder conditions on Mars, is also evidence also for the possible likelyhood of microbrial life.