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A New Context for Complex Life

We normally think of the appearance of oxygen on Earth in terms of a ‘great oxygenation event,’ sometimes referred to as the ‘oxygen catastrophe’ or ‘great oxidation.’ Here oxygen begins to emerge in the atmosphere about 2.3 billion years ago as oceanic cyanobacteria produce oxygen by photosynthesis. The actual oxygenation event would be the point when oxygen is not all chemically captured but becomes free to escape into the atmosphere.

It’s a straightforward picture — we move from a lack of oxygen to gradual production through photosynthesis and then a concentration strong enough to destroy many anaerobic organisms, an early and huge extinction event as life on our planet adjusted to the new balance. But a team of researchers led by Michael Kipp (University of Washington) has produced a paper showing a much more complicated emergence of oxygen, one that produced a surge in oxygenation that lasted a quarter of a billion years before easing.

Kipp and team studied oxygen in the Earth’s atmosphere between 2 and 2.4 billion years ago. Their work focuses on the element selenium and its isotopic ratios in sedimentary shale, using mass spectrometry techniques at the University of Washington Isotope Geochemistry Lab. The question: How have isotopic ratios been changed by the presence of oxygen? The reduction of oxidized selenium compounds causes a shift in these ratios which can be measured, and the abundance of selenium itself increases as oxygen levels climb.

What the team found is that oxygen levels were higher far earlier than we’ve believed. Indeed, these levels may have supported complex life, at least for a time. For instead of a gradual and continuing rise, these levels then drop. Roger Buick (UW Astrobiology Program) explains:

“There is fossil evidence of complex cells that go back maybe 1 ¾ billion years. But the oldest fossil is not necessarily the oldest one that ever lived – because the chances of getting preserved as a fossil are pretty low. This research shows that there was enough oxygen in the environment to have allowed complex cells to have evolved, and to have become ecologically important, before there was fossil evidence. That doesn’t mean that they did — but they could have.”

100_0527-Schreiber-beach-Gunflint-basal-strom

Image: This is a 1.9-billion-year-old stromatolite — or mound made by microbes that lived in shallow water — called the Gunflint Formation in northern Minnesota. The environment of the oxygen “overshoot” described in research by Michael Kipp, Eva Stüeken and Roger Buick may have included this sort of oxygen-rich setting that is suitable for complex life. Credit: Eva Stüeken.

Thus shallow coastal waters may have held the oxygen needed for complex life hundreds of millions of years earlier than thought. The researchers call this event an ‘oxygen overshoot,’ a significant increase in atmospheric oxygen and in the surface ocean, but one that did not affect the deep ocean. Oxygen levels would have risen for a quarter of a billion years before sinking back. That makes the so-called ‘great oxygenation event’ a more complex process than we realized, with a sharp peak in oxygen before a drop to a lower, more stable level.

About this complex process there remain plenty of questions. What caused the elevation of oxygen levels in the first place, and what precipitated its decline? The researchers have no answer, but can only point to a selenium isotope record that clearly sets this period apart. The selenium technique is a potent way to analyze our own planet’s past, but it also reminds us of the need to be cautious in evaluating exoplanet habitability. Says lead author Kipp:

“The recognition of an interval in Earth’s distant past that may have had near-modern oxygen levels, but far different biological inhabitants, could mean that the remote detection of an oxygen-rich world is not necessarily proof of a complex biosphere.”

The paper is Kipp et al., “Selenium isotopes record extensive marine suboxia during the Great Oxidation Event,” published online by Proceedings of the National Academy of Sciences 18 January 2017 (abstract). This UW news release is also helpful.

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  • Nicolas AUGUST January 18, 2017, 11:15

    The first multicellular organisms are 2.1 billion years old and formed around that time in a rich oxygen environment.
    See: https://en.wikipedia.org/wiki/Francevillian_biota
    “The Francevillian biota (also known as Gabon macrofossils or Gabonionta) is a group of 2.1-billion-old Palaeoproterozoic, macroscopic organisms known from fossils found in Gabon.

    What is particularly interesting is this (from Wikipedia):
    “The Francevillian biota disappears and is absent in the overlying black shale. El Albani attributes this to their extinction. The biota formed with the Lomagundi event, a temporary increase in atmospheric oxygen, and became extinct from marine anoxia when the event ended”

  • Mark T. January 18, 2017, 15:26

    It is the oxygenation of planetary atmospheres sufficient for complex life to evolve that is probably the first place where the Drake equation really begins to limit the number of alien civilizations. We know there are more planets than you can shake a stick at. The number of planets in the habitable zones of their stars probably exceeds the number of stars. Furthermore, for a variety of reasons, many scientists strongly suspect bacteria are all over the galaxy. However, the difficulty Earth had establishing a stable, well-oxygenated atmosphere suggests such worlds are likely to be far less abundant. This is speculation at the moment, however, eventually we will have an abundance of exoplanet light spectra to identify exoplanet oxygen and my money is on well-oxygenated worlds in the habitable zones of their stars being very rare percentage-wise.

    • NS January 19, 2017, 5:44

      This paper (pdf) argues that life may emerge on most wet rocky planets, but unless it rapidly evolves to the point where it can stabilize its environment it soon goes extinct:

      http://adi.life/pubs/ChopraLineweaver2016.pdf

      • Ashley Baldwin January 19, 2017, 18:00

        If you want to read about the high likelihood of life arising on aqueous planets ( the authors’ term) a good read is Cohen and Stewart’s outstanding ” What does a Martian look like ? ” , their self confessed sound bite title for what is essentially. ” POLOOPA”, “Possibility OF Life On Other Planets” .

        From 2002 but incredibly prescient in the light of subsequent exoplanet science and far better than geocentric astrobiology , the creation largely of astronomers ( had it been biologists then it would have been bioastronomy ) .

        Drafted just before , but published after “Rare Earth ” which also allows for a well balanced and comprehensive rebuttal. Cohen is a retired Xeno/ biologist who for thirty years helped create full self contained alien ecosystems for Terry Prattchet , Larry Niven , Greg Bear and many other established authors of cerebral SF.

    • Michael Fidler January 19, 2017, 8:30

      But this constraint is associated whith the amount of oxygen sinks – on earth mostly iron. Since exoplanets have a varity of compositions there may be whole groups of them that do not have any major oxygen sinks.

      • Ashley Baldwin January 19, 2017, 18:10

        Spot on. Geocentricity is is alive and well.

        Astrobiogy – Astronomer created science derived from biology of the Earth superimposed on astronomic observation .

        If biology led it would have been “Bioastronomy “.

        Should really be Xenoscience.

      • Mark T. January 19, 2017, 18:37

        Michael, you may be right, but there are so many variables and unknowns here that I am finding it difficult to come to any firm conclusions both with regard to detecting such worlds in general and what that might mean for finding alien civilizations.

        One variable is just how reasonable is it to expect significant quantities of abiotic oxygen in a habitable zone planet? Was Mars an example?
        Another variable is whether abiotic oxygen will be in sufficient quantities and duration for alien civilizations to form? Yet another variable is what are the oxygen-absorbing effects of everything else besides iron? Oxygen combines with so many different things, iron cannot be the only oxygen sink. If you are right, oxygen is a poor biomarker by itself, which has also been proposed. However, if all the other factors are satisfied, then the lack of alien civilizations on such oxygenated worlds becomes an even deeper mystery. In other words, if you look at the 1,000 closest, oxygenated, habitable planets with at least 2 billions years of oxygen and ours is the only civilization, you have to wonder where the bottlenecks are. Let’s just hope that most or all of those bottlenecks are behind us.

  • Ashley Baldwin January 18, 2017, 17:35

    Nothing new about O2 not being a bone fide bio marker for complex or even non complex life. On its own anyway . Non biological O2 production is well recognised mainly through photo dissociation of H2O. Life linked to O2 according to a recent article by Barnes et al ( in the immediate aftermath of the Proxima b discovery ) suggests that the concomitant existence of the O4 molecule with O2 is more strongly suggestive of a biogenic origins of O2 ,and both can be detected remotely by spectroscopy .

    The first evidence of life on Earth dates to around 3.85 billion years ago , long before O2 existed as well. A lot of Earths history to date was during this time. How would that look on a remote spectrum of an exoplanet , even in the “habitable zone” of its star ?

    As to an initial short lived peak of O2 this would still fit with the “Snowball Earth” hypothesis . More so in fact . Despite still being debated , it has a large amount of circumstantial evidence to support it . It causes were initially and over simplistically posited as being due to the erstwhile 02 driven “Great Oxidative event/ crisis” ( whichever way you look at it ) disrupting the greenhouse gas feedback mechanism created by the inorganic carbon/silicate cycle that had effectively regulated ( and moderated ) Earth’s temperature through atmospheric CO2 levels . It has however been refined over time .

    The evidence is strongest for several times during the 500 million years of the neoproterozoic period prior to the “Cambrian explosion” but suggestions of much earlier episodes are also available. The turnover of the Earth’s crust over such long extended periods leads to reliance on much less accurate radiometric dating of the various types of related geological findings such as banded iron oxide formations ( BIFs) and planet wide glaciation, even at the equator .

    One thing is clear though, if there have indeed been such periods they have not just been related to O2 increases alone . The position of the continental mass in particular has also been linked with cooler periods due to the counter intuitively high albedo of equatorially positioned land mass versus the very low albedo of tropical seas. It’s also worth mentioning that even a “billion” years ago Sol was also 6% less luminous than today with accordingly lower values still in more remote times cited in thus article .

    Whatever the cause of a snowball Earth one thing is certain , the planet wide ice coverage would severely impact on any photosynthesis and thus O2 production and through that decimate any organisms dependent on it , including any complex life that might have evolved to utilise its high metabolic potential . ( the C13/C12 isotope ratio is a sensitive market for photosynthetic activity – don’t know if the paper mentions that ? )

    There have been numerous Snowball periods mooted during the late neoproterozoic in particular , so why not earlier too if the correct circumstances aligned ? That related to the Graet Oxidation event of 2.4-2.1 billion years ago being just the most notorious ( we also know about the variations in the Earth’s orbit that probably contributed to the much smaller scale recent “Ice ages ” on their own, but may also have played a role in earlier more cataclysmic cold episodes . ) In fact more so with a much dimmer Sun to add in to the equation even without continental changes .

    Ultimately volcanic activity would melt holes in the ice and over time restore temperate climates through its greenhouse effect , possibly further enhanced by the release of methane from deep sea clathrate deposits ( a much more potent greenhouse gas that has been implicated as warming the very early Earth to levels that allowed the initial development of life long prior to O2 production -a “reducing atmosphere ” rather than the current O2 oxidative . Until along came Cyanobacteria or whatever precursor organism that went into symbiosis with early archaean life to create them )

    The ” Snowball Earth” related extinctions of the later neoproterozoic have been implicated in creating the greater biodiversity ( akin to low level UV ) that led to the Cambrian explosion by creating a greater “phase space” for post episode life to expand into . Be interesting to see if earlier episodes had a similar effect that simply was too long ago to show up in the fossil record .

    One thing is for sure, the climate of the Earth throughout life’s long history on Earth has played a huge role in its development , possibly most recently via Ice Ages driving primates down from retreating woodland environments to exposed grassland where expending ( O2 driven ) energy through big, energetic brains was more suitable to their survival than climbing.

    • Mark T. January 18, 2017, 22:06

      Ashley, you make some great points and you obviously know a thing or two about the geological history of Earth. If you are willing to consider a question, how would the oxidation of Earth’s atmosphere be different if Earth’s atmosphere 3.85 billion years ago had the same components in the same ratios, but were ten (10) times thinker?

      • Ashley Baldwin January 19, 2017, 15:26

        A toughly ! Chicken and egg question really . Remember that life first arose on Earth within this very reducing atmosphere with its varying concentrations of presumably vulcanism realeased gases like methane and sulphur oxides . Difficult to see how the atmosphere could have been different given this with the ecosystem at that time unable to exist in isolation. Whatever life first formed did so within the confines such an ecosystem imposed and then expanded to fill it . “Phase space ” How could it not ?

        Whether or not life would have formed down a different pathway in the unlikely occurrence of atmosphere makeup you suggest is unclear .( if not Earth then on say a smaller planet with less vulcanism) . Maybe totally differently , possibly not at all. Exoplanets that followed these subtly different routes might well show what happens . The elements of terrestrial life are largely Carbon, Hydrogen, Oxygen and nitrogen ( CHON) which are fairly well the commonest available on Earth for a variety of reasons each is uniquely well suited to produce “life as we know it ” . They are also the most commonly available ( in space too where more and more of the “building blocks ” of life molecules are being discovered ) . No coincidence there then . However, there are probably many different ways they could line up to create life “as we don’t know it” . With even subtle variations of any planetary ecosystem , so it’s likely that life is probably common but very different from one planet to another.

        Everyone talks of carbon dioxide as THE greenhouse gas. However methane and water vapour are far more effective and would almost certainly have played a key role in the early Earth’s reducing atmosphere in establishing the temperate/ warm surface temperatures that engendered the type of chemical reactions that no doubt eventually gave rise to early life . No atmosphere and the Earth would have an equilibrium temperature of -30 C even with today’s Sun. How much dimmer was the sun 3.85 million years ago than now ? Greenhouse warming would thus have been even more important , indeed vital , then so you can see one way that reduced concentrations of the initial gases could have made all the difference , especially if lower . Permanent Snowball ? .

        Oxygen came along later , forming as a byproduct of photosynthesis , a useful biological adaptation that allows direct use of sunlight as a source of power . Arising on several independent times in Earth’s history as no surprise given it’s such an effective adoptive trick so would be heavily favoured by natural selection . That probably means that it could arise elsewhere even amongst entirely different ( but still CHON based ) life , making it a very potent bio marker and effective source of O2 – so one way or another making the latter a good bio marker though not just on its own .

        Shouldn’t be too long before the “red edge” created by photosynthetic absorption of specific wavelengths of visible light might be detected in planetary spectra . Or maybe a different absorption ” edge ” dependent on the wavelengths making up light from the parent star .

        O2 initially reacted with things like iron to build up chemical sinks before overcoming them and building up in the atmosphere largely as a toxin to all primitively non photosynthesising prokaryotic ( no nucleus or advanced cellular organelles ) life . Subsequent symbiosis with life that adapted to utilise oxidative metabolism (actually helping filter out toxic O2 for non utilisers initially ) probably led to more organised and complex eukaryotic life as one organism absorbed another to create cells with nuclei ( what defines eukaryotes ) and other organelles like mitochondria and chloroplasts – which in turn created new symbiosis over time to form yet more sophisticated multicellular life . Metabolically hungry life that needed the energy available from O2 and creating greenhouse CO2 as a byproduct . A biological as well the non biological (silicate weathering) related atmospheric negative feedback carbon cycle .

        Seeing life as a feature of an interrelated ecosystem rather than arising in isolation is the basic tenet of the “Gaia ” hypothesis , somewhat exaggerated ( and a bit spoilt ) by the hyperbole associated with suggesting the whole of the Earth’s ecosystem is just one big organism . Not entirely illogical mind .

        With CO2 the new thermostatic green house gas , the rest is history , interspaced with hiatus snowball Earth periods which gradually diminished over time as the Sun became brighter and the biggest continents drifted away from the equator .

        • Mark T. January 20, 2017, 18:28

          Ashley, thank you for your response. To summarize, you believe (as do I) that life would soldier on under those conditions, but adapt accordingly, i.e., expand into its available “phase space.” You wrote, “[w]ith even subtle variations of any planetary ecosystem , so it’s likely that life is probably common but very different from one planet to another.” That makes a lot of sense considering the tremendous variation here on Earth, even controlling for conditions. For example, even with convergent evolution, a puffin is different from a penguin.

          That said, and all things being equal, can you speculate on whether it would take substantially longer to oxygenate a thick atmosphere (10X Earth) as opposed to a thin atmosphere?

    • Michael Fidler January 19, 2017, 8:19

      Just wondering how these impacts could of effected the snowball earth and the GOE?pppdhttp://www.nature.com/nature/journal/v485/n7396/full/nature10967.html
      The barrage of comets and asteroids that produced many young lunar basins (craters over 300 kilometres in diameter) has frequently been called the Late Heavy Bombardment1 (LHB). Many assume the LHB ended about 3.7 to 3.8 billion years (Gyr) ago with the formation of Orientale basin2, 3. Evidence for LHB-sized blasts on Earth, however, extend into the Archaean and early Proterozoic eons, in the form of impact spherule beds: globally distributed ejecta layers created by Chicxulub-sized or larger cratering events4. At least seven spherule beds have been found that formed between 3.23 and 3.47 Gyr ago, four between 2.49 and 2.63 Gyr ago, and one between 1.7 and 2.1 Gyr ago5, 6, 7, 8, 9. Here we report that the LHB lasted much longer than previously thought, with most late impactors coming from the E belt, an extended and now largely extinct portion of the asteroid belt between 1.7 and 2.1 astronomical units from Earth. This region was destabilized by late giant planet migration10, 11, 12, 13. E-belt survivors now make up the high-inclination Hungaria asteroids14, 15. Scaling from the observed Hungaria asteroids, we find that E-belt projectiles made about ten lunar basins between 3.7 and 4.1 Gyr ago. They also produced about 15 terrestrial basins between 2.5 and 3.7 Gyr ago, as well as around 70 and four Chicxulub-sized or larger craters on the Earth and Moon, respectively, between 1.7 and 3.7 Gyr ago. These rates reproduce impact spherule bed and lunar crater constraints.

      • Ashley Baldwin January 19, 2017, 18:42

        Good question . The late heavy bombardment period occurred well before the mooted time of the GOE though and was the only time of extended and frequent impacts . Any subsequent impact events occurred as a result of normal bombardment via NEOs ( like the K/ T) seperated by long periods . Although any dust cloud caused by a large impactor could have cooled the Earth whether this was enough to cause a Snowball Earth is unlikely . There is evidence that the Earth recovered from the K/T event climatically anyway within centuries or at worst millennia ( tiny on geological scales – not so good for life short term anyway )

        As the Snowball Earth theory has been ( rightly ) challenged it has been refined and moved from having one cause ( eg GOE) to multi factorial – dim Sun, GOE, continental positioning , variations in Earth’s orbital eccentricity , obliquity , precession cycles etc . All of which need to align , thus reducing the likelihood of such a cataclysmic event , the more so as the Sun brightened progressively reducing one major risk factor permanently . In the last billion years we have nothing worse than Ice Ages ( though the continental positioning away from the equator might have helped protect too )

        This might be supported by last likely Snowball episode occurring in the neoproterozoic 1-0.5 billion yra when the Sun was still at least 6% dimmer.
        If Snowball Earth did indeed occur it’s possible there would have been impact events during such an extended period . It’s interesting to see what if any effect if any this would have had .

        My hunch is that it would have to be a large impact to have any significant effect and given even the relatively large K/T asteroid climate and planet wide effects were probably short lived , all the Snowball Earth contributory factors mentioned above would trump it and the effect minimal. If it happened Snowball Earth was a serious event in our Planet’s history – worse by far than any of the ” recent “mass extinction events. Perhaps Snowboulder Earth would be a better name. Immovable – almost. ( it has been theorised that Earth could recover from even a 99 % level extinction event though presumably over some time )

        • Michael Fidler January 21, 2017, 10:51

          Ashley, you have given me some food for thought! The Cambrian explosion developed right after the last snowball earth, so what are the possibility that more advance life forms developed above the ice. We look at the earth in it current state but we have never seen a planet in a snowball state, could volcanoes and impacts have put enough organic material on this ice for something like ice worms to develop? The fossil record from anything above the ice would have most probable been destroyed and what are the possibility of pockets that could have been conducive to the evolution. The only example we have is Antarctica, but in a word wide event there may have been many zones of weather conditions. One way to see if the Cambrian explosion developed from the lifeforms that evolved above the ice is to see if any of the fossil record at the beginning of the explosion might have characteristics related to ice worms or other arctic multicellular organisms. Interesting idea. :-}

          • Michael Fidler January 21, 2017, 22:53

            Interesting article on land life developing as far back as 2.2 Billion years ago!
            ORIGINS OF LIFE
            Early Life in Death Valley
            https://www.quantamagazine.org/20140424-early-life-in-death-valley/
            While many paleobiologists now accept Knauth’s premise that simple, unicellular life forms existed on land during the Precambrian, others recoil from his more radical proposal that complex, multicellular life — and even animal life — also thrived on land more than 600 million years ago.
            According to prevailing wisdom, the continents were lifeless, irradiated rock shelves until after the occurrence known as the Cambrian explosion in the seas 540 million years ago, when the precursors to rooting plants and animals burst forth from the ocean to colonize the land. Knauth has long led the charge to challenge that narrative, which is biased by the fossil record, he said. Marine fossils are protected by layers of marine sediment and the quietude of ocean deeps. Land fossils are much more likely to have been pulverized by changing climates and erosion long before paleontologists could have chanced upon them. The fossil record, therefore, is heavily weighted toward the seas, making it appear that they were the cradle of life.
            Gregory Retallack, a paleobotanist at the University of Oregon, and collaborators pushed back the arrival of life on land even further, reporting that land-based microfossils unearthed in South Africa could be as old as 2.2 billion years.

            • Alex Tolley January 22, 2017, 14:57

              “A petrified bedbug would end the dispute,” he said with a grin.

              The ball is in his court to find the evidence of pre-Cambrian animal life on land.

  • Coacervate January 18, 2017, 18:03

    Mars seems to have a thin veneer of oxidised minerals over a reduced substratum. How would that have formed without an O2 atm?

  • Geoffrey Hillend January 18, 2017, 18:42

    Fungi and Planets gave us the oxygen increase according to this article: http://science.psu.edu/news-and-events/2001-news/Hedges8-2001.htm

  • ole burde January 18, 2017, 18:53

    If I try to imagine the best-possible exoplanet for human settlement ,in a realistic scenario where settlers arive after a 400 year journey , it may be a world where life never happened . On a waterrich planet ,free oxygen can be created by the escape of hydrogen to space over a long time . When alle the chemical demands for oxygen are saturated , the oxygen will start to acumulate . This would demand a deep ocean to start with , but so what ?
    On a planet with native life , the imune systems of the human setlers might not be capable of recognizing the local bacteria as such , causing strange and unpleasant things to happen …or the locals could be capable of out-competing earth life in general ,while themselves indigestible to the settlers.
    In opposition to this potential disaster , a planet with an earthlike oxygen content , but without life , could probably be terraformed relatively fast if all the necessary chemicals where present .
    I short there are more than one kind of planet to hope for …

    • Mark T. January 18, 2017, 22:55

      Makes sense, but I would be willing to bet that planets like that are unbelievably rare. If life-free planets that are 100% compatible for humans even exist, it is likely the temporary result of a catastrophe bad enough to sterilize that planet, but not strip its atmosphere and oceans beyond the point we would find comfortable. I have to wonder if this is just about as likely as you finding an impeccably clean mansion with a sign on it that says, “free to the first taker.”

      • ole burde January 19, 2017, 14:16

        My main concern is to have a Plan B for spacefligt , if it should turn out that no signs of life can be found , no matter how good the technology becomes.If this should be the case , and so far there is no contradictory evidence , then we are faced with the depressing prospect of a million year long terraforming process as the only way to create an attractive destination for interstellar flight …..except if another kind of planet can be found where most of the oxygeneation has already been done by chemical proces’s : an older planet with a deep ocean , perhabs completely covered by its ocean ….

        • Alex Tolley January 19, 2017, 14:43

          What forms humanity+ will be in even 1000 years is unknown. I suspect that whatever passes for humanity that wants to go to the stars will not need terraformed planets. They may not even be biological as we think of the term.

          That isn’t to say that humanity won’t want to be “greening the galaxy”, but that bringing life to dead worlds will not be the purpose of creating human habitats.

          Terraforming may not even need much more than 10,000 years per planet, perhaps even less. Laying down biospheres with distinct ecosystems may be as simple as housebuilding is for us today.

    • Ashley Baldwin January 19, 2017, 16:46

      I wouldn’t worry about alien bacteria. It’s all down to ecosystems again. Life doesent evolve in isolation but as part of a constantly interacting network which evolves too.” Exo Bacteria” will have evolved in a totally seperately over billions of years and are highly unlikely to interact with us having evolved in concert with the other utterly different organisms in their own ecosystem. Even assuming they are identifiable as bacteria analogues . No prior contact to develop as a threat .

      There is good evidence that many if not all of the most deadly pathogenic microorganisms arose as harmless strains in domesticated animals before subsequent transmission and mutation ” evolution” into deadly forms in human hosts . Cowpox is the classic example. Pasteur revolutionised medicine with his recognition that inoculation of it into people induced immunity to the closely related but deadly scourge , small pox. How coincidental. Or not… Quite likely smallpox originally arose from mutation of the self same cowpox generations earlier after transmission from some Stone Age cow herd living in near constant contact with his animals .The same with Measles which is closely related to a similarly benign sheep virus . Familiarity breeds contempt .

      • ole burde January 20, 2017, 10:07

        ”I wouldn’t worry about alien bacteria.” Allways good to be an optimist ! ..but sadly pessimists have a higher survival rate ! …single celled life has the ability to adapt by multible mutations to allmost anything very fast , and specialy to any new kind of food-supply …such as us ….some bacteria now happily eats antibiotics that would kill their ancestors a few years ago, even if these antibiotics are unlike anything existing in nature .. On the other hand the immune system of a highly developed mammal has limits to its ability to recognize patogens , and to procces this information into the production of effectiv antibodies . It is not at present possible to predict if our immune systems would be effective against exo-life , even if this should be made of a DNA analog ….and it probably wont be easy to get a goverment permission to experiment in this direction …

        • xcalibur January 21, 2017, 2:09

          I’d like to point out that extraterrestrial life may have different chirality than life on earth. If so, that would render the aliens incompatible with our life — they couldn’t eat or infect us, we couldn’t eat or infect them.

    • Ashley Baldwin January 19, 2017, 17:41

      Ravi Kopparupu built on Jim Kasting’s work to envisage an inwards extension of the erstwhile planetary habitable zone on Earth size planets but with a low starting load of water. ( he calls it “early Venus” , before runaway greenhouse had taken over ) . The heat of the nearby star starts off the process by photodissociation of escaping water as per Venus , H2 is lost to space allowing the build up of left over heavier O2. On ocean planets this could create crushing multi bar O2 atmospheres for at least a period before the heat allows energetic atomic oxygen to escape before O2 formation . However , on a much dryer initial planet the process might be curtailed leaving a hypothetically breathable 1 bar O2 atmosphere and arrest of the runaway greenhouse . No oceans obviously , but there would still be subsurface water that would rise in places to form artesian wells and oases. Quite literally “Dune” .But like Dune ( Herbert’s Arrakis) how sustainable would this environment be.Could life even arise there ?

      No oceanic water probably means no plate tectonics which means no Earth like vulcanism and not much CO2 , the raw material of photolysis driven photosynthesis and ultimately both the organic and inorganic carbon cycles so key to maintaining Earth’s regulating thermostat .

      ” Modern” Venus has this problem too but releases its internal heat instead through its bone dry ” stagnant lid” of a crust that melts cataclysmically en masse every few hundred million years or so ( likely adding to the 90 bar CO2 atmosphere in the process ) . Not exactly ideal for the formation and maintenance of life. Life that on Earth originated long before there was even O2 to utilise and only evolved to use it much later. Would there be enough CO2 to act as the electron donor for photosynthesis without excessive greenhouse effect and how would it be recycled ? With no carbon/silicate “weathering” inorganic process that would leave just the biological alternative via respiration / photosynthesis . Which requires photosynthesising life first , which in turn requires CO2 ( there are alternative electron donors like Hydrogen Suphide but that only tends to occur around deep ocean vents,”Black smokers” , which may exist on Europa but not on this planet as there would be no oceans . This reducing gas ,like methane, couldn’t exist for long in an all O2 atmosphere) .

      So , can a low water , O2 rich atmosphere planet remain stable long enough to evolve some kind of life ? The general consensus is that the two key requirements of life are water and energy . So maybe it is possible to conceive life arising on such a planet if stable for enough time . On Earth that was about half a billion years after formation . The clock is ticking .

      We might be able to wander around the surface without spacesuits but would need to bring supplies to live any time and any significant terraforming could easily disturb what would surely be a knife edge equilibrium. With such a different starting ecosystem any indigenous life would certainly need to be very different to survive .

      ……No giant worms need apply . Apart from sand, what would they eat ?

      Humans might be able to undergo short surface exploratory excursions but to live there permanently would be a different matter .

      • ole burde January 20, 2017, 9:45

        ”On ocean planets this could create crushing multi bar O2 atmospheres for at least a period before the heat allows energetic atomic oxygen to escape before O2 formation . ” …True enogh , it COULD create too much oxygen given enoug time , but on earth , which is close to being a waterworld , the process of oxygen saturation without life was extreemely slow . It would probably have taken billions of years more to reach saturation point where free oxygen starts to acumulate ….and it may be possible to calculate an estimate of just how long it would take …and it may also be possible to calculate for how long a period a planet of this kind would stay in the ”window of oportunity ” , where the oxygen is being produced more or less at the same rate it is being consumed . This may be a very long period ,because many oxygenation process’s wil only get started above a certain minimum oxygen pressure .
        I have read several estimates to how long Terraforming could take on a ”Young Earth” type planet , and they are not good …in the best case perhabs 50 milion of years , so it becomes logic to look for an older earthlike planet where photodissociation over several billions of years , has already done most of the SAME work that life could have done ten times faster times ….leaving the potential for a much faster terraforming process

  • Alex Tolley January 18, 2017, 19:54

    The Se data is non-quantitative, and their lower bound estimates for O2 are still consistent with the sort of O2 levels at the beginning of the GOE. It may be important to recognize that the abundance of non-sessile forms flowered when O2 levels were much higher.

    What this data indicates to me is that there was the potential for some aerobic organisms to live at an earlier period than we have so far found solid fossil evidence for. If so, they may have subsequently gone extinct as the molecular clocks don’t indicate any modern forms have evolved from them.

    It is still important to recognize that the evolution of photosynthesis was the key factor that allowed Earth’s atmosphere to become oxidizing, rather than reducing, and that aerobic respiration which liberates far more energy than anaerobic respiration, allowed the evolution of the animals we have seen from the Cambrian until today. It is the evolution of photosynthesis that needs to be common if we are to expect to find highly energetic life forms and probably technology on terrestrial worlds in the habitable zone.

  • Jim Early January 19, 2017, 9:56

    Baldwin’s comment about non-biological generation of oxygen is corrext. The photo dissociation of water is more importent for hot atmosheres such as Venus where water can rise higher in the atmosphere. Chris Makay pointed out about a decade ago that for the early Earth photo dissociation of methane played a similar role of allowing hydrogen to escape.

    These geological rates of oxygen generation are low, but they make it difficult to determine the very early rates of biological activity based simply on evidence of oxidation of the ocean’s iron.

  • Scott January 19, 2017, 17:33

    For ‘complex’ life to evolve on earth, you need Eukarya, which probably weren’t around during the oxygen pulses described in the paper. Recent work on Lokiarchaeota suggests that the requisite fusion events happened much more recently than previously thought.

    Here’s some background on it: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4594999/

  • Alex Tolley January 19, 2017, 17:45

    Animals that live in anoxic conditions and do not have mitochondria have been found in the Mediterranean Sea.

    The first metazoa living in permanently anoxic conditions.

    If this is a true finding, then it upends the idea that multicellular complex animals need oxygen, and that just possibly similar forms could have evolved before the GOE.

    It also means that just possibly such animals could evolve in other anoxic environments on exoplanets or possibly in the subsurface oceans of icy moons.

  • Geoffrey Hillend January 19, 2017, 19:01

    There was much more Co2 in the early atmosphere 3.85 billion years ago. We can assume that it increased after that time as the result of volcanism. There was more methane as well which which was expelled by volcanoes or made by chemical combinations of volcanic gases water vapor, hydrogen chloride, carbon monoxide, carbon dioxide, and nitrogen. http://www.indiana.edu/~geol105b/1425chap10.htm

    Methane is a more potent greenhouse gas than Co2 but there was still more Co2 than methane. Also life prefers a ratio of higher C12 than C13 which have been used by geochemists to postulate the age when life began. http://www.indiana.edu/~geol105b/1425chap10.htm

  • Geoffrey Hillend January 19, 2017, 19:03
  • Geoffrey Hillend January 19, 2017, 19:32

    Mark T. The thicker the atmosphere the stronger the greenhouse effect. Even if there were no greenhouse gases, a thicker atmosphere will still have a greater greenhouse effect. Source: The Scientific Exploration of Venus. I don’t think Earths atmosphere was ten time thicker then as the result of a lower temperature than Venus. H20 formed the hydrosphere or sea and became liquid. Rain takes the Co2 out of the atmosphere as the result of the Urey reaction and carbon cycle. It is clear that Co2 was removed from our atmosphere over time by life or micro-organisms and planet life and as a consequence the carbon cycle is becoming out of balance and Ph of the oceans is going down due to increased Co2 levels and acidity going up.

    • Ashley Baldwin January 21, 2017, 20:29

      Life on Earth predates the GOE by at least a billion years and photosynthesising life by definition must also by a long period to build up atmospheric O2 . It’s likely that the chloroplasts that allowed Cyanobacteria to adopt this ingenious direct use of the Sun’s energy were originally independent organisms that entered into symbiosis ( getting nutrients , protein etc in return) with primitive bacteria . So life was rapidly developing in complexity well prior to large amounts of free O2 initially created as a toxic byproduct . Is this happening anywhere else and could we recognise it from afar ?

      There was a review on “hazes” in the early “Archean” atmosphere of Earth published by Arney et al in October. They are essentially smog created by photolysis of atmospheric CH4 and CO2 and their subsequent polymerisation into longer chain hydrocarbons like C2H2 ,acetylene and C2H6, ethane . To some extent the CO2 acts as a buffer to this with the ratio of CH4/CO2 vital with peak haze at 0.2 . At this point photolysis of the two gases that created the haze is cut off by the UV blocking effect of the haze itself to form a negative feedback loop.

      Modern Titan has hydrocarbon hazes too but with no CO2 form more easily and without as aggressive feedback. A key difference with Archean Earth type conditions along with the far lower temperature involved and other nitrogen containing nitrile molecules .

      Hazes block out sunlight lowering planetary temperature and countering the greenhouse effect of CH4, CO2 and C2H6 . They helped habitability by selectively absorbing shorter, bluer wavelengths and dangerous UV ( up to 97 %) at a time when no O2 meant no protective O3, and by allowing through longer wave visible and near infrared light which was then absorbed by surface ice reducing its albedo and melting it . Even sub freezing point temperatures would not invariably lead to extensive glaciation despite a 20% dimmer Sun 2.7 billion yra. ( or of course planets orbiting dimmer M dwarf stars which radiate in these wavelengths – see below ) Archean hazes are associated with CH4 ,CO2, C2H6 and CO absorption spectra with their own “fingerprint” absorption occurring at 6 microns . All would show up on a remote transit spectrum .

      Hazes occur at all heights in the atmosphere , and are also associated with H2O absorption spectra which along with all of the above are also detectable by remote transit spectroscopy. Crucially though, thanks to atmospheric refraction the atmosphere of Earth like planets around Sunlike stars this technique can only operate down to 20kms , well above the lower atmosphere troposphere. Nearly all of Earth’s H2O sits in the troposphere , , just as well- any planet with stratospheric H2O is likely to be a hot analogue of early Venus in the process of runaway greenhouse .

      ( This refraction is generally a nuisance of course , but is far less around M dwarf stars where the technique can reach into the upper troposphere offering the opportunity to find O2 and H2O where with O4 they might indeed be biomarkers in an oxidative atmosphere )

      What does all of this mean ? Well put it all together and with an Exo planet sitting in the habitable zone of a Sunlike star ( Late F- Early K class ) , with terrestrial mass, and displaying the detectable spectrum just described probably represents a biomarker despite NOT having any O2. An Archean exoEarth or “Pale Orange Dot” as aptly named by Arney et al. Given that inhabited Earth existed in this state for well over a billion years there could be many such planets .

      Even at this early point biotic production of CH4 probably significantly out weighed abiotic production via hydration of rock like olivine and pyroxenes , so called ” serpentisation” , so it’s potent greenhouse effect probably played a role in heating early Earth when haze free .( and illustrating just how potent the biological process of methanogenesis is , with extrapolations suggesting even a 5 Me inhabited ” ExoArchean” planet would exhibit this trend )

      The review also looked at recent evidence suggesting that surface atmospheric pressure at this time was only about 0.5 bar .

    • Mark T. January 24, 2017, 13:32

      Geoffrey, I have no basis for thinking the Earth’s atmosphere was ten times thicker more recently either, but it very well may have been ten times thinker, or even more, prior to the probable impact of Theia. Even so, what I am driving at is I suspect planets with such thick atmospheres may have an even more difficult time reaching the same percentage of oxygen, assuming percentage is the key metric. I readily admit I do not know the answer, and in fact, let me suggest nobody does (nobody human anyway). There are so many variables to consider with so many unknowns, it is extremely hard to come to any firm conclusions. A larger atmosphere should mean greater UV protection and warming, but also greater hazes cutting down on the potential for photosynthesis. How life might evolve differently in such circumstances is a giant wildcard. Life often does the exact opposite of what one might expect from first order effects, so in this case, it might run riot under that hazy atmosphere and oxygenate the whole planet much faster than Earth’s atmosphere did, although I suspect that is not true.

      My point is that habitable zone planets with large atmospheres may struggle to oxygenate them enough to support evolution of alien civilizations, and this could be the biggest reason why alien civilizations seem absent. Without a breathable O2 atmosphere, any life would be restricted to more simple creatures, probably.

  • Geoffrey Hillend January 19, 2017, 19:39

    As a consequence of the 30 billion tons of Co2 produced by coal power plants and other man-made greenhouse gases, the carbon cycle is becoming out of balance.

  • Geoffrey Hillend January 19, 2017, 19:40

    roughly 30 billion tons per year.

  • xcalibur January 21, 2017, 2:13

    I’d like to venture a hypothesis: maybe oxygen kept increasing until aerobic life evolved to take advantage of it, which in turn caused oxygen levels to stabilize.

    • Alex Tolley January 21, 2017, 18:00

      That hypothesis is already falsified. Complex life started at very low levels of O2 partial pressure. O2 pressures peaked during the Carboniferous (supporting all those massive arthropods) due to the extent of photosynthesis and before fungi evolved to break down lignin in trees (which is why we have such extensive coal beds from that era).

      Fire seems to the factor limiting O2 pressures, not life processes, on a living planet. On an abiotic, water world presumably, photolysis will allow O2 levels to exceed Earth’s.

  • Geoffrey Hillend January 21, 2017, 18:44

    It is a hypothesis that is mainstream by scientists today since ultra-violet radiation still reached the surface of land and water but not too far below water at the time of the first appearance of life, bacteria and blue green algae beneath the sea.

    Ultra violet radiation from the Sun actually splits molecular oxygen O2 into O1 which combine to form triatomic oxygen or ozone O3. Ozone absorbs electromagnetic radiation between 200 and 300 nanometers or .2 and .3 microns which is in the ultra violet spectrum. The ground state of the electron of every atom is equal to a certain wavelength. It can only absorb electromagnetic radiation at very distinct or specific frequency which is a resonant wavelength or the same frequency as its ground state. All other electromagnetic radiation gamma rays, x rays, visible light, infra red and radio waves pass right through the ozone molecule but it is opaque to ultra violet. It scatters ultra violet light which is why it is a shield for us from it. A small amount of it does get through and causes sun burn but if there were no ozone, life would perish.

  • Geoffrey Hillend January 21, 2017, 19:14

    Alex Tolley If you are referring to the Cambrian explosion, it had to be supported by planet life which of course had to be supported by ozone development so xcalibur’s hypothesis is correct. Life started as micro organisms which then made oxygen. Ozone came after with Aerobic life.

  • Geoffrey Hillend January 21, 2017, 19:15

    Excuse me, I meant Plant life

  • Michael Fidler January 30, 2017, 20:47

    Moon’s Been Getting Oxygen from Earth’s Plants for Billions of Years

    “The moon may carry material produced by life from Earth dating back to when plants first filled the planet’s air with oxygen, according to study of data from a Japanese lunar orbiter. ”

    “A team led by Kentaro Terada of Osaka University looked at data from the Selenological and Engineering Explorer, better known as Kaguya. The researchers found that a certain kind of oxygen isotope was present in the lunar soil, an isotope that occurs on Earth. ”

    http://www.space.com/35502-moon-has-oxygen-from-earth-plants.html

  • Michael Fidler February 13, 2017, 3:12

    Oxygen flooded Earth’s atmosphere earlier than thought.
    Volcanism and global glaciation coincided to the gas’s rise.
    We present U-Pb ages for the extensive Ongeluk large igneous province, a large-scale magmatic event that took place near the equator in the Paleoproterozoic Transvaal basin of southern Africa at ca. 2,426 Ma. This magmatism also dates the oldest Paleoproterozoic global glaciation and the onset of significant atmospheric oxygenation. This result forces a significant reinterpretation of the iconic Transvaal basin stratigraphy and implies that the oxygenation involved several oscillations in oxygen levels across 10−5 present atmospheric levels before the irreversible oxygenation of the atmosphere. Data also indicate that the Paleoproterozoic glaciations and oxygenation were ushered in by assembly of a large continental mass, extensive magmatism, and continental migration to near-equatorial latitudes, mirroring a similar chain of events in the Neoproterozoic.
    https://www.sciencenews.org/article/oxygen-flooded-earth%E2%80%99s-atmosphere-earlier-thought

    http://www.pnas.org/content/early/2017/01/31/1608824114.full.pdf?with-ds=yes

  • ljk March 1, 2017, 22:11

    Oldest microfossils suggest life thrived on Earth about 4 billion years ago

    Ancient microbes were spewed from deep-sea hydrothermal vents, study claims.

    BY MEGHAN ROSEN 1:00 PM, MARCH 1, 2017

    https://www.sciencenews.org/article/oldest-microfossils-suggest-life-thrived-earth-about-4-billion-years-ago?tgt=nr

    Earth’s Outer Shell: Was It Once Solid?

    By Kacey Deamer, Staff Writer | February 27, 2017 05:32 pm ET

    http://www.livescience.com/58034-earth-once-had-solid-outer-shell.html

  • ljk March 1, 2017, 23:14

    WHAT THE OLDEST FOSSIL ON EARTH MEANS FOR FINDING LIFE ON MARS

    Article Updated: 1 March 2017

    by Nancy Atkinson

    Scientists have found evidence that life existed on Earth much earlier than previously thought and they say this discovery has implications for life springing up on other planets, particularly Mars.

    Fossils of microscopic bacteria were discovered in Quebec, Canada in the Nuvvuagittuq Supracrustal Belt, a formation which contains some of the oldest sedimentary rocks in the world. Scientists estimate the fossils are at least 3.7 billion years old, and could be as old as 4.28 billion years. This is hundreds of millions of years older than previously found specimens.

    “The most exciting thing about this discovery is that we know life managed to get a grip and start on Earth at such an early time in Earth’s evolution, which gives us exciting questions as to whether we are alone in the solar system or in the universe,” said PhD student Matthew Dodd from University College London (UCL), who is the first author on a new paper about the finding in the journal Nature. “If life happened so quickly on Earth then could we expect it to be a simple process and start on other planets, or was Earth really just a special case?”

    Full article here:

    http://www.universetoday.com/134030/oldest-fossil-earth-means-finding-life-mars/

  • ljk March 15, 2017, 12:45

    A perfect storm of fire and ice may have led to snowball Earth

    Explaining a “once-in-a-billion-year event”

    By Leah Burrows

    What caused the largest glaciation event in Earth’s history, known as ‘snowball Earth’?

    Geologists and climate scientists have been searching for the answer for years but the root cause of the phenomenon remains elusive.

    Now, Harvard University researchers have a new hypothesis about what caused the runaway glaciation that covered the Earth pole-to-pole in ice.
    The research is published in Geophysical Research Letters.

    Researchers have pinpointed the start of what’s known as the Sturtian snowball Earth event to about 717 million years ago — give or take a few 100,000 years. At around that time, a huge volcanic event devastated an area from present day Alaska to Greenland.

    Coincidence?

    Harvard professors Francis Macdonald and Robin Wordsworth thought not.
    “We know that volcanic activity can have a major effect on the environment, so the big question was, how are these two events related,” said Macdonald, the John L. Loeb Associate Professor of the Natural Sciences.

    March 13, 2017

    Full article here:

    http://www.seas.harvard.edu/news/2017/03/perfect-storm-of-fire-and-ice-may-have-led-to-snowball-earth

    To quote:

    “It’s easy to think of climate as this immense system that is very difficult to change and in many ways that’s true. But there have been very dramatic changes in the past and there’s every possibility that as sudden of a change could happen in the future as well,” said Wordsworth.

    Understanding how these dramatic changes occur could help researchers better understand how extinctions occurred, how proposed geoengineering approaches may impact climate and how climates change on other planets.

    “This research shows that we need to get away from a simple paradigm of exoplanets, just thinking about stable equilibrium conditions and habitable zones,” said Wordsworth. “We know that Earth is a dynamic and active place that has had sharp transitions. There is every reason to believe that rapid climate transitions of this type are the norm on planets, rather than the exception.”

  • ljk May 10, 2017, 13:17

    Oldest Evidence of Life on Earth Possibly Found in Australian Rocks

    By Tia Ghose, Senior Writer | May 9, 2017 11:00 am ET

    Ancient rocks found in a remote stretch of Western Australia may contain the world’s oldest known evidence of life on land, a new study finds.

    The 3.48-billion-year-old rocks are part of an area known as the Dresser Formation, located in Pilbara, Australia. During Earth’s early years, the region might have been a volcanic caldera (a volcanic crater often resulting from an eruption) on a small island dotted with hot springs and ponds that were teeming with microbial life, said study lead author Tara Djokic, a doctoral candidate in geosciences at the University of New South Wales in Australia.

    Djokic and her colleagues found signs of microbial life embedded in rocks that form around hot springs, as well as in deposits in the ancient hot springs themselves.

    The findings hint that early life may have gotten its start in hot springs on land, as opposed to deep inside ocean hydrothermal vents, as is commonly believed, Djokic told Live Science.

    [Why not both? Why does it or why would it have to be one or the other? And are these the only two “answers”?]

    Full article here:

    http://www.livescience.com/59025-oldest-evidence-for-life-found-in-australia.html

    To quote:

    The new study is fascinating and convincing, said Robert Hazen, a mineralogist and astrobiologist at the Carnegie Institution for Science who was not involved in the research.

    “Maybe it would be more surprising if there wasn’t some ability for life to seize this kind of environment,” Hazen told Live Science. “You have chemical energy, which you need; you have mineral surfaces, which can provide a protective environment. It seems like a pretty nice place to make a living if you’re a microbe.”

    The new samples may provide the oldest solid evidence of ancient life, he added.

    Though even older rocks in Quebec and others in Greenland may contain traces of potential life, those rocks have been tilted, stretched, baked and changed in many ways since their formation, Hazen said. As a result, it’s hard to make conclusions about what really happened so long ago, and determine whether the traces of life are indeed evidence of life and, if so, if they truly come from the primeval period when the rock first formed, Hazen said.

    By contrast, the Pilbara region contains pillowy rocks that look essentially the same as they did 3.48 billion years ago, making it much easier to make claims about the ancient environment, Hazen said.

  • ljk June 19, 2017, 9:52

    This guy says Earth life is not in the middle of a sixth mass extinction event:

    http://www.dailygalaxy.com/my_weblog/2017/06/we-are-not-in-the-middle-of-a-sixth-mass-extinction-earths-past-armageddons-unfolded-like-human-powe.html

    I can only hope this isn’t yet another variation on the whole global warming issue, where science is being driven by politics, popular vote, and just plain raw emotions. Forgive me for being paranoid here, but I think my reaction is justified these days.

    • Alex Tolley June 19, 2017, 11:49

      I don’t think his argument is totally wrong. He isn’t saying we are not in the midst of one, just that so far we haven’t done the damage that we see in the 5 great extinction events when you compare the losses. He is right that the fossil record is very thin compared to what was probably around, but that shouldn’t mean that we should therefore ignore the loss of species we can see around us. That loss is real, and the projected losses are high if all endangered species were to be wiped out. Species that we think are abundant might suddenly disappear with ecosystem collapse. Recently I read that which species lose can be predicted by which species are late to acquire nesting sites in a warming world where sites are being diminished. It’s all rather non-linear and we should not be complacent.

  • ljk July 13, 2017, 15:20

    Researchers turn to da Vinci for new perspective in search for alien life

    Researchers are using an idea by Leonardo da Vinci to search for extraterrestrial life by examining traces it would have left behind, such as borings, burrows and tracks, according to a study published in Earth-Science Reviews.

    “Leonardo understood the biological nature of borings based on their shape, not their biochemistry,” said lead study author Andrea Baucon.

    Full article here:

    https://www.seeker.com/space/finding-extraterrestrial-life-may-rely-on-identifying-traces-rather-than-aliens