Some evidence that life may have originated at least 4.1 billion years ago

April 29, 2016 • 10:30 am

For some reason I missed this paper published last November in Proc. Nat. Acad. Sci. USA by Elizabeth Bell et al. , and it doesn’t seem to have been given a lot of attention by the press. That may be because its conclusions are questionable, and based on a very small sample. But if they’re right, it’s a pretty amazing result, for the authors report the presence of what may be biogenic carbon—that is, carbon derived from living organisms—from the Jack Hills of western Australia, and that carbon was dated at 4.1 billion years old.  Since the Earth is about 4.54 billion years old, and the zircons of the Jack Hills are the oldest known material of terrestrial origin on our planet (4.4 billion years is the oldest sample), the finding of biogenic life in zircons dated at 4.1 billion years means that life may have originated very, very soon after the Earth formed. But these findings are preliminary.

The oldest widely accepted evidence of life on Earth are 3.4 billion year old microfossils from the cratons of the Strelley Pool formation, also from Western Australia. (Old, stable parts of the Earth are called “cratons.”) To get older evidence than that, you have to date and do isotopic analysis of flecks of graphite that may be derived from organisms. The oldest carbon generally accepted as being of biological origin is about 3.8 billion years old.

The dating is done by radiometrically dating the minerals containing graphite (carbon) flecks (usually zircon derived from melting earlier “mud rocks” that presumably contained organismal remains), and the biogenic origin is studied by looking at the amounts of carbon 13 versus carbon 12 in the flecks. Non-organismal carbon has a relatively higher amount of carbon 13 than does biogenic carbon.(The different ratios come from the fact that organisms absorb atmospheric carbon into their bodies, which is higher in carbon-12 than inorganic carbon). The values of these isotopes are transformed into a statistic called δ13Cδ13C values  of 24 or lower are generally assumed to be signatures of carbon derived from organisms.

At any rate, Bell et al. dated zircons found in the Jack Hills. One of them contained carbon flecks (and was crack-free, so the graphite didn’t insinuate itself after the zircon was formed); and for that sample they determined the average δ13C of the flecks using spectral analysis.

Here’s the prepared zircon with the flecks inside. The bar is 30 microns long, or about a thousandth of an inch.

Fig. 1. (from paper) Transmission X-ray image of RSES 61-18.8 with graphite indicated. (Inset) Raman spectra for the top inclusion and for an epoxy “inclusion” from another investigated zircon. The broadened “D-band” at ∼1,400 cm−1 indicates disordered graphite (39); C–H stretch bands at ∼2,800–3,100 cm−1 (39) are observed in epoxy but not graphite.

And here’s the average value of  δ13C  (triangle) for the Jack Hills sample, compared with the ratios for 3.8-billion-year old graphite that is widely accepted as being organic in origin.  The average value of the Jack Hills carbon was -24, so it’s within the range of organic carbon; i.e. life might have been around by 4.1 billon years ago. That would extend the origin of life back another 300 million years beyond what we know, so that life may have originated no more than 500 million years after the Earth formed.

Screen Shot 2016-04-29 at 9.54.26 AM
Fig. 2 (from paper) δ13C for Eoarchean–Hadean carbon samples measured via SIMS vs. host mineral age compared with inorganic and organic carbon (organic carbon values from ref. 13; inorganic from ref. 14).

Now the authors note that there are other processes that could produce low values of δ13C, including the Fischer-Tropsch chemical process, carbon derived from meteorites, isotope fractionation by diffusion, and so on, but they claim that a biogenic origin is “at least as plausible” as these (not a strong statement!).

I won’t go write further, as I only wanted to call your attention to some tantalizing evidence that life may have been around a lot earlier than we thought. Whether this becomes widely accepted will take a while—and much more work. After all, this paper is based on just a single sliver of zircon. If you want to see the entire paper, and can’t get it from the link below, just ask.

h/t: Latha Menon


Bell, E. A., P. Boehnke, T. M. Harrison, and W. L. Mao. 2015. Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon. Proceedings of the National Academy of Sciences 112:14518-14521.

101 thoughts on “Some evidence that life may have originated at least 4.1 billion years ago

    1. I usually read the posts on the homepage, sometimes when scrolling down I come to the comments of a specific post, or I continue scrolling once I’ve read a post to the next one below.
      Does that at all show up on the stats Jerry has talked about when looking at what his readers read of his content?
      (Also liked the post, thought of this and that’s why I came to the comments, don’t have anything substantive to add as I’m not familiar with the subject matter but still read it with pleasure.)

      1. If you only read the posts via the home page, the fact you’ve read a post won’t be included in its stats. You need to go to its individual page for that.

        1. Interesting. That may skew his results somewhat, since I, for one, often read the entirety of a science post on the home page, and often don’t go to the individual page. Maybe others do the same. Perhaps if the original post were truncated and one had to click on it to see the rest the stats would improve.

          1. That’s why they’re truncated on my own home page. Gotta get those clicks to drive ratings on Google! 🙂 Jerry’s popular enough not to need to do stuff like that, but I’m sure his science posts are read more than he thinks. They don’t get many comments, but you have to actually click onto the page to comment, so I think you’re right.

  1. In this case I’m more impressed that we can figure out how to figure out how old it is than I am with the results.
    Gotta love science.

    1. I have a longish comment with a longish section on that under moderation for too many link references.

      The short version is that Abramov et al has shown that even mesophilic prokaryotes would survive known LHB rates, because they spread and procreate faster than the bombardment sterilizes crust.

      Moreover for what it is worth, there is something of a tension between astrophysics modeling data and geological mineral data, in that no zircons older than 3.5 Ga show the impact shock fractures seen in zircons around young craters.

        1. Jerry, you are filled with energy! [And I am filled with soporific pain killers. :-/]

          I don’t know how you get so much done.

    1. “This finding seems to support the idea that the spontaneous origin of life is a more likely event than creationists maintain.”

      Yeah I heard about this significantly earlier than last November. I don’t know if it was early information released about this paper, or speculation based on evidence available at the time, but I found it memorable due to that reason.

      1. Ysm, you are missing that it can be seen as us observing a process. That process is fast, indicating that it is mechanistically easy and/or repeated very often under habitable conditions.

  2. Imagine life beginning so very far back, at the very edge of planet formation. Is life, at least rudimentary life, part of planet formation in general? Will the universe be rich with life wherever we look? It was Dawkins, I believe, who said wherever we find life, it will be evolving!

    1. I’d agree that life [by definition, evolving] should be near-universal on planets as benign as earth. But, it would seem, likely to be pretty much all unicellular, and largely prokaryotic grade.

      That’s exciting! But we really shouldn’t expect anything from SETI and similar initiatives.

      1. We should expect a negative, setting an upper bound on frequency of “us”. Something quantitative, at least.

      2. These findings lead us nearly inevitably to The Fermi Paradox (“Where is everybody?”).

        The problem for the origin of life here is that we have a sample of 1 (unless we find that prokaryotic life originated more than once and was taken over by one particular line). Is the appearance of life in general more probable if it appeared after 500 million years after the Earth’s formation than if it appeared after 800 million years? It somehow feels that way, but is that probability quantifiable?

        And if life originates easily -as we suspect- and nobody is there, is there a Great Filter? or is it something as mundane as too long distances (too expensive to travel).
        And if there is a Great Filter, we should hope it is behind us (e.g. eukaryotic -mitochondrial- life) and not ahead of us (e.g. technologically sophisticated societies always allow some lonesome loony to create Armageddon)…. (sorry for the many alliterations in the last sentence: unintended)

        1. Interstellar communication would be extraordinarily expensive for a civilization anything like what we can reasonably anticipate for humanity for centuries at least. And interstellar travel of any consequence requires energy and technology so far beyond humanity that the Romans were in a better position to speculate about colonizing Mars.



          1. Yes, very true. That is why I mentioned that possibility negating the necessity of the Great Filter.
            But look at it: in the last 2000 years we made more technological/scientific progress than in the last 20 000 years (and there more that in the last 200.000 years)
            In the last 200 years more progress than in the last 2000 years, and arguably more progress in the last 2 decades than in the last 200 years (definitely if we look at Moore’s law of processing power). So our knowledge and technical abilities accelerate if not exponentially -which I suspect- at least squarely or parabolically.
            How would we do in another 2000 or 200 000 years?
            So it appears to me there probably *is* a Great Filter (or many smaller filters? anther straw).
            And I fear -my greatest fear- that it is not behind us….
            That is why reading Nick Lane’s “Power, Sex and Death: mitochondria and the meaning of life” was a kind of straw to give some hope it might be behind us after all.

            1. Be very wary of extrapolation.


              Interstellar travel only makes economic sense when you’re using such a significant portion of your star’s output that you need to start colonizing other systems to use their stars for energy. But if that’s the case, your exponential growth isn’t going to stop with a mere few systems, but continue until you’ve overrun at least the galaxy.

              It only takes about 25 doublings to exhaust all the stars in the galaxy. Pick whatever timeframe you want for a civilization to colonize another star, multiply by 25, and that’s when said civilization runs out of stars. Even at something ludicrous like 10,000,000 years between colonizations would mean that a civilization that started at Earth’s age of dinosaurs would be out of stars in the galaxy by now. And the dinosaurs only arrived on the scene in the last 5% of the age of the Earth, or the last 2% of the age of the Universe.

              To put things in further perspective…our entire civilization only uses the equivalent of about the total Solar influx that reaches a small state on the Eastern Seaboard. We don’t even use a noticeable fraction of the Solar output that reaches the Earth — and the Earth itself receives a far smaller fraction of the total Solar output. For us to ponder engineering on that scale is as silly as a duck wondering what to do with the entire ocean.




          2. Frank Drake, speaking at a SETI conference in 1972:

            To illustrate how effective electromagnetic waves may be, we can take as an example in the radiofrequency range the existing Arecibo radar. […] the range works out to be 2000 parsecs, or about 6000 light years, which is a very large range. In a few years this will become some 20,000 parsecs, meaning that the Arecibo radar will be visible to similar instruments throughout the galaxy.

            This seems at odds with your claim that “Interstellar communication would be extraordinarily expensive for a civilization anything like what we can reasonably anticipate”.

            1. First, 6000 light years is just a few percent of the diameter of the Milky Way — about comparable to sending a radio signal a few hundred miles on Earth.

              Second…I have a very hard time believing that, even at those distances, it’ll even be theoretically possible to pick out an Aricebo signal against the noise of the Sun. Just because you can pick out a candle on the far side of the valley in the middle of the night doesn’t mean you’ll be able to see it during the day….



              1. 6000 light years may not be a large fraction of the galaxy, but there are still many millions of stars within that distance.

                And for much of the last century, Earth has outshone the sun at microwave frequencies. Military radar and TV broadcasts are the two principle sources of emission (although TV leakage has decreased somewhat with the growth of cable and satellite TV). Here is a NASA paper, which I found in about 30 seconds of googling, that explains why your personal incredulity about the detectability of such emissions is wrong.

              2. From SETI’s FAQ:

                If an extraterrestrial civilization has a SETI project similar to our own, could they detect signals from Earth?

                In general, no. Most earthly transmissions are too weak to be found by equipment similar to ours at the distance of even the nearest star. But there are some important exceptions. High-powered radars and the Arecibo broadcast of 1974 (which lasted for only three minutes) could be detected at distances of tens to hundreds of light-years with a setup similar to our best SETI experiments.

        2. There could be an Earth-like civilization just 4 light years away at Alpha Centauri, and all the SETI radio telescopes in the world still couldn’t detect it. SETI’s only chance of detecting alien intelligence is for someone on a nearby planet to beam an incredibly high-powered radio laser directly at us, and have it arrive right when SETI happens to be looking in its direction.

          So I wouldn’t get too worried about Great Filters just yet. The Universe could be teeming with life that we just can’t see.

        3. I don’t see any of those as problems:

          – The Hart-Tipler argument on Fermi’s Question is not a valid hypothesis as I understand it, since it has untestable corner cases. (We can’t estimate frequency of false negatives.)

          Fermi’s own Answer is still valid and the best: We don’t know that interstellar travel is possible. [ ]

          – As I noted, emergence of life is a process, not an isolated sample. (And you yourself notes how rapid emergence translates into an easy process.)

          – The GF depends on the HT argument.

          But even if it had a valid basis, it isn’t a valid hypothesis. Same as for the Rare Earth model you can pick factors so that you can choose any likelihood between 0 and 1 you wish.

  3. It hadn’t occurred to me that F-T could occur naturally.

    It’s worth noting that F-T provides a not-unreasonable limit on the price of petrochemical-type products. It’s energy-intensive and not cheap compared with historical mining efforts. To be economical, you need a so-called “alternative” energy source that doesn’t involve digging hydrocarbons out of the ground. But you can, for example, produce diesel- and gasoline-equivalent fuels from atmospheric CO2 using solar photovoltaics as your energy source. If I remember right, it’s cost-competitive with fossil fuels in the $150 / barrel range, certainly by the $200 / barrel range. With solar prices in freefall, it could well be closer to $100 / barrel by now or soon.

    That’s good and bad. It means that we can keep driving gasoline-powered cars and running diesel-powered farm and transportation equipment and flying kerosene-powered jet air craft indefinitely. But nobody’s sure if our economy can actually function with energy prices that high…plus there’s all the stranded assets that leaves the oil companies with (if anybody is “too big to fail,” it’s them). Oh — and we’d have to build up all this alternative infrastructure in the midst of all this economic chaos, at a time when oil wells are starting to run dry, leaving us with less and less energy to bootstrap all this industry in the first place.

    “Interesting times,” indeed….


    1. That seems like an interesting idea that I haven’t head of. It sounds incredibly inefficient though with so many energy transformations. Solar energy to electrical to chemical to thermal to kinetic – with losses at each step. I suppose it has the advantage of utilizing all the existing infrastructure. This just goes to show how critical energy storage is to the successful conversion to renewables since the whole solar+F-T thing is just an elaborate storage and transport mechanism for sunshine. Then again, so am I.

      1. There’re multiple layers of problems with battery storage. We’ve only just now developed them to the point that you can build a good car with one — and, even still, there’s a price premium associated with them that doesn’t make economic sense with today’s gasoline prices. Don’t get me worng; I’m still planning on going electric, and the benefits from electric go far beyond economics. But they still lag, and significantly, on the economics.

        …but that’s just passenger vehicles. We’re nowhere near the point where we could run our cargo transportation system on batteries, let alone agribusiness, let alone air transport. Even NASA couldn’t build a battery-powered airliner today no matter what kind of budget you threw at them…about the best anybody is actually doing is small training aircraft with well under an hour of endurance.

        And then there’s the whole question of feedstocks for plastics, fertilizers, lubricants, pesticides, and all that. Pretty much all of that starts with liquid hydrocarbons.

        So, if you want to have crops and harvest them and if you want the industrial base to get those crops to your table, we need liquid hydrocarbons, and we’re going to need them for many decades. We could electrify the entire passenger fleet tomorrow, and the only real significance that would have is to free up part of the supply for industry. We’re all intimately aware of the role gasoline plays in cars, but that’s just a small and relatively insignificant piece of the puzzle.

        So…the way forward, if there actually is a way forward, involves synthetic liquid hydrocarbons made with solar energy. The big question is whether or not it’s even theoretically possible to do that with the modern economy as it’s structured — plus the minor details of all the powerful vested interests who stand to lose their shirts in the short term as we perform any sort of transformation. If there’s a saving grace, it’s that it’s already becoming common knowledge that those powers have built their strength on assets that are increasingly becoming obviously stranded, meaning even the perception of their power is weakening.



        1. Producing liquid fuels from the PV produced energy takes care of the distribution problem and thus allows you to optimally site the installation. This is good and is a major advantage over batteries or simply pumping the energy into the grid but doesn’t overcome the scale of the problem. PV panels are improving rapidly but they are still very inefficient. To power our society with PV you would need an incredible amount of land dedicated to solar installations. Some googling and back of the envelope calculations (CAUTION! many assumptions!) give me about 68 acres of PV (installed in Arizona) per American to produce their annual energy consumption (per capita US energy consumption is ~79,000 kW*h). Multiplied by 320 million you end up with a solar array roughly the size of South Carolina to supply all of the energy needs of the US. Is that realistic? Maybe, given the scale of the climate problem we face.

          I am an advocate for renewable energy but I don’t think we can seriously move away from hydrocarbons as rapidly as is needed without major disruptions. Nuclear energy seems to be the best choice but is far from perfect. I wish I had the answer.

          Interesting that this conversation started with a discussion of the age of life on earth. Another reason to love this site!

          1. Your envelope needs some recalibration. The PV panels you can buy of the shelf at your local home improvement store are plenty efficient. The typical American household needs less than 500 square feet of surface area for 100% net generation — and the typical American household is (substantially) more than 1,000 square feet. Domestic electric consumption is roughly half of total per-capita energy consumption, with the majority of the remainder coming from transportation (including personal vehicles). So, to a first approximation, all we have to do is cover residential rooftops and we’re golden — and that’s long before we get to commercial rooftops, parking lots, and other sorts of already-developed land.

            For details, see here:


            The money quote:

            This brings us to some practical matters. Returning to the PV efficiency snob, efficiency effectively maps to area. A typical location within the U.S. gets an annual average of 5 full-sun-equivalent hours per day. This means that the 1000 W/m² solar flux reaching the ground when the sun is straight overhead is effectively available for 5 hours each day. Each square meter of panel is therefore exposed to 5 kWh of solar energy per day. At 15% efficiency, our square meter captures and delivers 0.75 kWh of energy to the house. A typical American home uses 30 kWh of electricity per day, so we’d need 40 square meters of panels. This works out to 430 square feet, or about one sixth the typical American house’s roof (the roof area of a two-car garage). What’s the problem?

            (See the rest of the article for justification of those figures.)




            1. You haven’t given me any reason to revise my numbers. I’m not just talking about just residential electricity consumption (as heather said, that’s easy)- I’m talking about ALL energy consumed. It’s one thing to run your laptop on PV – it’s a whole other thing to run a steel mill or the factory that made the laptop. So instead of the 30kWh/d per household, it goes to something like 600 kwh/d per household.

              You have to include all the power required by the society outside your house that makes your life possible.

              1. The wikipedia table shows 83,617 kWh per capita per year for the USA so it was my numbers that were low, not yours.

              2. (9538.8 watts continuous) X (365 days/year) X (24 hours/day) / (1000 W/kW) = 83,560 kW*h/yr

            2. PV panels are really not the limiting factor here; as neither their cost, efficiency, lifespan, etc. is as much of an issue as energy storage. PV panel energy production during the day is not a good match for energy use during the day/night and so storage/conversion is a critical component. I would say this is the main impediment to greater use and not the surface area needed or cost of the PV panels. I only have grid tie at the moment and will not be increasing my small 2kw array (only personal use now as I would only get 1.5 cents per kwh from the utility) any further until battery technology improves (read: cheaper). When/if LiFePo4 or similar tech gets to <$250/kwh then we have a completely new game.

          2. There is more than just PV panels (apart from the fact that the surface of roofs in this world would cover a substantial part of South Carolina, as well as North for that matter). There is concentrated solar power (CSP), for example from heliostats with a power-tower, which uses much less space.

            The idea appears simple, but I marvel at the engineers who find this exciting and interesting -difficult in other words (eg. managing the hot salt solutions), while they find the photovoltaics simple and boring.

            Note, if we had (well, affordable) Tesla’s here in SA, I’d install PV panels on my roof, the car’s batteries doubling as house batteries.

            1. Solar thermal is neat, but it misses the point that really matters: we already have all we need. Rooftop solar is already at your local home improvement store next to the attic insulation. We’d be fools to not go with the excellent we already have in hopes of some imperfect better that only exists in design sketches.



              1. Agreed, the PV panels are OK. What is not (yet) OK is storage ie. batteries: expensive and limited lifetime.
                And here in SA these two-way electricity meters appear to be a nono. Eskom (our national electricity provider) says “Njet”.
                Hence I only have a black field solar geyser (boiler) at present.

              2. The saving grace there is that the existing grid works splendidly as a functional battery, and it will continue to do so for a loooong time. We won’t have any actual inherent problems with the grid until solar is generating so much during the daytime that the grid is in overproduction even with baseload generators at minimum. Before then it’s just grid operators doing the same demand adjustments they’ve always done, but with them generating less and less power as time goes on. And all the complaints about unpredictability are red herrings…solar averages out over geographical scales such that even fast-moving storm systems don’t pose a problem.

                We’re already at the economic point with batteries today where we were with panels themselves a couple decades ago…your return on investment works out to the equivalent of a few percent a year, not great, but not all that bad for something reasonably secure. By the time solar is putting out enough to pose challenges for the grid, batteries — in the home if nowhere else — will render that problem moot, too.



              3. I get the impression (e.g. from strongforce’s post above) that utilities charge a lot more per kWh that you take from the grid than they’re pay you for kWh that you contribute to the grid. So you can use the grid as a ‘battery’ but you’re gonna have to pay for it.

        2. That’s the thing that concerns me the most about the fossil fuel problem is that people don’t realize how many of the products that we rely on everyday relies on the same raw material. Moving electricity to renewable resources is easy; creating the required infrastructure without liquid hydrocarbons is currently impossible.

          1. Heather, I respectfully beg to disagree with you there. Moving electricity to solar (the only viable ‘renewable’ resource) is not so easy. Not really easy technically and way less politically.
            Note, the nastiest effect of fossil fuels is the CO2 (and sooth) they release when burned. The other products of fossil fuels appear relatively innocuous. So switching to solar for energy needs would really help.
            On another tack: will our children scold us for just *burning* such a valuable resource? In a Hummer, nogal!

            1. I agree that solar isn’t that easy, and would be a difficult transition, but there are others. We’re helped by our geography, but NZ is about 73% renewables and has been higher, mostly hydro-electric but also geothermal and wind. Solar is a very small part of it and is mostly just people with rooftop panels which heat their water. Government policy is 90% by 2025 and that’s easily on track.

              Waves are another option, but I understand that is very expensive and one that existed in Scotland has had to be closed down.

              There’s nuclear too though it’s not one that NZ uses and there’d be too much opposition I think if anyone tried. Our nuclear-free status is a big part of our identity. It’s why we’re not officially allies with the US.

              In 2015, 90% of the whole world’s new electricity generation was renewables, but I don’t know the breakdown into type.

              1. Nuclear power might make a comeback. There are new designs that use waste as fuel and are considered very safe. I think the political resistance might be the big stickler. Look at Japan.

              2. Not a chance. Utility scale solar is already cheaper than nuclear, and doesn’t have anywhere near the political opposition — never mind what you might think of the technological merits.



              3. I think you’re right. No matter how safe nuclear gets, there’s always going to be resistance. Countries like NZ and Japan that have a lot of earthquakes have an added dimension that makes the fear far more rational.

        3. “about the best anybody is actually doing is small training aircraft with well under an hour of endurance.”

          Perhaps you’re talking about somethng different, but a solar powered aircraft landed in California 5 days ago after a two and a half day flight across the Pacific.

          1. Solar Impulse is a fantastic project, but it’s got nothing whatsoever to do with commercial or even general aviation. It doesn’t even pretend to be something that you can load up with a family of 4 plus baggage for a weekend trip to the mountains — something even the nobly pedestrian Cessna 182 does with ease.



            1. Danger Will Robinson! Cessna’s are not all weather vehicles. When there’s weather, take the car.

              1. Cessnas can be flown safely through lots of weather, though they certainly have their limits. Icing is dangerous, and thunderstorms are always to be avoided. But normal rainy weather and the like isn’t a problem.



  4. Thanks for the post. I will archive it.

    It is definitely not inconceivable that a correction on the order of 10% of the accepted value of the origin of organic matter on earth existed. I am not a chemist, but I have seen a lot of Raman spectra for materials that are not even 40 years old and scientists debate (sometimes hotly) how the spectra can be interpreted.

    Lots of work ahead.

  5. When has a questionable conclusion ever been an obstacle to press coverage? I think this research is simply too abstract to be newsworthy (I think it’s great). If only they had included the “possibility” of the carbon coming from the tree of knowledge in the garden of Eden as an alternative hypothesis…

    1. I am there with you on that. My view right now is that I am not surprised of 4.1 byo life, but I like to let important new findings like this ‘ferment’ for a while before I open the bottle to celebrate.

  6. Presumably we may some day come to a finding where it really *is* ambiguous on whether it is before or after the “big event”. What is required for life in these origin studies? Cells?

    1. I admit I wish studies of this sort to include finding a boundary: old minerals with evidence of life, and somewhat older ones without such evidence.
      Now, different teams report cues of life even in the oldest specimens studied, which makes me wish a negative control.

      1. Good points!

        “What is required for life in these origin studies?”

        Defining life has not been easy and also not useful in fossil or emergence studies. It is easier to think of emergence as a process, and then to try to come up with tests.

        A very predictive and testable theory is my personal favorite because of that, vent theory. In that theory early cells were simply vent pores, It becomes recognizable darwinian as soon as the inherent vent RNA strand replication process were helped by ribozymes so it could diversify functional composition with local heredity over the pores.

        “makes me wish a negative control”.

        That is, it seems to me, theory dependent. For instance, if you look at vent theory *and* accept the minority position of O’Neill that the Nuvvuagittuq rocks are (slightly) older than the oldest zircon, they are a piece of crust that has never been subducted. (Which explains why it has no zircons and needed to be dated by an early radioactive series, and why it it is centered on the modern mixed mantle composition as it was original mantle melt.)

        No subduction means – I think – no serpentinization process possible from washing out of iron leaving the necessary alkaline rocks, as fresh mantle material moves away from spreading centers. Meaning no alkaline vents and so no life as of yet. E.g. an old enough rock with no zircons is your negative control in that theory.

  7. I am very gratified that you wrote about this. I’m sure I have splurged about the result already, but it bears repeating:

    This is the paleontological “WOW” signal! The size of the inclusions matches sediment captured prokaryotes, even though the paper doesn’t go into it.

    There are some other things of note.

    – The average organic δ13C is centered exactly on the one expected of photosynthetic metabolism.

    – The quality of the sparse data is already better – same scatter, more centered on the expected δ13C ration – than the 3.8 Ga data. Likely the difference between good closure and near metamorphic processes.

    – Hard work and likely capture rates. Less than 5 % of Jack Hill zircons is from the old subducted crust of interest, and of 10000 such zircons there was 1 carbon-bearing without fractures. That is far lower than the 4 % diamond inclusion false positives seen earlier. “… establishing a Hadean carbon cycle and its possible bearing on the origin of life will require enormous and sustained efforts.”

    The main argument against the 4 alternative abiotic processes known is that they are either known not to produce large inclusions (e.g Fisher-Tropfsch and similar processes) or should be rare (e.g. meteoritic carbon).

    – If this is a possible way to establish a firm signal for life, it is despite hard work a considerable shortcut to other approaches. I saw some group make preliminaries to study zircon formation conditions to see if it was possible to constrain to a biosphere (organic carbon cycle).

    I am less sure if it says something about the late bombardment impact rate. There is already models where prokaryotes easily survive 10 times what was thrown at them in spiked (“cataclysm”) variants of the Nice 1.0 planetary system formation models, and 30 times a spiked Nice 2.0 improved model. And people who claimed life would have started after a presumed cataclysm will continue to do so, in fact they already do.

    More interesting is that the entire zircon record is geared against cataclysms especially but also a less intensive, longer time late bombardment. Cavoise sees a lot of typical impact shock fractures in Vredesvort ~ 2 Ga zircons hundreds of kilometers out. But he can’t find a single such zircon within the Jack Hill archive, now up to 10 kcrystals at least. And there is no expectation (but of course not any test I know of yet) that subduction heals fractures that well. That is some tension between data and model!

    – They haven’t established context or repeatability.

    Since it is two similar size, similar isotope ration inclusions that would derive from subducted ocean floor sediments they arguably establish some context by themselves. See Valley’s 2015 review of 5000 [!] zircons establishing such subduction at the time. [ , Figure 17]

    And in a SETI Talk seminar about the find Bell notes that they have another fully encapsulated carbon sample under analysis. Its date is unknown however, so it may well be from the younger fraction of zircons, but would still show a repeatable phenomena. [ ]

    – Finally, I note that it is tentatively consistent with other data.

    I have noted that the Late Heavy Bombardment, if it happened, isn’t a problem. Valley’s 2015 review of 5000 [!] zircons show that Earth had habitable (non-boiling) oceans > 4.3 Ga. [Valley above, Figure 17]

    TimeTree has 3 references that all places the first observable split between bacteria, who photosynthesize, and archaea, that doesn’t, > 4.2 Ga. [ ]

    1. If I follow this, it could be that if carbon samples are found to be 4.2 or even 4.3 Ga, then these could well have the signature of carbon fixation.

      1. Sorry if it was a heavy read, but I am glad it promoted a response. (I have thought a lot on this find, obviously.)

        Carbon fixation would happen, but the Calvin cycle RuBisCO that gives the low and exact δ13C ratio would not be present before Archaea and Bacteria split, it is a Bacteria trait.

        Assuming TimeTree’s papers are correct, and the find certainly seems to shore them up, the range 4.3 – 4.2 Ga is possible. But 4.2 Ga would be more likely, even an ancient RuBisCO could be a complex protein as it is today. If we look at Valley’s data, 4.3 Ga is really the lower end of a habitable ocean. The oxygen ratio takes a dive if we look before that.

        Maybe 100 Myrs is much for RuBisCO evolution, it is a lot when we look at modern evolution. And there are signs in models of early protein folds that early evolution happened fast, genetic drift would have been the norm. And the long term trend has been that life evolved earlier than we thought.

        Still, it feels awkward to try to push the first known split up towards the beginning of Earth habitability. Maybe a balance of conservatism against the putative onslaught of revolutions is a good one.

  8. Putting this into perspective, the PNAS report suggests that as little as 0.3 billion years was required for life to brew up chemically on Earth, whereas it took another 4.1 billion years (more than 10 times longer) for that life, despite all the help of gods, fairies, and cosmic plans, to evolve into something we call intelligence. This suggests that life may be common on long-stable worlds with suitable conditions; intelligent life not so much.

    1. There is a book which discusses the probabilities of various significant transformations in life’s history. I can’t recall the name.
      They showed that stages, such as bacterial to eukaryote, transition to multicellular life, etc, seem to put limits on likelihood of advanced sentient life. Note too that we only have a few billion years for the sun to snuff the Earth. So, other planets would have to be quite lucky to duplicate our good fortune.

    2. I suspect that science-empowered intelligent life, being a product of Dawkinian natural selection and having at its disposal everything physics offers to bash each others heads, rarely endures for more than a few millennia. My evidence for this (and I confess my logic may be sloppy) is merely my personal experience that if human technological society will actually survive for many millennia, chances are I (or you) would have been born not far from a bullet-train station or spaceport, rather than into a world armed to its teeth, full of conflict, and ruled by sociopaths.

      1. Yes, your logic is faulty on a couple of counts.

        First, your birth date is not the outcome of some celestial lottery; it’s the result of a chain of physical events that happened at a specific place and time. Your chances of existing independent of that chain of events are nil. Other people exist at other points in time, but they’re not you, nor could you be them.

        But even if there were such a lottery, and you could have been born at any time in history, you’re trying to extrapolate from a single data point. The fact that you drew this particular birth date provides no information about how big the space of possible birth dates is.

  9. Very cool.

    My favorite fossil that we own (I think) is the 1.2 byo stromatolite fossil. It came from Australia as well. Talk about touching the deep past.

    1. The Jack Hill sedimentary rocks are very old and very processed. [ ]

      You may think that is a problem, but for the hardy zircons it is a boon. A few percent (< 5 %) are detrital ones that have been released by erosion from earlier subducted and then uplifted crust. They have blown free to be recaptured in JH sediments after several hundred million years, erosion tracks show that they have drifted that way. (And possibly some have been trough a sediment/erosion cycle several times.)

      I think there are other locales (South Africa's old cratons, I'm sure) with old zircons, but they are either rarer or not so researched yet.

    2. To give an image of the work necessary, I hear there are a few hundred of these, less than millimeter, small zircons in every cubic metre of rock. They have to be released by acid processing of the rocks.

      10 000 JH zircons means some 100 m^3 dug out and acidic dissolved rock…

  10. A question about fig. 2 up there: What is the blue hatched box around the central line of organic carbon? Is that the range of δ13C values of different sources of organic carbon?
    And by the way, what would be an example of inorganic carbon?

    1. Yes. Fractionation is different for different modes of photosynthesis – C4 plants have about -14 δ13C, C3 plants about -28 – and it increases along the food chain, resulting in that range.

      Our host is wrong, by the way: Atmospheric carbon has -7 δ13C, and is thus lower in carbon 12. The high carbon 12 values in organic matter come about because it’s easier to break the bounds of a molecule of CO2 containing carbon 12, so in photosynthesis, that type of CO2 is preferred.

    2. Carbon in carbon dioxide is inorganic, because there are no carbon-carbon bonds and no carbon-hydrogen bonds. Generally, we think of organic compounds as those with carbon-carbon bonds, but there are exceptions, like methane, which has carbon-hydrogen bonds and is chemically similar to other alkanes, all of which do have carbon-carbon bonds and are organic compounds.

      1. That is a description of what is ‘organic’ that I like. But I have seen text books that say CO2 is also organic, and it bugs me that they do that.

    3. “Inorganic” carbon is a misnomer, they mean abiotic carbon residues, which may have some organic bonds depending on origin process.

    1. Yes, those workers have pursued that hypothesis for a while. Maybe it is a way to save the tension between early zircons (with no impact fractures) and the late bombardment hypothesis (which relies on the shady state of the Apollo samples – contaminated by the last large impact or not?).

      Speaking of shade, the data used in this line of work (which is not the consensus, I take it) is shady. They identify less than 2 % of found zircons as produced in the last impact, and say the others are from older ones that happen to survive the impact. To me the data seem cherry picked and the model finetuned.

      The simplest explanation is that a few zircons are heavily damaged – isotope clock reset – by the impact. I dunno if they have a method to identify that doesn’t happen.

      And the work still doesn’t predict the absence of impact fractures in the oldest zircons, or the absence of zircons in the putatively oldest and never subducted crust we know. (If we trust O’Neill on the Nuvvuagittuq analysis, which itself is a minority opinion.)

      1. If you think I opinionate rather than read the papers on this hypothesis, you are correct. As long as it is a minority hypothesis, I can’t be arsed to study it. There is so much to study!

      2. Oh, I forgot that I browsed the paper enough to see that their old zircons lack the “just so” Ti signature that Valley’s old ones have. There is tension between the data sets!

  11. I wonder how future work will distinguish between the different possibilities: how to separate organic from meteorite origins etc

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