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Paul Wally
2013-Jun-23, 07:09 PM
If we want to find lots of complex organic carbon compounds on Mars then where and how should we look for it?
What would be the most likely places or types of places where organics could have been preserved for billions of
years? Some ideas are polar ice caps, permafrost ice, clay deposits etc. Complex organics were found in Martian meteorites, so surely
they must be hidden somewhere. It's just a question of where and how to look for it.

Selfsim
2013-Jun-23, 09:10 PM
If we want to find lots of complex organic carbon compounds on Mars then where and how should we look for it?
What would be the most likely places or types of places where organics could have been preserved for billions of
years? Some ideas are polar ice caps, permafrost ice, clay deposits etc. Complex organics were found in Martian meteorites, so surely
they must be hidden somewhere. It's just a question of where and how to look for it.1) In a crater, where there was once water, but has been dry for a long time.
2) In clay soils. Clays preserve some organics.
3) Up to a couple of metres deep.

Just because some meteorites have been found containing non-terrestrial carbon compounds, is no guarantee that the 'lots of complex organic carbon compounds' you refer to, exists, or ever existed on Mars.

Selfsim
2013-Jun-24, 07:11 AM
Amino acids can be preserved for geologically long periods, (billions of years), in sulfate mineral matrices.

The cold, dry polar sub-soils, could serve as a cryo-preservation habitat.

The abundances of organic particles however, would be anyone's guess.

Past global dust storms, transporting airborne organic particles, could relocate them to quite unexpected areas which, whilst not particularly conducive to complex chemistry (and hence molecular 'development'), may act to preserve them from degradation by inhibiting prolonged exposures to liquid water, UV and oxidation, followiing their formation/deposition.

Selfsim
2013-Jun-24, 09:58 AM
Any present or past geothermal systems might be of interest, too.

Alluvial fans, or delta systems, where water may have once moved sediments, is another geological feature to look for.

The phyllosilicate smectites, (just like the John Klein sample) interact strongly with organics, too.

Come to think of it, the John Klein site should've been a very high probability site, according to terrestrial geological predictions ... but alas .. none were detected there ...

Paul Wally
2013-Jun-25, 10:31 PM
Come to think of it, the John Klein site should've been a very high probability site, according to terrestrial geological predictions ... but alas .. none were detected there ...

Remember, there's still the perchlorate issue. The chlorinated hydrocarbons form in a reaction during heating.

Selfsim
2013-Jun-26, 11:45 PM
Remember, there's still the perchlorate issue. The chlorinated hydrocarbons form in a reaction during heating.I concur with the underlined part. Where the reactants come from in the first place, is partially known. The contaminant, MTBSTFA, mixed in with with extant soil perchlorates, fully accounts for all of the chlorinated hydrocarbons detected.

Extant soil organics are a prediction. No such organics have yet been distinguished.
(I wish they'd announce the Cumberland drilling results .. and get on with some wet chemistry and carbon isotope testing!...)

Paul Wally
2013-Jul-06, 12:35 PM
I think this topic has many more interesting possibilities than the Viking-MSL 'stalemate' situation. So I want to present an extension
to the OP introduction.

Let's take as starting premises the following assumptions:
1) Large amounts of organics were delivered through meteoric influx to the surface of Mars in the distant past.
2) When Mars was still wetter and warmer there existed physical and chemical processes that affected the distributions, concentrations and compositions of these organic materials across the planet.

Now, given these starting premises, let's propose two possibilities about the processing of the organics:

Either, abiogenesis happened on Mars during the warmer period or it didn't happen at all. If it did happen then those organisms would have affected the distribution, concentration and composition of organics on the surface in some way that is reminiscent of life. However, if abiogenesis never happened, then the organics would have been processed in different ways leading to a different present time distribution, concentration etc. So this is the question I'm really interested in. That is, how would organic distribution, concentration and compositions on Mars differ between the two scenarios, one with abiogenesis and the other with no abiogenesis? Also, what should the search strategy be, given these two completely different scenarios?

Selfsim
2013-Jul-07, 01:49 AM
... So this is the question I'm really interested in. That is, how would organic distribution, concentration and compositions on Mars differ between the two scenarios, one with abiogenesis and the other with no abiogenesis?If LAWKI evolved, it would've 'followed the (liquid) water'. As the water evaporated and escaped, (and life retreated), the organic molecular constituents of that (surface dwelling?) life, would've broken down into smaller molecules, which would probably not be any more distinguishable today, than its presumed meteoric origin forebears, (perhaps with the exceptions of leaving more persistent artefacts of its physical existence, and maybe leaving distinguishable carbon isotopic signatures?) Its present-day adapted produce, (extinctions aside), would still be hangin' out near any traces of liquid water.

Also, what should the search strategy be, given these two completely different scenarios?The same as the one presently being pursued, (as I outlined in my previous posts).
Ie: I would say that the 'thought experiment' makes no difference to the search strategy, with the possible exception of any 'wild imaginings' the mind brings to bear, when envisaging evolved martians(?)

Don J
2013-Jul-07, 03:22 AM
I concur with the underlined part. Where the reactants come from in the first place, is partially known. The contaminant, MTBSTFA, mixed in with with extant soil perchlorates, fully accounts for all of the chlorinated hydrocarbons detected.


However we know that the MTBSTFA is not the cause of the chlorinated hydrocarbons ie (byproduct of combusted organics compounds) detected by the GCMS on Viking 1 and 2 separated by 4,000 miles apart.Also remember that the Curiosity scientists team don't reject the possibility of the presence of indigenous Martian carbon in the sample analysed by SAM.

Selfsim
2013-Jul-07, 04:01 AM
However we know that the MTBSTFA is not the cause of the chlorinated hydrocarbons ie (byproduct of combusted organics compounds) detected by the GCMS on Viking 1 and 2 separated by 4,000 miles apart.Also remember that the Curiosity scientists team don't reject the possibility of the presence of indigenous Martian carbon in the sample analysed by SAM.I concur.
It should also be noted that Viking chlorohydrocarbons had a 37Cl/35Cl ratio, which was similar to those found on Earth, and thus terrestrial contamination could still have been at cause in the Viking case, and cannot be completely ruled out. (Admittedly, these compounds were not detected at such levels in the Viking blank runs .. but these blank runs also did not cover the sample retrieval scoop etc technology, ultimately used to retrieve the actual Viking samples).

Independent confirmation of extant martian organics (and the extant 37Cl/35Cl ratios), is still required for verification purposes.

Don J
2013-Jul-07, 05:36 AM
I concur.
It should also be noted that Viking chlorohydrocarbons had a 37Cl/35Cl ratio, which was similar to those found on Earth, and thus terrestrial contamination could still have been at cause in the Viking case, and cannot be completely ruled out. (Admittedly, these compounds were not detected at such levels in the Viking blank runs .. but these blank runs also did not cover the sample retrieval scoop etc technology, ultimately used to retrieve the actual Viking samples).

Knowing that the Viking probes were submitted to a very high level of cleaning and sterilisation protocol(which unfortunately was not the case for Curiosity) it is very unlikely that terrestrial contamination be in cause.

Selfsim
2013-Jul-07, 09:21 AM
Y'know .. coming back to Paul Wally's line of enquiry, doing a deliberate 'rotation', and pondering some more, I'm starting to think that the history of how perchlorates evolved on Mars, may well turn out to be a very significant piece of this puzzle. More specifically, this could be even more focused on how chlorine evolved on Mars.

See, elemental chlorine has been detected at similar levels in every soil analyzed on Mars, and orbital measurements, (Gamma Ray Spectrometer (GRS) - Mars Odyssey), show that chlorine is globally distributed at more or less similar levels. Surely the presence and abundance of perchlorates, is an indicator of past climates and of liquid water at specific locations? It would determine ph levels and 'liquidness' at those locations, and thus ultimately, the 'usability' of liquid water for perhaps, abiogenesis(?) Whilst mineral 'signatures' might be good for general characterisation of climates and local geologies, the more briney-like, ('chloriney-like'), environments would seem to have more significance to specifically, pre-biotic and extant life chemistries, (if they ever got underway there)?

DonJ: The enrichment of 13C in CO2 released by the Rocknest sample, also doesn't help the case for soil based organics, (past or present), I might add. And that 'case' doesn't care whether the sample was close to the surface, or not. Such enrichment is indicative of inorganic, geological processes only ... not organic ones.

Paul Wally
2013-Jul-07, 04:10 PM
If LAWKI evolved, it would've 'followed the (liquid) water'. As the water evaporated and escaped, (and life retreated), the organic molecular constituents of that (surface dwelling?) life, would've broken down into smaller molecules, which would probably not be any more distinguishable today, than its presumed meteoric origin forebears, (perhaps with the exceptions of leaving more persistent artefacts of its physical existence, and maybe leaving distinguishable carbon isotopic signatures?) Its present-day adapted produce, (extinctions aside), would still be hangin' out near any traces of liquid water.


Suppose that if there were lifeforms that they migrated underground, or that whatever lifeforms were already underground just continued to evolve to the present day. But suppose there were no lifeforms to begin with, then what difference will it make to the underground scenario? Can life take the organics with them, so to speak?


Y'know .. coming back to Paul Wally's line of enquiry, doing a deliberate 'rotation', and pondering some more, I'm starting to think that the history of how perchlorates evolved on Mars, may well turn out to be a very significant piece of this puzzle. More specifically, this could be even more focused on how chlorine evolved on Mars.

The perchlorates could just be a present time, (post-warm- and- wet Mars), phenomenon. Within an ancient lake or sea there would have been all sorts of ions and maybe the perchlorate salts only formed during the evaporation period from the previously dissolved ions.

Selfsim
2013-Jul-07, 10:27 PM
Suppose that if there were lifeforms that they migrated underground, or that whatever lifeforms were already underground just continued to evolve to the present day. But suppose there were no lifeforms to begin with, then what difference will it make to the underground scenario? Can life take the organics with them, so to speak? (i) If life ever existed on the surface, I can't see how it could leave no visible traces of its existence there. Life creates and modifies its habitat. It also multiplies over much shorter timescales than geological ones. There would have to be evidence of past abundances in present day, especially as we know there have been no extensive periods of continuous water erosion (only relatively brief (geological) ones).

(ii) There is an hypothesis that life on Earth may have evolved underground first .. feeding off primordial energy laden hydrocarbons (Gold's Deep Hot Biosphere). It might be possible that it never made it to the surface, although that's a bit difficult to swallow, given the evidence of volcanism and impactors. There's also continuous, readily usable energy available at the surface (solar radiation).

iii) If no life evolved, then geological and atmospheric processes would dominate. The Tissint meteorite is presently hypothesised to have cycled back underground for a period, so I'd think organics would have been caught up in similar processes(?) In the absence of present-day life evidence, I'd think the distribution of organics circulated in this way in past, would probably look different from what abundant life would do with such organics, but there is no data to make such assessments on this yet.


The perchlorates could just be a present time, (post-warm- and- wet Mars), phenomenon. Within an ancient lake or sea there would have been all sorts of ions and maybe the perchlorate salts only formed during the evaporation period from the previously dissolved ions.There are two main hypotheses about perchlorate formation on Mars. One is atmospheric formation through gas phase oxidation of chlorine to perchloric acid, and the other formation on the surface by UV photoxidation of chlorides aided by mineral catalysts. Both would result in the global distribution of perchlorates, although localised concentrations in the right spots, I would think, would preserve water as a liquid there.
(As an aside: present detections do not distinguish between the two models - no matter how much McKay etal want us to believe that the terrestrial Antarctican and Atacama UV photoxidation process, is the dominant process on Mars).

Whilst both of these model mechanisms suggest global distributions, if the climate has changed over time, the perchlorate distributions in rocks of different ages should tell a different story. (This might be similar to the rock minerals history, but I think its more relevant to life, because perchlorates actively participate in the preservation of water in its liquid phase).

Don J
2013-Jul-08, 04:20 AM
(i) If life ever existed on the surface, I can't see how it could leave no visible traces of its existence there.Life creates and modifies its habitat. It also multiplies over much shorter timescales than geological ones. There would have to be evidence of past abundances in present day, especially as we know there have been no extensive periods of continuous water erosion (only relatively brief (geological) ones).


Global dust storm(s) on Mars can be the reason...
http://science1.nasa.gov/science-news/science-at-nasa/2001/ast11oct_2/

Selfsim
2013-Jul-08, 04:53 AM
Global dust storm(s) on Mars maybe be the reason...
http://science1.nasa.gov/science-news/science-at-nasa/2001/ast11oct_2/Nice try! :) It doesn't seem to result in major coverage of small surface rocks there though if life was clinging to some of those rocks. we'd be seeing it in the layers of ex-stream-bedrock being drilled through .. or in cross sections, where these are exposed by fractures (and in the layered sedimentary structures .. like the slopes of Mt Sharp). (Same with our Martian meteorites).

Just gotta record the following words, and ponder the differences between Martian and Terrestrial processes, and why such triggers form which can have such planet-wide impacts on such a seemingly 'inactive' planet, eh? ...
"What we have learned is that this is not a single, continuing storm, but rather a planet-wide series of events that were triggered in and around the Hellas basin," says Mike Malin of Malin Space Science Systems, Inc., lead investigator for the MOC. "What began as a local event stimulated separate storms many thousands of kilometers away. We saw the effects propagate very rapidly across the equator -- something quite unheard of in previous experience -- and move with the Southern Hemisphere jet stream to the east."

I'd be inclined to think these storms are significant factors which must distribute lighter materials evenly across the surface, though. Just recently they found bacteria from Asia floating across the Pacific and landing on the North American coast (http://phys.org/news/2012-12-plumes-pacific-thousands-microbial-species.html)
"It's a small world. Global wind circulation can move Earth's smallest types of life to just about anywhere," Smith said. It's been estimated that about 7.1 million tons (64 teragrams) of aerosols dust, pollutants and other atmospheric particles, including microorganisms cross the Pacific each year.So, from that, I would assume the Rocknest drift to be a typical sample, indicative of what we'd expect to find anywhere else where there was a pile of martian surface dirt, eh? (No significant organics, needless to say, of course).

Paul Wally
2013-Jul-12, 03:23 PM
(i) If life ever existed on the surface, I can't see how it could leave no visible traces of its existence there. Life creates and modifies its habitat. It also multiplies over much shorter timescales than geological ones. There would have to be evidence of past abundances in present day, especially as we know there have been no extensive periods of continuous water erosion (only relatively brief (geological) ones).

Who says there are no traces of its existence on Mars. Maybe we haven't been looking in the right places. If life was limited only to certain aquatic environments, then one would not expect it to have spread everywhere on the planet if there was too little time for it to have spread beyond oceans/lakes.



(ii) There is an hypothesis that life on Earth may have evolved underground first .. feeding off primordial energy laden hydrocarbons (Gold's Deep Hot Biosphere). It might be possible that it never made it to the surface, although that's a bit difficult to swallow, given the evidence of volcanism and impactors. There's also continuous, readily usable energy available at the surface (solar radiation).

Interesting, but life could also have started inside surface water environment and spread from there to subsurface water environments.




Global dust storm(s) on Mars can be the reason...
http://science1.nasa.gov/science-news/science-at-nasa/2001/ast11oct_2/

Yes, wind and volcanism have been the dominant geological processes on Mars for billions of years. Liquid water was only important in the distant past.


Nice try! :) It doesn't seem to result in major coverage of small surface rocks there though … if life was clinging to some of those rocks. we'd be seeing it in the layers of ex-stream-bedrock being drilled through .. or in cross sections, where these are exposed by fractures (and in the layered sedimentary structures .. like the slopes of Mt Sharp). (Same with our Martian meteorites).

What do you mean by 'seeing it'? It might not be that easy. I think it more likely that life would leave certain structures behind rather than actual organics, for example something like carbonate formations.

Selfsim
2013-Jul-14, 09:01 AM
Who says there are no traces of its existence on Mars. Maybe we haven't been looking in the right places. If life was limited only to certain aquatic environments, then one would not expect it to have spread everywhere on the planet if there was too little time for it to have spread beyond oceans/lakes. So you are assuming that it started in oceans/lakes? If so, there are currents in oceans and circulation in lakes which might spread it. There is evidence of free flowing liquid water in the areas currently being examined by Curiosity (and Opportunity, I believe?) .. I would think both would be in just the right places to observe evidence of the remnants of past life. The type of life is presumed to be microbial. Microbial extremophiles leave behind structural evidence like stomatolites (like in Shark Bay, WA), and visibly coloured layers atypical of the immediately surrounding sediment layers in sedimentary rock cross-sections .. (even when they're no longer living).


Interesting, but life could also have started inside surface water environment and spread from there to subsurface water environments. Maybe ... (On Earth, I don't think this can be easily determined anymore ...)


Yes, wind and volcanism have been the dominant geological processes on Mars for billions of years. Liquid water was only important in the distant past. I wouldn't discount ablation and sublimation of solid CO2 (dry ice) and mixtures involving water. This really seems to carve up a landscape, and can easily move things quite large distances ...


What do you mean by 'seeing it'? It might not be that easy. I think it more likely that life would leave certain structures behind rather than actual organics, for example something like carbonate formations.Fossilised organics can still be visible to the naked eye (and cameras). Curiosity illuminates samples with UV and other coloured LEDs to detect bio-flourescence, etc.

neilzero
2013-Jul-14, 10:52 AM
I think that surface water on Mars would move toward the core as the core of Mars cooled over billions of years, so perhaps much of the evidence is now 100 kilometers below the surface? Neil

Selfsim
2013-Jul-14, 08:58 PM
I think that surface water on Mars would move toward the core as the core of Mars cooled over billions of years, so perhaps much of the evidence is now 100 kilometers below the surface? NeilThe composition of Mars' interior is still a puzzle .. yet to be solved. It could still be a liquid. That might set a different limit to the depth for liquid water

There should be more data on atmospheric escape rates, once MAVEN starts doin' its thing.

They're also working on the liquid interior question, too (laser ranging is the latest technology for figuring that one out).

Don J
2013-Jul-15, 04:05 AM
So you are assuming that it started in oceans/lakes? If so, there are currents in oceans and circulation in lakes which might spread it. There is evidence of free flowing liquid water in the areas currently being examined by Curiosity (and Opportunity, I believe?) .. I would think both would be in just the right places to observe evidence of the remnants of past life. The type of life is presumed to be microbial. Microbial extremophiles leave behind structural evidence like stomatolites (like in Shark Bay, WA), and visibly coloured layers atypical of the immediately surrounding sediment layers in sedimentary rock cross-sections .. (even when they're no longer living).


Possible organosedimentary structure on Mars
Published in 2009 by
International Journal of Astrobiology 8 (4) : 267–280 (2009) Printed in the United Kingdom doi:10.1017/S1473550409990152 - Cambridge University Press 2009 267
http://www.pianetamarte.net/V_Rizzo_Life_on_Mars.htm
Abstract


Abstract - This study, using the Microscopic Imager (MI) of NASA Rover Exploration Mission’s (REM) ‘Opportunity’, aims to explain the origin of laminated sediments lying at Meridiani Planum of Mars, and of the strange spherules, known as blueberries, about which several hypotheses have been formulated. To this purpose, images of the sedimentary textures of layers and fragments captured by REM have been analysed; sediments that NASA has already established as ‘pertinent to water presence’. Our study shows that such laminated sediments and the spherules they contain could be organosedimentary structures, probably produced by microorganisms. The laminated structures are characterized by a sequence of a thin pair of layers, which have the features of skeletal/agglutinated laminae and whose basic constituents are made by a partition of septa and vacuoles radially arranged around a central one. The growth of these supposed organosedimentary masses is based on the ‘built flexibility’ of such a basal element; it may be a coalescing microfossil formed by progressive film accretion (calcimicrobe), in a variety of geometrical gross forms, such as a repeated couplet sequence of laminae or domal mass and large composite polycentric spherule, both in elevation. The acquired structural and textural data seem to be consistent with the existence of life on Mars and could explain an origin of sediments at Meridiani Planum similar to that of terrestrial stromatolites. The Martian deposits, probably produced by cyanobacterial activity, and the embedded blueberries could represent a recurrent and multiform product of colonies with sheath forms, resembling in shape those of the fossil genus Archaeosphaeroides (stromatolites of Fig Tree, South Africa).

Received 11 June 2009, accepted 24 June 2009, first published online 28 August 2009 Key words: blueberries, calcimicrobes, cyanobacteria, life, Mars, stromatolites.

Details and images:
http://www.pianetamarte.net/V_Rizzo_Life_on_Mars.htm

Paul Wally
2013-Jul-16, 01:50 PM
Possible organosedimentary structure on Mars

Thanks for that. Interesting stuff, and lots of references there that I would like to follow up on.
These structures might have been produced by living organisms but that does not necessarily mean we should find
organics in it, right?

Don J
2013-Jul-16, 07:12 PM
Thanks for that. Interesting stuff, and lots of references there that I would like to follow up on.

You're welcome!


These structures might have been produced by living organisms but that does not necessarily mean we should find
organics in it, right?

Right!I have started a new thread for discussions about that study.
Here:
http://cosmoquest.org/forum/showthread.php?145270-Possible-organosedimentary-structures-on-Mars

Paul Wally
2013-Jul-20, 01:35 PM
So you are assuming that it started in oceans/lakes?

I'm not assuming anything. Just trying to look at the implications of the hypothesis that life started in Martian lakes/oceans.


If so, there are currents in oceans and circulation in lakes which might spread it.

I doubt whether Mars had oceans in the same sense that we have the Atlantic ocean on Earth. Maybe there were some scattered lakes or perhaps more something like a large wetland (without the reeds of course).



There is evidence of free flowing liquid water in the areas currently being examined by Curiosity (and Opportunity, I believe?) .. I would think both would be in just the right places to observe evidence of the remnants of past life. The type of life is presumed to be microbial. Microbial extremophiles leave behind structural evidence like stomatolites (like in Shark Bay, WA), and visibly coloured layers atypical of the immediately surrounding sediment layers in sedimentary rock cross-sections .. (even when they're no longer living).

I don't know about finding fossils in free flowing water environments. Scientists seem to be more interested in sedimentary deposits like lake beds, deltas and alluvial fans, but they are less interested in river canyons. There's probably a good reason for that. Look at Gusev crater. Apparently a river flowed into the crater from the south. In Gale Crater there is a dry river canyon coming in from the north.

Given the difficulty of finding fossil evidence from 3.5Bya on Earth, I don't think it will be easy to find such evidence on Mars dating back to 3.5Bya, if it exists.


I think that surface water on Mars would move toward the core as the core of Mars cooled over billions of years, so perhaps much of the evidence is now 100 kilometers below the surface? Neil

If the gully formations observed by HiRise are really water outflows and not carbon dioxide, then the liquid water might not be as deep as 100km.

Paul Wally
2013-Jul-25, 03:50 PM
Something to consider is the notion of a carbon cycle (http://en.wikipedia.org/wiki/Carbon_cycle) on Mars (past or present). How would such a cycle or lack thereof affect the distribution of carbon containing compounds? We know for instance that water can be a carbon sink, with or without any biological agents. So surely if there were lakes or oceans on Mars, we should at least see more carbonate than what we've seen thus far.

Selfsim
2013-Jul-26, 06:56 AM
... So surely if there were lakes or oceans on Mars, we should at least see more carbonate than what we've seen thus far.Carbonates on Mars .. (http://en.wikipedia.org/wiki/Carbonates_on_Mars)

The absence of more extensive carbonate deposits on Mars was thought to be due to global dominance of low pH aqueous environments. Even the least soluble carbonate, siderite (FeCO3), precipitates only at a pH greater than 5.

Evidence for significant quantities of carbonate deposits on the surface began to increase in 2008 when the TEGA and WCL experiments on the 2007 Phoenix Mars lander found between 35wt% calcite (CaCO3) and an alkaline soil. In 2010 analyses by the Mars Exploration Rover Spirit, identified outcrops rich in magnesium-iron carbonate (1634 wt%) in the Columbia Hills of Gusev crater, most likely precipitated from carbonate-bearing solutions under hydrothermal conditions at near-neutral pH in association with volcanic activity during the Noachian era.
After Spirit Rover stopped working scientists studied old data from the Miniature Thermal Emission Spectrometer, or Mini-TES and confirmed the presence of large amounts of carbonate-rich rocks, which means that regions of the planet may have once harbored water. The carbonates were discovered in an outcrop of rocks called "Comanche."

Carbonates (calcium or iron carbonates) were discovered in a crater on the rim of Huygens Crater, located in the Iapygia quadrangle. The impact on the rim exposed material that had been dug up from the impact that created Huygens. These minerals represent evidence that Mars once was had a thicker carbon dioxide atmosphere with abundant moisture. These kind of carbonates only form when there is a lot of water. They were found with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter. Earlier, the instrument had detected clay minerals. The carbonates were found near the clay minerals. Both of these minerals form in wet environments. It is supposed that billions of years age Mars was much warmer and wetter. At that time, carbonates would have formed from water and the carbon dioxide-rich amosphere. Later the deposits of carbonate would have been buried. The double impact has now exposed the minerals. Earth has vast carbonate deposits in the form of limestone.

Paul Wally
2013-Aug-07, 09:07 PM
Carbonates on Mars .. (http://en.wikipedia.org/wiki/Carbonates_on_Mars)

Didn't curiosity also find pH neutral conditions with the first drill sampling?

I wonder if there are many examples of carbonate deposits on Earth that are not of biological origin. Such examples would be interesting
just for comparison to Martian conditions.