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Thread: Planets With Oxygen Donít Necessarily Have Life

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    Planets With Oxygen Donít Necessarily Have Life

    A cautionary tale for future research. But it is also interesting that various conditions can produce chemicals necessary for life to form.

    From Laboratory Equipment magazine

    In their search for life in solar systems near and far, researchers have often accepted the presence of oxygen in a planet's atmosphere as the surest sign that life may be present there. A new Johns Hopkins study, however, recommends a reconsideration of that rule of thumb.

    Simulating in the lab the atmospheres of planets beyond the solar system, researchers successfully created both organic compounds and oxygen, absent of life.

    The findings, published Dec. 11 by the journal ACS Earth and Space Chemistry, serve as a cautionary tale for researchers who suggest the presence of oxygen and organics on distant worlds is evidence of life there.

    "Our experiments produced oxygen and organic molecules that could serve as the building blocks of life in the lab, proving that the presence of both doesn't definitively indicate life," said Chao He, assistant research scientist in the Johns Hopkins University Department of Earth and Planetary Sciences and the study's first author. "Researchers need to more carefully consider how these molecules are produced."
    The researchers tested nine different gas mixtures, consistent with predictions for super-Earth and mini-Neptune type exoplanet atmospheres; such exoplanets are the most abundant type of planet in our Milky Way galaxy. Each mixture had a specific composition of gases such as carbon dioxide, water, ammonia, and methane, and each was heated at temperatures ranging from about 80 to 700 degrees Fahrenheit.

    He and the team allowed each gas mixture to flow into the PHAZER setup and then exposed the mixture to one of two types of energy, meant to mimic energy that triggers chemical reactions in planetary atmospheres: plasma from an alternating current glow discharge or light from an ultraviolet lamp.

    ...

    After running the experiments continuously for three days, corresponding to the amount of time gas would be exposed to energy sources in space, the researchers measured and identified resulting gasses with a mass spectrometer, an instrument that sorts chemical substances by their mass to charge ratio.

    The research team found multiple scenarios that produced both oxygen and organic molecules that could build sugars and amino acids—raw materials for which life could begin—such as formaldehyde and hydrogen cyanide.
    ACS Earth & Space Chemistry

    Abstract:
    Photochemistry induced by stellar UV flux should produce haze particles in exoplanet atmospheres. Recent observations indicate that haze and/or cloud layers exist in the atmospheres of exoplanets. However, photochemical processes in exoplanetary atmospheres remain largely unknown. We performed laboratory experiments with the PHAZER chamber to simulate haze formation in a range of exoplanet atmospheres (hydrogen-rich, water-rich, and carbon dioxide-rich at 300, 400, and 600 K), and observed the gas phase compositional change (the destruction of the initial gas and the formation of new gas species) during these experiments with mass spectrometer. The mass spectra reveal that distinct chemical processes happen in the experiments as a function of different initial gas mixture and different energy sources (plasma or UV photons). We find that organic gas products and O2 are photochemically generated in the experiments, demonstrating that photochemical production is one of the abiotic sources for these potential biosignatures. Multiple simulated atmospheres produce organics and O2 simultaneously, which suggests that even the copresence of organics and O2 could be a false positive biosignature. From the gas phase composition changes, we identify potential precursors (C2H2, HCN, CH2NH, HCHO, etc.) for haze formation, among which complex reactions can take place and produce larger molecules. Our laboratory results indicate that complex atmospheric photochemistry can happen in diverse exoplanet atmospheres and lead to the formation of new gas products and haze particles, including compounds (O2 and organics) that could be falsely identified as biosignatures.
    Last edited by Swift; 2019-Jan-02 at 06:13 PM. Reason: typo
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    Swift. Interesting chemistry. There are additional scenarios, too, from visiting molecular clouds. The Earth sits in its orbit around the sun in the Local Bubble, a giant irregular shaped relatively low density semi-void, that allows some ultraviolet observations of fellow bubble stars. Most of the void is thought to have been generated by multiple type 2 supernovae from the large stars in the OB Centaurus-Scorpio Association over the last tens of millions of years. Evidence of this is in the long -lived Fe- 60 radioisotope, found in benthic marine sediments, in multiple strata.
    Models of type 2 eject clouds indicate some molecules creating predominantly dust ( silicates, aluminum oxide), while a small abundance of molecules eventually cool in the gas phase, around a 1000 days out. Amongst them is diatomaceous oxygen. As there is also hydrogen in type 2's ejecta, water will also form. Hot hydrogen will not reduce alumina, or silicates.
    So, like Chicken Little, the Earth passing through one of the ejecta clouds, would have dusty air, and a boost in its atmospheric oxygen levels, even without green plants splitting primordial water.
    See:
    http://articles.adsabs.harvard.edu/c...IF&classic=YES

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    Didn't we know this already? Saturn's rings have an oxygen atmosphere, as do several of the larger icy gas giant moons. Complex organic photochemistry has been seen in many icy objects, and in a dense nitrogen atmosphere on Titan.

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    I'd expect many ocean worlds to have dense oxygen atmospheres, if
    a/ the planet was light enough to allow hydrogen escape and
    b/ the rocky crust was buried deep enough under a layer of high-pressure, sea-bottom ice.
    These two circumstances would mean oxygen could build up from photolysis, but it would have nowhere to go. The ice layer would prevent oxygen entering the crust and forming oxides.

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    Does there have to be ice? Could just deep water do it?
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    Quote Originally Posted by Tom Mazanec View Post
    Does there have to be ice? Could just deep water do it?
    Assuming the water is not deep enough to cover the rocks with "hot ice", oxygen dissolved in the liquid water could still be carried down to the ocean floor.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    After hydrogen and helium, oxygen's the most common element in the universe by a significant fraction. I'd expect there to be water worlds (or hot ice giants) that started with enough water to eventually fully oxidize their crust and generate an oxygen atmosphere. Couldn't say if there's been enough time for this to have happened though.

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    That was diatomic oxygen in post #2....AI changed it. Doh!

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    Even on an ocean world with an ice mantle, there might be volcanism on the bottom of the ocean that could expose reduced minerals to the water layer. This 'hot cryovolcanism' could result in an ocean floor covered in minerals that would oxidise and which might then get buried by some sort of subduction, removing oxygen from the atmosphere. But this could be a slow process on some, or many, worlds.

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    To get Oxygen in an atmosphere you need life. There are plenty of ways to get rid of oxygen, it is so reactive, but those bacteria are essential, or their living equivalent, to release oxygen gas. I should have added that chemical routes to Oxygen also reverse out into oxides, just as splitting water gives the gases necessary for later recombination. I am therefore surprised not by Hopkins analysis but the conclusion.
    Last edited by profloater; 2020-Aug-06 at 11:02 AM.
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    A world hostile to extant life is what is needed for life to evolve to begin with. A planet with too easy of a development may look inviting yet be sterile.

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    Quote Originally Posted by profloater View Post
    To get Oxygen in an atmosphere you need life. There are plenty of ways to get rid of oxygen, it is so reactive, but those bacteria are essential, or their living equivalent, to release oxygen gas. I should have added that chemical routes to Oxygen also reverse out into oxides, just as splitting water gives the gases necessary for later recombination. I am therefore surprised not by Hopkins analysis but the conclusion.
    No, you don't need life to have an oxygen rich atmosphere. If a planet has a lot of water on its surface that water can evaporate, become water vapour then be split by sunlight (star light) and lose the hydrogen because it is light enough to escape. If there is enough water on the surface of the planet this can prevent oxidation, so the water will remain in the atmosphere.

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    Like some of the others, I'm a bit surprised that anyone did think planets with oxygen necessarily had life.
    A: "Things that are equal to the same are equal to each other"
    B: "The two sides of this triangle are things that are equal to the same"
    C: "If A and B are true, Z must be true"
    D: "If A and B and C are true, Z must be true"
    E: "If A and B and C and D are true, Z must be true"

    Therefore, Z: "The two sides of this triangle are equal to each other"

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    Quote Originally Posted by profloater View Post
    To get Oxygen in an atmosphere you need life. There are plenty of ways to get rid of oxygen, it is so reactive, but those bacteria are essential, or their living equivalent, to release oxygen gas.
    Free oxygen on Earth is largely produced biologically, but that's a method of doing so. It doesn't make it the only method possible.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Well I agree that there are routes to Oxygen but they have been demonstrated as traces. Hydrogen or methane etc will readily recombine with Oxygen at a few percent. The early bacteria had he ability to proliferate and use energy to release Oxygen without flammable hydrocarbons. Has it been shown that a water planet can produce more than trace oxygen? That would be interesting to learn about.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    We haven't made any close observations of water planets yet, unless you count Neptune and Uranus, which are often described as ice giants. Both Neptune and Uranus are big enough to retain hydrogen, and cold enough that photolysis of water rarely happens. But there seem to be many, many planets that have characteristics between those of Earth and those of Neptune. Some of these will probably be ocean planets. And of those, some will probably have oxygen-rich atmospheres.

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    I see upon checking references that the proportion of Earth Oxygen due to dissociation has been steadily revised upwards by research, so the escape of hydrogen from Earth sized planets is feasible as a non biological route to significant percentages, so i am grateful to be corrected.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    So, if oxygen breathers are put on oxygen rich worlds with no biosphere to replenish things, what would be the result?
    Lots of oxygen gives us a head start, but plants?

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    Well, on a planet with no biosphere, the first thing we would run out of is food. For a planet like Earth, there is far more oxygen than we need, so we would not suffocate. The oxygen content of the atmosphere is far larger than the biomass on Earth, so even if the entire biosphere died and was burnt into carbon dioxide, there would still be almost the same amount of oxygen left.

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    That is good to know.

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    One question is, what else would a non-biotic atmosphere have besides oxygen? There's a lot of stuff that most aerobic life can't breathe. Do biological processes remove toxins from an atmosphere (besides CO2)?
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Toxin is a relative term. Life forms either derive energy from chemistry or use energy such as light, to do chemistry. So there are anaerobic bacteria and aerobic with us today. They can extract Nitrogen, which is quite a trick , and break down most compounds given time (to evolve). They do it for their own “purposes” while we might see some chemicals as toxins. Of course bacteria also can make what to us are toxins.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    Quote Originally Posted by profloater View Post
    Toxin is a relative term. Life forms either derive energy from chemistry or use energy such as light, to do chemistry. So there are anaerobic bacteria and aerobic with us today. They can extract Nitrogen, which is quite a trick , and break down most compounds given time (to evolve). They do it for their own “purposes” while we might see some chemicals as toxins. Of course bacteria also can make what to us are toxins.
    Yes, but not my point.

    The atmosphere we have now has oxygen, nitrogen, a little CO2, and "trace gasses". Those gasses were once much more than a trace. So how did they get reduced? Was it through biological activity?
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Well I guess not, combustable gases and vapours get oxidised, or dissolve in water and fall down. So gases like H2S, SO2 or 3 do not need biology even though some bacteria can use them. Most biology takes place in the water or at the surface so true gases would escape. The usual traces, I think are escaping H and He, some CO (also light) .
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    So there could conceivably be a planet with a human-breathable atmosphere and no native biology?
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    I'm fairly sure that this could happen. Nitrogen is an atmophile element, and would probably exist as an atmospheric gas on a lot of planets. Oxygen could occur on some planets where water vapour can be split by the action of sunshine, and where hydrogen can escape relatively easily. Other atmospheric gases, like argon, neon, even helium, might exist in some quantity but not affect the breathability much, because they are inert and non-toxic.

    But some common atmospheric gases could be toxic. Carbon dioxide can be deadly in high concentrations, so can nitrous oxides, carbon monoxide, ammonia, and so on. Just because oxygen is present doesn't mean you would be comfortable.

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    Quote Originally Posted by eburacum45 View Post
    But some common atmospheric gases could be toxic. Carbon dioxide can be deadly in high concentrations, so can nitrous oxides, carbon monoxide, ammonia, and so on. J
    So what could reduce those gasses in an atmosphere without biological life? I know carbon can be absorbed into the crust up to a point.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    So what could reduce those gasses in an atmosphere without biological life? I know carbon can be absorbed into the crust up to a point.
    I assume you mean reduce in the sense of decreasing them. I think the issue itself is very complex, and depends on the actual situation, but chemical reactions do not require biology. For example, on the earth, a very toxic gas released by volcanoes H2S, is oxidized and therefore changed to sulfur and water which, I think, precipitate. But of course, you need O2, which is a biological product. There are also gases that will either rise in the atmosphere.


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    Quote Originally Posted by Jens View Post
    But of course, you need O2, which is a biological product.
    The whole point of this thread is non-biological sources of free oxygen!
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    One question is, what else would a non-biotic atmosphere have besides oxygen? There's a lot of stuff that most aerobic life can't breathe.
    I thought you were asking another question, and was trying to help with that. I realized that the the original question was about oxygen, which is why I put in the disclaimer, but I thought you wanted to know how toxins could be eliminated without life. The original question was about whether the presence of oxygen indicates life, and Iím not certain how toxins relate to that question.


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