Did salt lick Martian life?

By Phil Plait | February 15, 2008 1:21 pm

Scientists working to see if Mars ever had life have concentrated, of course, on looking for water. It appears to have been abundant on Mars a long time ago, but what was it like?

On Earth, water can be pure, or salty, or laden with minerals and metals. On Mars, the presence of minerals like jarosite indicate that at least in some spots, Martian water was high in minerals, with a corresponding high acidity. That’s bad enough, but now evidence from the rover Opportunity indicates that the water was also very salty, far higher in salinity than Earth’s oceans.

This has dimmed somewhat the idea of life on Mars, at least lately — meaning, the last few billion years. It’s possible that the water was in better shape to develop life as we know it early on in the history of Mars, but over time, the water got more acidic and more salty. At first blush, this precludes life arising and flourishing on the Red Planet, but I wonder. One scientist said "This tightens the noose on the possibility of life," but I think that’s a hasty conclusion.

Life arose on Earth almost immediately after the asteroid and comet bombardment ceased, just a billion or so years after Earth formed. Conditions then were very different than they are now, and yet here we are. Whatever life started back then, it evolved, adapted. Every corner of the Earth has life in it, from miles down under the surface to pools of chemicals that would kill a human (and most bacteria) instantly. Check out D. radiodurans for a real eye-opener on how tough life can be. I have little doubt our oceans have changed their salinity numerous times over the past 3 billion years, and life adapted.

From this press release, it’s impossible to say how much things have changed on Mars — besides, of course, the loss of its atmosphere, its water, and the drop in temperature. In this case, I mean how the water on Mars changed over time, and how rapidly. If it happened overnight, then sure, it’s not hard to imagine it wiping out all life on the planet. But what if it took, say, a few million years? Life on Earth has survived horrific circumstances in the past. Could any possible Martian life have done the same?

We still have no idea if life ever arose on Mars or not — Mars cooled more rapidly than the Earth did, and so may have had life on it before we did. If any life did form there, it may not be around anymore, and there could be any number of causes. We simply don’t know, and I think it’s way too early in our exploration of the planet to rule anything out.

Comments (41)

  1. Salty water?

    If we sent probes to Death Valley, what would they determine about the character of Earth’s now-dead oceans? These are smart people, and I’m sure they’ve considered that oceans/seas/lakes concentrate minerals as they evaporate, but I haven’t seen that mentioned yet. What would a fresh water lake leave behind?

  2. wright

    Hear, hear BA. We’ve only seen tiny pieces of Mars in any detail, meaning close-up “hands on” (albeit remotely) examination. An awful lot of rocks that still need to be turned over. Literally.

    And as enormous a thing as it would be to find that there is or was life there, Mars is fascinating (to me at least) even without it. That frakking huge lava cave or whatever it is, evidence of water flowing very recently, the seasonal variations in the polar regions. And that’s just the stuff we are finding out at the beginning!

    We need more robots there; rolling, peering and prying into all the places they can go. And humans, if we can possibly get there and back, doing all the things we do so much better (so far) than robots.

  3. > “it’s impossible to say how much things have changed on Mars — besides, of course, the loss of its atmosphere”

    I assume you mean it lost some of its atmosphere, rather than all of it?

  4. There may well have been life on early Mars, but I would be extremely surprised if there is any there now. Consider the surface conditions: mean global annual surface temperature 214 K (water freezes at 273 K). Mean surface pressure 636 pascals (compare to 101,325 Pa on Earth). Atmosphere: 95.32% carbon dioxide, 2.7% nitrogen, 1.6% argon. No ozone layer, so a surface saturated by solar ultraviolet light. Violent dust storms that churn the surface material, exposing all of it to the ultraviolet over time. The likely presence of superoxides in the soil.

    It’s possible that there are small niche environments in which Martian life has survived — under the polar ice caps, maybe, or deep in the regolith. But I wouldn’t hold my breath.

  5. Michelle

    What I wonder is… how do you MAKE life? I mean, I know there’s elements and all, but what do you need to make a cell or bacteria or whatever was the first lifeform ever? Did we ever take stuff and create our own lifeforms from scratch?

    …Maybe I’m thinking too much.

  6. Chip

    Extremophiles on Earth can live is very salty water with high mineral content but perhaps the assumption is that earliest life evolves out of conditions that promote the chemical reactions conducive to life forming and then life can later adapt itself to more extreme conditions. Within this growing diversity, some forms also become extinct.

    I’m hopeful that knowledge of Mars will continue to grown to the point where they can identify possible ancient environmental niches.

  7. andy

    Well given that life on this planet managed to cope with the environment getting flooded with that notorious and highly corrosive toxin oxygen, is hypersalinity all that big a problem?

  8. dusty59

    Yeah, and nothing could possibly live in radiation, boiling or freezing water, highly acidic environments……
    blah blah blah blah.
    What Jeff, Chip and others say above- don’t underestimate the capabilities of life.

  9. The press release doesn’t say how salty the oceans of Mars supposedly got – and as far as I’m concerned, a press release that doesn’t include a number is by definition a non-story, and a bad day for science PR – but here’s a paper that says Earth’s precambrian oceans were twice as salty as they are now:

    http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6R-4F4NYHS-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=d17b18e69eef609f591968a4f71f818c

    Here’s something talking about microbes that live in saltwater 10x more saline than seawater:

    http://www.genomenewsnetwork.org/articles/2004/02/20/antartic_microbes.php

    And here’s some comments about a microbe found a few years ago with salt concentrations inside its cell wall that are up to 20x that of seawater:

    http://www.genomenewsnetwork.org/articles/08_03/hottest.shtml

    “That means there is very little free water present in these bugs. This could stabilize DNA and many of the other molecules in the cells and may be a key to their survival.”

    Huh. So extremely salty conditions could be good for life. Meanwhile we’ve got some PR hack translating someone’s scientific findings into “too briny for life.” There’s only so much salt you can put into water without taking special steps to supersaturate it, so I’m not finding the claim very compelling.

  10. Justin

    Hmm…D. radiodurans…possibly the 0.01% of bacteria that Lysol doesn’t get?

    Now my question on this would be, all we know about life in the Universe is what we have on Earth. We keep looking for water as a source of life (because that is what we know.) Why could life not form that doesn’t depend on water? Why couldn’t there be life on, say, Venus that is adapted to what we call harsh conditions here?

  11. Tom Marking

    There is an interesting subgroup of extremophiles known as halophiles or “salt lovers”. These belong to the domain archaea.

    http://en.wikipedia.org/wiki/Halophile

    “Most halophiles are unable to survive outside their high-salt native environment. Indeed, many cells are so fragile that when placed in distilled water they immediately lyse from the change in osmotic conditions.”

    To each his own. To the halophiles their high salt environments are ideal and our human environment is toxic. Some of them live in solutions that are 36 percent salt. So I wouldn’t rule out life on Mars in the past based on salty oceans.

  12. Tom Marking

    “Now my question on this would be, all we know about life in the Universe is what we have on Earth. We keep looking for water as a source of life”

    Justin, there has been a lot of speculation that life might be based on a fluid substance other than water. Two often-mentioned candidates are liquid ammonia (NH3) which boils at -33 degrees Celsius and liquid methane (CH4) which boils at -162 degrees Celsius. These might be ideal compounds for planets in the outer solar system. We know there is abundant liquid methane on the surface of Titan, so who knows what Mother nature has come up with. That’s why we need a repeat of the Huygens probe as soon as possible. I think they should send a spacecraft shaped like a boat and let it splash down in one of Titan’s seas. Then we might learn something about the chances of life originating on other worlds.

  13. Justin

    @Tom Marking:
    Thanks for the answer! It just kind of annoys me when scientists condemn alien movies because the aliens are constantly hominids, and that suggests that we are only drawing from already existing knowledge, but then they turn around and say they look for water b/c that’s the only substance known to support life.

    My thinking is, if there is other life out there, who says we will even be able to recognize it as life? Perhaps I’m putting too much thought into this…

  14. A few points: We have no idea how early life evolved here on Earth, because there are basically no well-preserved surface rocks from the first 700 million years or so of Earth history.

    In contrast, much of the Martian surface is ancient, so if something was around back then, it should still be preserved.

    Thus, it is a good bet that if Mars did have early oceans, they probably didn’t host life advanced enough to do things like build huge reefs, because we can’t see any such things.

    As for this recent report, I see no mention of an associated paper, and the AAAS Boston meeting does not have abstracts online, so there is no way to see what the talk was about. So unless we know what the evidence is, it is hard to interpret the press release. However, the type of salt that they found could be just as important as the total dissolved solids.

  15. That’s it! A way to make a buck, and speed the manned exploration of Mars. Import Martian Sea Salt for the discriminating gourmet with too much money and a taste for the extraterrestrial.

  16. Radwaste

    Guys, if Mons Olympus was caused by a deep, heavy asteroid strike, would that account for the lack of atmosphere and oceans? Does a planet with little magnetic field get its atmosphere stripped by the solar wind?

  17. Big Shane

    When does the fossil hunt end and the terraforming begin? I like fossils and all, but I like crops and forests and prairies and swamps…

  18. wright

    Radwaste, the prevalent theory (to my understanding) is that Mars lost most of its volatiles gradually. A combination of the low gravity, chemical reactions that formed those lovely orange oxides, ultraviolet radiation breaking down gases and water vapor; things like that.

    It’s clear Mars has endured numerous large impacts. I believe there’s a theory that Iceland might have been created by an asteroid strike, but have no idea how much is known about the formation of Mons Olympus.

  19. Jeffersonian

    I’m optimistic. We’ve only recently, on our own planet, had a surge in discovery of extremophiles. The limits are being stretched…

  20. TheBlackCat

    Water isn’t just some liquid that our cell are full of. It is a central component of the structure of most of our proteins. Proteins fold because their free energy when folded is smaller than when not folded. This is obvious. What is far from obvious is that most of this free energy changes comes from an entropy increase not an enthalpy (thermal energy) decrease. And most of that entropy increase comes from rearranging water molecules. The only reason water molecules can only drive this large entropy change because they are polar. A non-polar solvent, like a hydrocarbon such as methane, couldn’t do it. Other polar solvents don’t have a configuration that allows for as many meta-states (which dictates how much of an entropy change they can undergo).

    Although I suppose it is possible for a simple organism to exist with a much slower metabolism that allowed for the most slower folding of biomolecules, at least on Earth the free energy difference between different folding configurations is minuscule even with such strong interactions driving it and this results in mis-folded proteins being fairly common. It would be difficult to get anywhere near even this reliability without excessive energy costs.

    It is also possible that that a form of life could exists that is isn’t even based on folded macromolecules, and that might avoid this difficult entirely. But whatever the case, it is not a matter of just taking out water and sticking in some other solvent. Water has very unique properties that not other solvent has, and those properties are essential for any life form even remotely similar to life on this planet. If it is even possible at all it would take major changes and come at a serious performance penalty.

  21. wright

    Interesting, TheBlackCat; thank you. So there might be only so many ways to make relatively complex life. Or even if there are alternatives, we might expect water-based life to be more common.

    Ideally, we need a true basis for comparison. Like finding the Martian equivalent of D. radiodurans, or freeswimming life in Europa’s hypothesized sub-ice oceans.

  22. Brian

    Add to that the fact that water is one of the most common molecules in the universe, and you understand why any idea for life that doesn’t depend on water has a lot of explaining to do up front.

  23. TheBlackCat

    Water is actually the second most common molecule (after diatomic hydrogen), and probably second by a sizable margin. Oxygen is the second most common molecule-forming element (hydrogen is first, helium is second overall but inert), over twice as common as the next, nearly 8 times more common than the one after that, and about ten or more times more common than every other. And since hydrogen is more common by over one and a half orders of magnitude than every non-inert element combined, it is a rare occurrence for elements to interact with anything but hydrogen. And since oxygen only forms one stable molecule with hydrogen, while the next most common carbon forms a nearly unlimited number, we are looking at water being the second most common by a large margin (although of course diatomic hydrogen beats it out by a much larger margin).

  24. KaiYves

    Licking… why so many posts about licking recently?

  25. TheBlackCat

    Do you really want to know the answer to that question?

  26. Tom Marking

    I agree that the water molecule is essential for LAWKI (Life As We Know It) but it is not entirely clear that it is essential for LAWDKI (Life As We Don’t Know It). There are a couple of points:

    1.) Ammonia (NH3) is also a polar molecule

    2.) The atmosphere of Jupiter is 0.3% methane, 0.026% ammonia, and 0.0004% water (http://en.wikipedia.org/wiki/Jupiter). Thus, methane is 750 times more abundant than water and ammonia is 65 times more abundant than water. These abundances may be more representative of what to expect since the Jovian atmosphere is thought to reflect the initial chemical composition of the original solar nebula.

    3.) Having a water molecule on a planet with a temperature below 0 deg C does not help life. Whatever the solvent, it must be liquid in the temperature range of the planet in question. So water may be the solvent of life on planets close to their stars and ammonia/methane may be the solvent for more distant planets.

    For those interested in LAWDKI I would highly recommend the book “Artificial Life: The Quest for a New Creation” by Steven Levy.

    And as always, BlackCat, it’s been a pleasure locking horns with you again. :)

  27. Will. M

    All:
    I’ve read about silicon being a substitute for carbon as a basis for life forming. Has that idea been ruled out after the latest discoveries about extremophiles on earth and the chemical makeup of many of this solar system’s planets and those of the newly discovered planets in the farther reaches of space?

  28. Tom Marking

    “I’ve read about silicon being a substitute for carbon as a basis for life forming.”

    That idea started based on the periodic table since silicon is the next element down in the column containing carbon (valence = 4). It also is quite abundant with about 28 percent (by mass) of the earth being silicon. I certainly wouldn’t rule out silicon-based life although others might, although it’s hard to imagine a planet with abundant silicon that would not also be abundant with carbon. Carbon tends to make far more compounds with other elements than silicon does, but on the other hand silicon based compounds are less volatile so perhaps on some hotter world (Mercury comes to mind) some sort of silicon-based life might be imaginable.

  29. TheBlackCat

    I agree that the water molecule is essential for LAWKI (Life As We Know It) but it is not entirely clear that it is essential for LAWDKI (Life As We Don’t Know It).

    I already said this. But any life form must follow the basic rules of chemistry. That is a fundamental requirement. If other solvents do not have the characteristics necessary to support life (which may or may not be the case) then life will not evolve in those solvents.

    Just throwing out “life as we don’t know it” is really no different than goddit. You could use that to get around any requirement we know of for life (“LAWDKI doesn’t necessarily have to be made out of matter”). Given limited resources we need to set limits somehow. The rules of chemistry indicate targeting water is the best strategy. We know water has basic chemical properties that make it particularly suitable for the promoting specific folding of complex macromolecules. No other chemical has those properties, period. That puts limits on the biochemistry of life in other solvents. Either it can get by with slower, less specific, and/or less efficient folding of macromolecules or it can avoid the use of macromolecules entirely. But it cannot do what life on Earth does with water, the rules of chemistry just doesn’t allow it.

    1.) Ammonia (NH3) is also a polar molecule

    I already dealt with this as well. It’s configuration does not lend itself to the large number of rotational and bending states that water has. It could possibly be a substitute, but it wouldn’t do the job anywhere near as well as water does.

    2.) The atmosphere of Jupiter is 0.3% methane, 0.026% ammonia, and 0.0004% water (http://en.wikipedia.org/wiki/Jupiter). Thus, methane is 750 times more abundant than water and ammonia is 65 times more abundant than water. These abundances may be more representative of what to expect since the Jovian atmosphere is thought to reflect the initial chemical composition of the original solar nebula.

    That is only water vapor, it doesn’t include water in liquid or ice form. Water vapor concentration is very low on Earth as well.

    3.) Having a water molecule on a planet with a temperature below 0 deg C does not help life. Whatever the solvent, it must be liquid in the temperature range of the planet in question. So water may be the solvent of life on planets close to their stars and ammonia/methane may be the solvent for more distant planets.

    Irrelevant, if (big if) life cannot develop or cannot develop as well without water, then if water isn’t present then either life won’t develop or it won’t develop as well.

  30. Tom Marking

    BlackCat, please provide a URL for your assertion that the water molecule is essential for the folding of large macromolecules since I have not heard of that before. Is that any macromolecule or only macromolecules found to be relevant to earthly biology? When two amino acids combine to form a dipeptide they produce an extra water molecule. I’m not sure that’s what you’re talking about when you claim water is essential for macromolecule folding.

    In general, protein folding is largely governed by certain amino acids in the chain being hydrophobic (repelled by water) which will tend to seek the interior of the protein and other amino acids being hydrophilic (attracted to water) which will tend to seek the exterior of the protein. Of course, it is the polarity of the water molecule which causes hydrophilic and hydrophobic amino acids and not the “large number of rotational and bending states” of the water molecule (whatever that’s supposed to mean). Any other molecule of similar polarity should produce similar although not identical results.

  31. TheBlackCat

    Here are some sources:
    http://mrw.interscience.wiley.com/emrw/9780470015902/els/article/a0003002/current/abstract
    http://mrw.interscience.wiley.com/emrw/9780470015902/els/article/a0002975/current/abstract
    http://www.rsc.org/Publishing/Journals/CP/article.asp?doi=b404327h

    I’m not sure that’s what you’re talking about when you claim water is essential for macromolecule folding.

    As I already explained in my first post, protein folding is dominated by entropy changes, and a large part of this entropy change comes from water molecules.

    In general, protein folding is largely governed by certain amino acids in the chain being hydrophobic (repelled by water) which will tend to seek the interior of the protein and other amino acids being hydrophilic (attracted to water) which will tend to seek the exterior of the protein.

    Only partially correct. The two main driving forces (assuming no hydrogen bonds are broken) is “hiding” hydrophobic amino acid residues from water (as you described) and the massive decrease in entropy due to the very flexible protein chain being locked into a specific conformation (reducing entropy to nearly zero). This competition between the large decrease in entropy from fixing the protein’s structure and the large increase in entropy from separating hydrophobic amino acid residues from water is what controls protein folding (or the lack thereof). The actual free energy difference between folded and non-folded proteins is actually very small because the entropy decrease from fixing the protein’s shape is so large. The free energy difference between two different folded states is smaller yet..

    Non-polar solvents do not have an entropy increase when they are separated from polar amino acids, thus there is no large free energy source that can compensate for the entropy decrease caused by folding the protein (or any other macromolecule).

    Of course, it is the polarity of the water molecule which causes hydrophilic and hydrophobic amino acids and not the “large number of rotational and bending states” of the water molecule (whatever that’s supposed to mean).

    This is a common misconception, but wrong. Hydrophobic and hydrophilic interactions are primarily due to entropy. The enthalpy loss due to losing polar interactions between water molecules is a minor issue relatively speaking. The polar nature of water is part of the reason for the inordinately high entropy of liquid water, but the shape and flexibility of water molecules play a large part as well. Nonpolar residues due not have very much entropy at all because they do not have discrete states like polar molecules do. Other polar molecules have discrete states, but nowhere near as many as water does so they also have considerably lower entropy. See my sources above.

  32. TheBlackCat

    I should add something. Not only is entropy the main driving force of hydrophobic interactions, it is actually the only positive driving force. Enthalpy actually promotes hydrophobic chemicals dissolving in water. But the entropy drop is so large that it more than overcomes this enthalpy drop and thus hydrophobic chemicals do not dissolve readily in water.

    For those who don’t know, here is a crash course in basic chemistry. Enthalpy is what people normally call the “heat” of a reaction. When you burn wood, the heat and light are from enthalpy. Entropy is a measure of the number of possible configurations a given substance can take. More configurations means more entropy. When you are looking at a process, what determines whether the process will occur (without external energy input) is the interplay between entropy and enthalpy. A decrease in enthalpy makes the process more likely to occur. A decrease in entropy makes it less likely to occur. So when I say “a large entropy drop”, this is something that is working against the process occurring. When I say “a large enthalpy drop” this is something that promotes the process occurring. Entropy is actually a major driving force in chemical interactions but not one you normally think about unless you have been specifically trained to do so. It is what allows self-chilling cold packs to work, for instance.

    Here is another resource, a book this time:

    Physical Chemistry of the Life Sciences
    Peter Atkins and Julio de Paula
    Chapter 2 (p 77-100), particularly p 95-96

  33. The low atmospheric pressure of Mars is probably due not just to its low gravity, but to “impact cratering” of the atmosphere — Mars gets a much higher flux of impactors than Earth does, and there’s some thought to the effect that a good fraction of its atmosphere may have been blown off the planet that way. Wouldn’t work with Earth, which has higher gravity.

  34. TheBlackCat

    But didn’t Earth get an impact by an object the size of mars? I thought that supposedly stripped it of most of its organic molecules and substantially changed its atmospheric makeup (besides forming the moon).

  35. Tom Marking

    “Here are some sources:
    http://mrw.interscience.wiley.com/emrw/9780470015902/els/article/a0003002/current/abstract
    http://mrw.interscience.wiley.com/emrw/9780470015902/els/article/a0002975/current/abstract
    http://www.rsc.org/Publishing/Journals/CP/article.asp?doi=b404327h

    The first two articles are pay-per-view (or free if you are a member of the web site) so I didn’t delve into them. But based on their titles they appear to be dealing exclusively with proteins in aqueous solution. The third article entitled “Entropy/enthalpy compensation …” also deals exclusively with water as a solvent. The word ammonia is not found one time in the article so there is obviously no comparison of water versus ammonia. So this is hardly convincing evidence that water is the only possible solvent for any organic macromolecule. Since there are quadrillions of possible organic macromolecules only a small fraction have ever been studied in earthly laboratories.

    I have managed to find some obvious comparisons of the two molecules however:

    http://en.wikipedia.org/wiki/Water_molecule
    Water molecule:
    bond length = 95.84 picometers
    bond angle = 104.45 degrees

    http://en.wikipedia.org/wiki/Ammonia
    Ammonia molecule:
    bond length = 101.7 picometers (6 percent more than water molecule)
    bond angle = 107.8 degrees (3 percent more than water molecule)

    http://www.ualberta.ca/~jplambec/che/data/p00403.htm
    Water:
    Delta-enthalpy of formation (DH0f) = -241.818 kJ/mole
    Delta-Gibbs energy of formation (DG0f) = -228.572 kJ/mole
    Entropy (S0) = 188.825 kJ/mole
    Heat capacity at constant pressure (C0p) = 33.577

    Ammonia:
    Delta-enthalpy of formation (DH0f) = -46.11 kJ/mole
    Delta-Gibbs energy of formation (DG0f) = -16.45 kJ/mole
    Entropy (S0) = 192.45 kJ/mole
    Heat capacity at constant pressure (C0p) = 35.06

    Thus, the entropy for ammonia is only 2 percent different than the entropy of water. Wasn’t this supposed to be the defining property of the water molecule, its supposed huge entropy? Well, ammonia’s is two percent higher. The only substantial differences between water and ammonia in terms of thermodynamic properties appears to be in their enthalpies of formation. It takes five times as much energy to break a water molecule into its constituent atoms as it does for ammonia. But since you never mentioned that particular point I don’t think its relevant to your argument.

  36. TheBlackCat

    No need to worry about entropy, the solubility of hydrophobic chemical in ammonia relative to water can be directly measured, and has been. Ammonia dissolves polar chemical well, but not as well as water, while it dissolves nonpolar chemicals poorly, but significantly better than water. This is exactly the problem I was describing.

    http://www.infoplease.com/ce6/sci/A0856597.html

  37. TheBlackCat

    And before you start arguing about the importance of entropy, I only brought it up because I knew it is a common misconception that hydrophobicity is driven by enthalpy. You need to use entropy if you start getting into a detailed quantitative analysis of protein folding (or folding of any macromolecule) but if you understand its importance then what matters for a qualitative analysis is the relative solubility in different substances.

  38. It should be remembered that there is still the evidence for earlier, less acidic (and less salty?) water, which left behind the clay mineral deposits, documented by Mars Express. Ray Arvidson of the MER team mentioned this again in this recent December 10, 2007 update:

    http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html

    “We see evidence from orbit for clay minerals under the layered sulfate materials,” said Ray Arvidson of Washington University in St. Louis, deputy principal investigator for the rovers’ science payload. “They indicate less acidic conditions. The big picture appears to be a change from a more open hydrological system, with rainfall, to more arid conditions with groundwater rising to the surface and evaporating, leaving sulfate salts behind.”

    I’ve commented about this on the blog, also.

    Paul

    The Meridiani Journal
    a chronicle of planetary exploration
    web.mac.com/meridianijournal

  39. Again, _some_ of Mars’ early water was acidic and salty, not all of it. The newest recent discovery (announced just a few weeks ago) of carbonate deposits is yet more evidence of that, as was discussed by the scientists themselves. Why can’t some people understand that what has been found by the rovers in two tiny areas cannot necessarily be extrapolated to the entire planet? The evidence from the orbiters continues to indicate a variety of conditions in the past, just like on Earth.

    Paul

    The Meridiani Journal
    a chronicle of planetary exploration
    web.me.com/meridianijournal

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