PDA

View Full Version : Methane on Mars and Earth



Colin Robinson
2012-Dec-12, 12:47 PM
(From the thread "How Small Can Life Be")


So the concentration level somehow leads to a conclusion, or a non conclusion of life existence, eh? So just how is the concentration threshold decided?

It's not a question of a "threshold".

The atmospheric concentration of methane on Mars (around 10 parts per billion) is much lower than here on Earth (around 1.7 parts per million).

I can think of two possible explanations (perhaps you can think of another?)

Either
1. Compared to Earth, Mars has methane sources (processes that produce methane) which are far less active, or
2. Compared to Earth, Mars has methane sinks (processes that turn methane into something else) which are far more active.

The 2nd explanation seems unlikely, if only because Earth has lots more dioxygen (O2) in its atmosphere, and O2 reacts exothermically with methane...

If the 1st explanation is the right one, then methane-producing organisms on Mars, if they exist at all, are far less active than those of Earth.


Chemical reactions can still occur in a system which has reached chemical equilibrium...

No doubt. Just like you still have molecules milling about in a system which has reached thermal equilibrium. But a system at thermal equilibrium does not provide the sort of energy which can power a heat engine. Can a system at chemical equilibrium provide the energy needed by living things?

Selfsim
2012-Dec-13, 01:19 AM
(From the thread "How Small Can Life Be")The other thread actually contained arguments which demonstrate the issues arising from using this test as a method for eliminating planets from consideration. The whole point of that other thread was querying whether our definition of life was of sufficient completeness to distinguish what may be deemed to be life … in our own environment.

This may be a short-lived thread (from my perspective).


It's not a question of a "threshold".It must be because …

The 2nd explanation seems unlikely, …Once again, the threshold is used as a basis for eliminating things using 'likely/unlikely' which in turn, demonstrates that there's a model assumed which somehow has rolled into it, assumptions about the relationship between a particular type of life and particular atmospheric gases.

You yourself, pointed out that oxygen can be produced in other ways .. and I'd say there may well be other ways of sustaining its presence in that atmosphere … and we'd assume 'likelihood' of life on that planet/moon, because of it?


The atmospheric concentration of methane on Mars (around 10 parts per billion) is much lower than here on Earth (around 1.7 parts per million).

I can think of two possible explanations (perhaps you can think of another?)

Either
1. Compared to Earth, Mars has methane sources (processes that produce methane) which are far less active, or
2. Compared to Earth, Mars has methane sinks (processes that turn methane into something else) which are far more active.

The 2nd explanation seems unlikely, if only because Earth has lots more dioxygen (O2) in its atmosphere, and O2 reacts exothermically with methane...

If the 1st explanation is the right one, then methane-producing organisms on Mars, if they exist at all, are far less active than those of Earth.Its all compared back to an Earth-life/metabolic by-product model .. and that's the issue .. we have no idea as to whether that model is sufficiently generalised to be regarded as 'universally' applicable or not. That hypothesis is the matter under test. Its universal applicability is assumed, before the full tests are complete. In contrast with this approach, are the 15 or so detailed tests, outllned in the other thread, which were needed to eliminate uncertainties here, on Earth at the molecular level. These tests used a different basis for eliminating uncertainties, which doesn't assume universality of the model under test. That such extensive tests are needed here on Earth, to characterise a terrestrial discovery, demonstrates just how inaccurate the assumptions really are, about exo-gases and life. The key assumption above, is that remote exo-gas sensing is suitable for this purpose. It demands a model which has not been shown to be applicable anywhere else, other than Earth. This is now bringing assumptions pertinent to a hypothesis into empirical testing, and then applying a subjective judgement to the results, in order to eliminate other 'possibilities' which were the very subject of the initial hypothesis. It uses that hypothesised model, and an opinion about 'likelihood/unlikelihood', as the basis for doing so. Can you see how biased a conclusion that will lead to?

Its also completely circular rationale.

Oh, and what about the 'Mars-life is underground' hypothesis? (Ie: your 'type 2', above). What if the hypothesised methane produced, is localised and isolated, and never actually makes it into the atmosphere? (Sequestered). Why should that be dismissed as 'unlikely' with so much surface ice being present?


No doubt. Just like you still have molecules milling about in a system which has reached thermal equilibrium. But a system at thermal equilibrium does not provide the sort of energy which can power a heat engine. Can a system at chemical equilibrium provide the energy needed by living things?Maybe. Depends on how long it stays in that phase (and how often). (What happens during McKay's favoured 'dormancy' phase?) What if the sample under test turns out to be a molecular scale lifeform making use of something else as its energy source, which results in an extremely slow metabolism? Slower metabolisms in different chemical environments, might have completely different energy needs … (not just the one you're looking to draw inferences from).

…………………………….

And what about Earth-life's own (hypothesised) barely post-biotic anaerobic geological phase? Would such an exo-environment be deemed an 'unlikely' environment for hosting exo-life, according to inferences being drawn from this test?

Also, what if, for eg, Mars' surface perchlorates are actually used for metabolism, following say an inorganic reaction, which manages to release sufficient oxygen, which is then consumed before it makes it into the atmosphere? Perhaps the reaction just looks like chemical equilibrium from a remote sensing POV, because it is (a) sub-surface or, (b) extremely slow or, ( c) cyclical and unobserved as being so?

We don't know how specific our ideas about life are. The generalisation of it, may be based on assumptions which may not be valid to generalise from. This is what is under test. The remote exo-gas sensing method, does not result in sufficiently constrained uncertainty, so as to enable elimination of many other generalised considerations .. it doesn't even come close to it.

Colin Robinson
2012-Dec-13, 09:32 PM
The other thread actually contained arguments which demonstrate the issues arising from using this test as a method for eliminating planets from consideration.

It is not a question of eliminating planets from consideration, but of giving consideration to the evidence we have.

Given that mainstream scientists consider methane detected on Mars to be relevant as a possible product of organisms there, is it not also relevant to note that the level of that possible product is very, very low in comparison to products of life in the atmosphere of Earth?


Its all compared back to an Earth-life/metabolic by-product model .. and that's the issue .. we have no idea as to whether that model is sufficiently generalised to be regarded as 'universally' applicable or not.

No discussion of life in the universe can ignore life on Earth, because right now it is the only instance we have.

The question to consider is which characteristics of life on Earth are historically specific (e.g. because they result from chance mutations), which characteristics are adaptations to conditions on this particular planet, and which if any characteristics are general to life anywhere (e.g. because they are due to general principles of physics and chemistry which are not specific to Earth)?

In order to grow, repair and replicate, life needs an energy source. As far as I'm aware, no scientist doubts this proposition, which (if I remember correctly) you, Selfsim have agreed with in other threads. The reason they don't doubt it, is that it derives from basic principles of thermodynamics, which apply on other planets too.

Life needs an energy gradient, it needs the possibility of energy flow. That is, it needs non-equilibrium conditions...


Also, what if, for eg, Mars' surface perchlorates are actually used for metabolism, following say an inorganic reaction, which manages to release sufficient oxygen, which is then consumed before it makes it into the atmosphere?

Yes, using perchlorate to oxidize something would be a thermodynamically possible way of getting energy, provided there are substances that can be oxidized and that yield energy when they are oxidized. If organisms did that, they would change the composition of their environment in ways that could be modeled and tested for by planetary scientists.

Selfsim
2012-Dec-14, 04:38 AM
It is not a question of eliminating planets from consideration, but of giving consideration to the evidence we have.

Given that mainstream scientists consider methane detected on Mars to be relevant as a possible product of organisms there, is it not also relevant to note that the level of that possible product is very, very low in comparison to products of life in the atmosphere of Earth? Ok … I propose a halfway meeting, Colin … (ie: I get your point):

I think the finality in what you said below, represented something slightly different to what you're saying in this thread:

If you accept that chemistry is a necessary part of life, surely it follows that Mars is "dead or almost dead"?Chemistry, (or organic reactions described by the Laws of Chemistry), whilst certainly being necessary for life, is by no means sufficient to explain its presence, or absence.

The specificity of the model needed to interpret remote exo-gas measurements, is what the search for exo-life is enquiring into. I don't see how we can make assumptions about that, and then use them in order to reach a definitive conclusion following the test, (like 'dead', or even 'almost 'dead'). A null result, when methane is present, doesn't say anything about your 'other possibilities', (and admittedly, a 'dead' planet may also be amongst those).


No discussion of life in the universe can ignore life on Earth, because right now it is the only instance we have. Which forms part of the model basis, (which is incomplete), of the hypothesis under test. Its ubiquity throughout the universe, is unknown.


The question to consider is which characteristics of life on Earth are historically specific (e.g. because they result from chance mutations), which characteristics are adaptations to conditions on this particular planet, and which if any characteristics are general to life anywhere (e.g. because they are due to general principles of physics and chemistry which are not specific to Earth)?No .. the answer to your latter question is: "unknown".

If we think we have a generalised definition of life which might be found anywhere, then we cannot use assumptions in that model, to exclude other 'possible' instances of it in advance of any discovery. (..Or attempt to minimise/maximise perceptions of instances of it, using inference based terms like 'likely/unlikely', etc). The model will be iteratively changed because it is presently an approximation, and it will change to accommodate variations .. but that can only happen once a discovery is made, ET tells us about his atmospheric gases, some second abiogenesis is concluded on earth, or some new lifeform is made in the lab.. and this is the whole problem with the exo-gas detection approach. Either we assert a generalised model, or we limit it to being specifically about Earth-life. Its the vacillation between the two interpretations, which makes the hypothesis inconsistent, when it comes to the testing part.


In order to grow, repair and replicate, life needs an energy source. As far as I'm aware, no scientist doubts this proposition, which (if I remember correctly) you, Selfsim have agreed with in other threads. The reason they don't doubt it, is that it derives from basic principles of thermodynamics, which apply on other planets too. And I think I'm still being consistent in what I'm saying. Under the model assumed, the amounts of energy required, would be specific to the environment in which it is/has been adapting (to).


Life needs an energy gradient, it needs the possibility of energy flow. That is, it needs non-equilibrium conditions… … which doesn't have to be a steady-state equilibrium. The question then becomes one of the temporal scales over which a particular type of non-equilibrium persists .. we have no data on that, nor on the sensitivities of other hypothesised lifeforms to it.


Yes, using perchlorate to oxidize something would be a thermodynamically possible way of getting energy, provided there are substances that can be oxidized and that yield energy when they are oxidized. If organisms did that, they would change the composition of their environment in ways that could be modeled and tested for by planetary scientists.Well, maybe .. maybe not .. Those models would be purely hypothetical, and not necessarily be of any indicative (or predictive) usefulness. This in turn, depends on the data they draw upon, and the particular model assumptions.

Githyanki
2012-Dec-17, 02:25 AM
I think the Methane produced on Mars originating from micro-organisms is a great theory; I don't think there is enough evidence to support that claim as of now. Now, I do think that there is cross-planet contamination and if they're are microbes on Mars, they probably originated from Earth. I personally believe some of the methane-sources are from microbes, but I can't state it as a fact until we actually discover these microbes and prove the methane isn't from a natural geologic source.

TooMany
2012-Dec-17, 05:05 PM
I personally believe some of the methane-sources are from microbes, but I can't state it as a fact until we actually discover these microbes and prove the methane isn't from a natural geologic source.

Are there any nature geologic sources of methane (on Earth), that do not involve past or present life?

Colin Robinson
2012-Dec-17, 10:27 PM
Are there any nature geologic sources of methane (on Earth), that do not involve past or present life?

Yes, the process known as serpentinization. See the WP page serpentinite (http://en.wikipedia.org/wiki/Serpentinite).

TooMany
2012-Dec-17, 10:59 PM
Yes, the process known as serpentinization. See the WP page serpentinite (http://en.wikipedia.org/wiki/Serpentinite).

That's interesting. Looks like the process would be unlikely on Mars though (since the crust is thick and the planet has cooled and there are no moving plates). Unless there are stores from an earlier time that are slowly leaking.

If we every do find living microbes on Mars, we might be able to tell whether or not it's related to earth life even if it is quite similar to Earth life. Possible we could look at the DNA and see differences.

MaDeR
2012-Dec-18, 05:15 PM
Possible we could look at the DNA and see differences.
Assuming they have DNA at all. Some genetic code containing inheritance data, sure, but DNA like Earth life?

TooMany
2012-Dec-18, 07:43 PM
Assuming they have DNA at all. Some genetic code containing inheritance data, sure, but DNA like Earth life?

I was addressing the question "if we find life on Mars that is very similar to Earth, how can we know if it's actually alien (and not contamination from Earth)?"

There are some theorist who believe DNA is fundamental to organic life, others who don't. Who knows until we find other examples.