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A Longer Life for Earth’s Biosphere?

If we can find a way to double the lifespan of Earth’s biosphere, we’ll have changed the odds for finding extraterrestrial civilizations. After all, the amount of time an advanced culture can exist is one of the variables in the famous Drake equation, which estimates how many intelligent civilizations there are in the Milky Way. Lengthen potential habitability and you give any civilization that much more chance to spread into the cosmos.

Thus recent work out of Caltech intrigues us in several directions. Joseph Kirschvink and colleagues look at effects that could add a billion years on to our planet’s projected habitability. Consider: Earth took some four billion years to develop intelligent life, leaving us about a billion before our planet becomes uninhabitable. That result would be caused by a brighter and hotter Sun, the loss of carbon dioxide in the atmosphere through the weathering of rocks, and the eventual evaporation of water from the oceans, leaving nothing alive.

Reducing the amount of carbon dioxide in the atmosphere helps to ease the warming effect, and indeed, according to this Caltech news release, the pressure of carbon dioxide in the atmosphere has dropped 2,000-fold over the past 3.5 billion years, with man’s industrial activities serving to offset only a fraction of the decrease. Kirschvink believes “…we’re nearing the point where there’s not enough carbon dioxide left to regulate temperatures following the same procedures.” That points to a hot and uninhabitable future in a billion years or so.

Reducing atmospheric pressure could be a way around this outcome. The scientists say that removing massive amounts of molecular nitrogen, which already makes up 78 percent of the atmosphere, would allow us to regulate surface temperatures, ensuring that carbon dioxide will remain in the atmosphere and adding 1.3 billion years to Earth’s habitable life. It sounds like a science fictional solution relying on some vast future technology to re-tune the atmosphere, but Kirschvink’s team thinks the process may actually happen naturally.

After all, nitrogen is incorporated into the cells of growing organisms and gradually removed from the atmosphere as they die. Nitrogen reduction may be an ongoing process, suggesting that Earth’s atmospheric pressure may be lower now than in earlier epochs. One way to examine this, say the scientists, would be to study gas bubbles in ancient lavas, which could provide a reading on the change in atmospheric pressure over time.

Could exoplanetary studies give us clues to our own future? Grad student Kaveh Pahlevan, who worked with Kirschvink on this paper, sees a strong possibility:

“Hopefully, in the future we will not only detect earth-like planets around other stars but learn something about their atmospheres and the ambient pressures. And if it turns out that older planets tend to have thinner atmospheres, it would be an indication that this process has some universality.”

What would we do with an additional billion or so years of life? If technological civilizations are not in fact self-destructive, longer lifespans should give them a much greater chance of finding each other. The paper is Li et al., “Atmospheric Pressure as a Natural Regulator of the Climate of a Terrestrial Planet with Biosphere,” Proceedings of the National Academy of Sciences, published online June 1, 2009 (abstract).

Comments on this entry are closed.

  • John Hunt June 15, 2009, 15:49

    We are on the verge of establishing lunar outposts and have plans to move on to Mars. In a million, much less a billion years, we should be spread throughout the galaxy. What nature of atmosphere Earth has at that time will be fairly irrelevant.

  • philw1776 June 15, 2009, 15:55

    Clearly, articles like this are proof that we lack real understanding of how climate is regulated. The Earth has had CO2 levels tens of times higher during the time that animals have existed. There’s evidence that plants and crops perform better with higher levels of CO2. Most of the last 500 Myr, the Earth has been almost 10 deg C warmer and had no ice at its poles.


    I just wish we had the ability to image and analyze via spectroscopy ~100 other biosystem planets so we’d have some scientificly falsifiable idea of what we’re doing.

  • Alastair McKinstry June 15, 2009, 17:57

    Its well understood that CO2 levels have been higher; the trouble that Kirshvink and others (Lovelock, etc. ) point to is that solar output is increasing, and will weathering will draw down CO2 levels.

    Whats ignored in Kirshvinks analysis is clouds – it explicitly assumes a cloud-free atmosphere for simplicity. Increasing albedo can offset the increased solar input.

  • Dave Moore June 15, 2009, 18:39

    I think the roll Nitrogen has played in our climatic history has been under estimated. A thicker Nitrogen atmosphere would have warmed the young Earth through not only the adiabatic lapse rate but also through pressure broadening of the IR absorption lines of the atmosphere’s other constituents.

    Gerald Nordley calculated out the level of Nitrogen needed to maintain room temperatures through adibiatic pressure heating for various levels of insolation. Mars for instance would have a surface temperature simlar to Earth’s if it had 2.3 bar of Nitrogen in it’s atm.

    Like CO2, Nitrogen’s level in the atmosphere is the result of a dynamic balance in the geochemical cycle. In CO2’s case the balance of the cycle is heaverly tilted towards sequestration as carbonates so the atmospheric level is low. In Nitrogen’s case, the sequestration of Nitrogen as Nitrates and organic carbon is a lot slower and more nearly balanced by volcanic outgassing; nevertheless, the amount of Nitrogen sequested in our crust is twice the mass of that in our atmosphere.

    Early Earth, with its more vigorous volcanism would have certainly tilted the cycle in favor of a higher atmospheric pressure. Once life started fixing Nitrogen that would have drawn down the level, and once the atmosphere began to collect Oxygen, that would have resulted in a further reduction in Nitrogen levels over the eons from with Nitrates formed by lightening being sequestered.

    With Earths volcanisim winding down, I expect a gradual diminution in atmospheric Nitrogen levels.

    If there is a high variability in atmospheric Nitrogen levels of Earthlike planets, then the potential habitable zone will be considerably broadened.

  • ljk June 15, 2009, 21:11

    Doing the Math on Life


    By studying theories about why the universe is the way it is, mathematicians are hoping to uncover what these theories mean for the origin and future of life. Mathematics could be the key to answering some of life’s biggest questions, and could help astrobiologists understand life’s place in the universe.

  • Didac June 16, 2009, 2:40

    As John Hunt has put it, the question of time must be taken into account. Human species has been around for 2 million of years or so, and human technological civilization has been around for 50 years or so. Of course we cannot expect any closed and predetermined “destiny” or to assume an exponential expansion of (trans-)humankind. However, the “destiny” of the humankind would be surely decided in the next (very) few millenia.

    Said that, the relevance of Li et al. (2009) is that if Earth-like biospheres have habitability spans of 7-8 billions of years instead of 5-6 billions, we have a greater chance to find:
    – planets with “higher” (i.e. non-microorganismic) life forms.
    – planets with sentient species.
    Once a sentient species has developed into a “productive/technological” status, the question of time radically changes.

    Moreover, the question of time also affects the ideas exposed by philw1776. I am very skeptical of the kind of “environmental” governance that “world élites” try to impose in the pretense of anti-“global warming” fight. However, we have both a global warming trend in the decade-span and a Mya-span trend of CO2 reduction, and there is no contradiction in that.

  • keith June 16, 2009, 7:48

    I think it is pretty well known that atmospheric composition has varied significantly during the time Earth has born complex life-forms. In the Devonian period, the per cent oxygen was well above what it is now, that is how giant insects and spiders were viable life-forms at that time.

    I also remember something about atmospheric pressure at the time of the dinosaurs being significantly higher than it is now. That explains how pteradactyls managed to fly at all. This would back up the idea that atmospheres get thinner over time.

    However, I think these things are effects that depend on variables, like the amount of biomass, geological activity etc etc. If nitrogen was being buried, and not recycled over this long timescale, I think there would be much clearer evidence that it has happened in the geological record. I’ve never seen this being mentioned anywhere.

  • Adam June 16, 2009, 8:07

    Hi All

    The paper is up at the website of one of the authors – check my blog post for the link.

    The biosphere’s lifespan is doubled by the draw-down of nitrogen, reducing the pressure broadening of the CO2 spectral signature and thus reducing the greenhouse effect caused by the minimal 100 ppm of CO2 that the authors assume the biosphere needs. If we date the current aerobic biosphere from the late Proterozoic Oxygenation Event c. 635 Mya, then the new research means it ends after c. 3 billion years of life, rather than ~1.5 Gyr. But the end result is rather alien – the surface pressure drops to just 0.08 times the present before a runaway Greenhouse begins. That would be pretty challenging for most life on present day Earth and it would need to be mostly oxygen. The incident UV flux on the surface would be enhanced by such a thin atmosphere as would the cosmic-ray penetration to the surface – basically it’d be like living in the stratosphere. Hard to imagine what adaptations Life might adopt.

    What’s the minimum that our descendents – genetic or memetic – could do to preserve Life on Earth? There’s the classic paper by Fred Adams et. al. which uses a large asteroid as a gravitational energy transfer system between Earth and Jupiter/Saturn to pull Earth further out from the Sun over the next few billion years. That’s pretty serious astrophysical maneuvering and an error would mean a catastrophic impact.

    Personally I think the best approach is to change the insolation that actually reaches the surface by engineering the albedo. Then Earth would only need to be gently pushed out to about 1.15 AU to avoid tides dragging it into the Red Giant Sun. The Main Sequence lasts until the Sun is ~10 Gyr old, some 5.4 Gyr from now. Shifting Earth out to 1.15 AU means a delta-v of just 2 km/s – a force of just 71 billion newtons will be sufficient to move the Earth-Moon system over that distance in that time frame. Supplied via a solar-sail it’d need to be ~100,000 km across, yet it could be made very low-mass. At 0.005 kg/m^2 the sail would only mass 40 billion tons. Compared to the Earth-Moon system that’s insignificant.

    So how much light does the Earth need to reflect back into space? By the end of the Main Sequence the Sun’s output will only be ~1.8 times the present day, thus if Earth has a Bond albedo of 0.49 at 1.15 AU at that time, then it’ll remain at present day temperatures. It’s Bond albedo is currently 0.306 so it’s not a huge increase in reflectivity that’s required.

    Even off the Main Sequence the Sun’s output doesn’t violently rise for another ~billion years and only very briefly ascends to ~2700 times present day levels before hitting its Horizontal Branch, a fairly stable Helium Main Sequence for just 0.1 Gyr at ~50 times present insolation levels. If we could arrange to make Earth nearly perfectly reflective for a few million years, then it may survive.

    All assuming we don’t do something really drastic like pilot the Sun’s evolution…

  • Ronald June 16, 2009, 11:04

    I agree with John Hunt and Didac, that the lifespan of a sunlike star is fairly irrelevant once intelligent life and civilization arise. Even entire species and genera do not exist long enough to make any meaningful predictions concerning its persistence during such time periods. The next centuries or maybe millenia at the most will be decisive: either such a civilization manages to reach some kind of sustainability plus establish itself on several planetary systems to keep on evolving (and hence surviving in some form or another) or it will eventually disappear.

    What the habitable lifespan of a sunlike star is relevant for, however, is the timespan allowed for the rise and development of complex life. And maybe even, very speculatively, for the number of times that complex life and intelligence may arise (after major catastrophe).

    That is why I argued, in another thread, that the hotter sunlike stars (F9, G0) may be less suitable candidates for planets with complex life than the slightly cooler ones (around G5) and even less so than the coolest stars still considered sunlike (around K0, K1), although the narrower and more inward habitable zone may be another limitation in those cases.

    Without any tempering as described in this paper, our sun, a G2 star, will become too hot for (higher) life on earth at about (or just over) 5 gy, a ‘typical’ G0 star already around 4.5 gy, a ‘typical’ G5 star at around 5.5 gy, a K0 much (MUCH) later.

  • andy June 16, 2009, 18:08

    Pushes the possible lifetime around G-type stars into the domain where the cooling of the planet becomes a limiting factor.

  • Ronald June 17, 2009, 5:44

    @andy: at which age would cooling and resulting geological ‘death’ become a limiting factor for a roughly earthsized planet? And 2x, 3x?

    Would there be another (natural) way around this geological death and resulting deterioration of the atmosphere, for instance by some other way of recycling of necessary elements from the crust into the atmosphere?

  • philw1776 June 17, 2009, 9:29

    adam writes…”I think the best approach is to change the insolation that actually reaches the surface by engineering the albedo. ”

    Yes, insolation reduction is a far less risky and easier task than moving larrge asteroids over hundreds of millenia for even a modest space faring society. In the short run, a few hundred million years, we only need decrease insolation by a few % at most. Most insolation occurs at the equator where a synchronous orbit sunshade array could ‘eclipse’ portions of the sun and reduce insolation. Off topic, but such sunshades could double as photovoltiac power sources; efficiency would not matter much given the scale.

  • James M. Essig June 17, 2009, 14:10

    I am pleased with the potential doubling of the life expectancy of our biosphere. Perhaps techological intervention may enable the biosphere to survive until the onset of the solar red giant phase.

    One thing that I find extremely fascinating is the possible future forms that fauna on our planet may evolve into. Perhaps the potential medical science facilitated life expectancy increase of our species and the technological ability of making our human bodies more robust and able to withstand harsher conditions will permit us a longer civilization residency time on Earth.

    It is interesting to consider the life based aspects of our cosmos including biospheres. Perhaps due to artifacts left over from our religious heritage, we still tend to view life at least sub-consciously including human life as something not under the domain of natural science to the extent that stars, planets, black holes and the like are. However, perhaps a much better paradigm is to consider that life might and hopefully does develope unbiquituosly throughout the cosmos as a part of natural evolutionary processes. Life in some general sense of the word, seems to be just another aspect of the cosmos, just as mass, energy, space and time are. I hope that long lived biospheres are ubiquitous throughout the cosmos.

  • ljk June 17, 2009, 14:14

    Re-Engineering Earth

    Ideas: Energy & Environment July/August 2009 Atlantic

    As the threat of global warming grows more urgent, a few scientists are considering radical—and possibly extremely dangerous—schemes for reengineering the climate by brute force. Their ideas are technologically plausible and quite cheap.

    So cheap, in fact, that a rich and committed environmentalist could act on them tomorrow. And that’s the scariest part.

    by Graeme Wood


  • ljk July 13, 2009, 13:00


    Monday, July 13, 2009

    Causes and Timing of Future Biosphere Extinctions

    S. Franck, C. Bounama, and W. von Bloh

    Blog post by Will Baird

    Potsdam Institute for Climate Impact Research, Potsdam, Germany


    We present a minimal model for the global carbon cycle of the Earth containing the reservoirs mantle, ocean floor, continental crust, biosphere, and the kerogen, as well as the combined ocean and atmosphere reservoir. The model is specified by introducing three different types of biosphere: procaryotes, eucaryotes, and complex multicellular life.

    During the entire existence of the biosphere procaryotes are always present. 2 Gyr ago eucaryotic life first appears. The emergence of complex multicellular life is connected with an explosive increase in biomass and a strong decrease in Cambrian global surface temperature at about 0.54 Gyr ago.

    In the long-term future the three types of biosphere will die out in reverse sequence of their appearance. We show that there is no evidence for an implosion-like extinction in contrast to the Cambrian explosion. In dependence of their temperature tolerance complex multicellular life and eucaryotes become extinct in about 0.8–1.2 Gyr and 1.3–1.5 Gyr, respectively. The ultimate life span of the biosphere is defined by the extinction of procaryotes in about 1.6 Gyr.

    This is the paper[1] that is by and large the cornerstone of Ward’s book, The Medea Hypothesis. I’m chewing my way through what it means since I have finished the book. There are some troublesome assertions in there that I think ought to be brought a little more to light. I truly do not know how many people have been thinking about, commenting on, supporting or dismissing the whole Medea Hypothesis. So, I do know some of the paleo blog community reads here, so I’m going to air some thoughts and see where and what I get smacked for…or who has similar qualms. There will be a flurry of relatively light weight posts as something of a point, but point basis over the next week. I truly hope that I get some discussion going. If you are going to join in, grab the paper and read. Please.

    1. Available for free here. Hat-tip, Neil. Thank you.


    PS. The Medea Hypothesis actually counts as a YAGUMET. *sighs* We will not get to Ward’s Medea Hypothesis until at least Tuesday, possibly Wednesday. We’re going to go over Franck et al’s paper first. Without Franck et al’s paper, its model, and its conclusions, Ward’s stuff harder to grapple with: the book felt like there was a lot of assumption going on that we, the readers, were not privy to.