Gem from GK Chesterton

"A dead thing can go with the stream, but only a living thing can go against it."

From The Everlasting Man

Thursday, February 5, 2009

pL: The Persistence of Life

Last week somebody who was  important in my life passed away.  Among the swirling emotions attendant to funerals I've been thinking of life: its persistence, its fragility. This is the first of two companion pieces that looks at these thought lines, both striking in their own right, and even more so in apposition. 

This post takes up the first theme: life is unbelievably persistent. I'd like to look at the persistence of life from an unusual perspective*: the partial pressure of life.  Since the readers of TSON have already established the importance of semantics, let me define my terms.  The partial pressure of life can be thought of as the force that moves life from areas of high concentration to low concentration.  Not "Life Force" as in a nutritional drink, nor a Star Wars type force that lets Luke be a hero even though he starts out as a whiny little punk**.  Neither am I thinking about "life force" as a concept of spiritual energy.  

I'm using "partial pressure of life" in a similar manner that physicists talk about the partial pressure of dissolved   gases in a liquid.  Dissolved gases move from from areas of high partial pressures to low partial pressures.  I argue that the persistence of life stems from an analogous function (not identical, but analogous).  Life itself has a partial pressure and with often unrelenting, unstoppable force moves from areas of high concentration to low.  I'll shamelessly borrow from physics and refer to the partial pressure of life as pL (similar to pH, which is the partial pressure or activity of hydrogen dissolved in a fluid).   

OK, terms better defined, let's look at the persistence of life.  First, life has absolutely and completely blanketed the earth.   From the highest mountain to the deepest cavern.  Land, sea and air.  After learning about extreme life forms such as thermophiles, acidophiles, alkaliphiles, halophiles (and a whole other grocery isle of extreme "-ophiles") I'm more suprised to find a place where there isn't a form of life.

Of course, life is much more concentrated near the equator according to a number of metrics (diversity of species, number of individuals) and decreases toward the polar regions.   Using the digital equivalents of crayons, the partial pressure of life (pL) across the earth might be charted like this.

So the first thought for the persistence of life is from its geographic abundance.  Along the equator, where the earth receives the most sunlight exposure, the partial pressure of life is highest.   The number of species and variety is staggering (just in insects alone!).  Yet even at the poles, which have extreme temperature fluctuations and low amounts of nutrients, micro and macro psychrophilic*** life is abundant, though with a lower pL than the equator.    It would seem that the high pL gradient inexorably forces life from the equator to the poles.

In some cases there is an actual push from the areas of higher pL to lower pL.  Life is persistent because it fills voids.  Mount St. Helens is an excellent example of this.  On May 18th, 1980 the volcano erupted catastrophically, devastating over 200 square miles of wilderness.   It was a massive loss of life (both human and non-human) and within minutes the pL plummeted to near zero within the blast, avalanche and pyroclastic flow zone.  Yet because there was a drastic gradient in pL between the mountain and surrounding areas, life returned and persisted.   From both animal and plant re-colonization, life has returned to Mount St. Helens.  Life pushed from the high partial pressures surrounding the mountain into the void of the blast area.   

When describing the distribution of mountains and relief on the ground we use topographic lines and contours which are lines of equal elevation.  When describing the distribution of weather phenomenon we use both isotherms (lines of equal temperature) and isobarics (lines of equal barometric pressure).  When describing the devastation of Mount St. Helens, it is instructive (though not necessary) to use isobiotics**** (lines of equal pL).  If you would bear with me an another simple diagram, an isobiotic map after the blast would look something like this.

Even in a volcanic blast zone with, for all practical purposes, the annihilation of life, the steep gradient in the pL ultimately drove life in to fill the void at Mount St. Helens with both macro and micro-organism. The mountain hasn't fully recovered from the eruption. But it will.  Just as it has in millenia past.  Why?  Because life is shockingly resilient.

And Mount St. Helens is only a small volcano.  If you've been to eastern California, you know the stunning beauty of the Owens Valley.  If you haven't been, you must put it on your "List O' Amazing Places to Go".  Mt. Whitney and the Sierra Nevada are on the west and the White Mountains are on the east side of the valley. Drop dead gorgeous.  And yet, beginning about 30 million years ago, before the tallest mountains in the continental U.S. formed, everything did drop dead.  In his outstanding book Basin and Range, John McPhee tells it best:

Up through perhaps a hundred fissures, dikes, chimneys, vents, fractures came a violently expanding, exploding mixture of steam and rhyolite glass, and, in enormous incandescent clouds, heavier than air, it scudded across the landscape like a dust storm.  The volcanic ash that would someday settle down on Herculaneum and Pompeii was a light powder compared with this stuff, and as the great ground-covering clouds oozed into the contours of the existing landscape they sent streams hissing to extinction, and covered the stream beds and then the valleys, and--with wave after wave of additional cloud--obliterated entire drainages like plaster filling a mould.  They filled every gully and gulch, cave, swale, and draw until almost nothing stuck above a blazing level plain.  Needless to say, every living creature in the region died.  Single outpourings settled upon areas the size of Massachusetts, and before the heavy ash stopped flowing it had covered twenty times that.  Moreover, it was hot enough to weld...'When you bury a countryside in that much rock so hot it welds, that is the ultimate environmental catastrophe'.

Yet life now persists in the Basin Range--no, teems.   In fact, what is among the world's oldest living organisms, the 5,000 year old "Methuselah" Bristle Cone Pine tree, sits atop White Mountain along the Owens Valley.  Life not only prevailed, it's doing a funky chicken dance in the end zone. The partial pressure of life, applied over time can exert enormous force against even the most catastrophic conditions.  Ever forcing it's way down-gradient from "life" to "non-life". Here's a picture of a Bristle Cone Pine on White Mountain.

I love to backpack, especially in alpine wilderness.  I'm always stunned when I see a tree growing out of a hairline fracture of a rock like this.  This tree and its heirs (life) will likely prevail over the rock (non-life).  It's roots will dig deeper into the fissure and extend to depths of the rock where there is no life.  The roots will grow and ultimately crush the rocks into fragments.  Plants are an enormous and powerful erosional force, helping to reduce mountains to rubble (which is why JRR Tolkien had it exactly right in Lord of the Rings when the tree Ents attacked the fortress of Isengard and destroyed it's rocky reaches).

Though replicated on a smaller scale than the Basin and Range volcanism, the persistence of life is also on display at the Bikini Atoll in the south Pacific where 23 nuclear bombs were tested between 1946 and 1958. While residual radiation still persists, sea life has returned in abundance (including scuba divers), moving down the pL gradient from surrounding areas unaffected by the nuclear blasts.  It will continue to recover over time with life again trumping non-life.   

I'm also fascinated by the persistence of life throughout geologic time.  Newton's Ocean has a great post about telomerase and certain genes that appear to be immortal.  Also look at some cyanobacteria, such as stromatolites (pictured below), that are found both in the rock record dating back about 3 billion years ago and in modern day Australia.

Stromatolites (and other "living fossils") survived catastrophes that make the Bikini Atoll and even the Basin and Range volcanism seem like sand box playtime.  Consider the Permian/Triassic extinction about 250 million years ago where estimates of specie extinction rates are estimated to be between 70-90% of all marine life.  Likely tied to a planetary impact of sorts (asteroid, comet, etc..), the P/T event also wiped out a massive percentage of land-based species.   Another massive extinction occurred at the close of the Cretaceous about 65 million years ago, also likely related to planetary impact.

It becomes evident that pL gradients aren't operable just geographically, because when you look at the geologic record, you see the partial pressure of life acting across temporal gradients.  (I know that this is becoming a bit Rube Goldberg-ish, but it is my prerogative to make something simple more complex than it needs to.)

Extinction charts can be read as partial pressure of life charts (pL vs time).  If there is one thing that is explicitly clear from my study of geology, it is that "life" extends into "non-life" across time. Conditions change (often radically and catastrophically), eliminating a large portion of life, creating a steep pL gradient, then life moves down gradient and fills the void.

Looking forward, I believe the persistence of life is displayed as humans pursue space travel. There's an enormous partial pressure of life on earth adjoining a very low partial pressure of life in the rest of the solar system.  Life is bound to expand into the non-life of space.   

I'd like your thoughts on other examples of the persistence of life.  I know I've just scratched the surface*****.  Also 10 bonus points to the math whizz who comes up with a cool analysis for the partial pressure of life over time or space using calculus.  It starts with  dpL/dt or dpL/dx, now you do the rest if you want the BPs. 

For everybody clamouring that life is fragile (and I know you're out there... lurking!) that will covered in my forthcoming companion post.  For now, just sit and ponder the persistence of life.  Ahhh.....

The Fine Print
*It's unique to me either because I'm too lazy to look exhaustively elsewhere, or because this truly is an new perspective.  Perhaps I'll have Bob of Blackholes and Astrostuff do some digging.  He did after all assure me that my "nostril event horizon" phrase is unique.  And that's good enough for me.

**The "whiny little punk" characterization of Luke is unassailable.  Just watch the original movie (Episode 4 if you want to be technical).  Listen to him say, "But I wanted to go to Tarshi Station for some power converters" and you'll agree.  

***Of course I didn't know this word all by myself.  I found it like everybody else finds stuff.  And no, not the World Book Encyclopedia on my bookshelf.

****Bob, I'll need your help here also to confirm that nobody has coined this phrase.  Yes, I know, I'm in a bit of a slothful mood.   

*****Hey!  Look what I found beneath the surface... life!!!


  1. Ohh, physics! And differential equations! I'll have a go! Although I do have an unfair advantage, because I have just wrestled with cross-field diffusion of ions in plasmas for the last couple of weeks. But before I delve into the physics of ideal gases, three thoughts:

    i) You still have to define what your partial pressure of life is all about, i.e. what does it mean having more life in one place than in the other? Are you talking about biodiversity, i.e. the number of species per cubic metre (or per area)? Biomass?

    ii) If there was only the pL, then the earth would be filled up with life until there was no pressure gradient. There has to be a force acting on the species for your proposed distribution to exist - maybe we could call it environmental pressure?

    iii) I like your analogy (physics, yay!), but I think you can't take it too far - and this might be the reason it is not used by biologists. Life is much more complex than an ideal gas. For example, you can have a species suddenly dominating and eradicating concurrenting species, for example during an algal bloom. This is something that can't happen in a mixture of gasses (fortunately, or else you would have people suddenly keeling over because they ran into a bubble of CO2. Or spontaneously combusting because of a bubble of oxygen.... Hm... ).

    Anyway, back to the fun stuff - diffusion! The equations you were hinting at are called Fick's law, to the great amusement of germanophone physics-student's the world over. (see the translation for "ficken").
    Fick's first law governs the flux generated by a difference of (partial) pressures:
    J=-D grad(phi), or J=-D d(phi)/dx in one dimension, where J is the diffusive flux, D the the diffusion constant and phi the concentration of the substance in question.

    Fick's second law governs the change of the concentration in time:
    d(phi)/dt=D lap(phi), or d(phi)/dt=D d^2(phi)/dx^2 in 1D.
    Here D is again the diffusion coefficient and lap() is the laplace (grad squared). If this seems familiar, then you might know something about heat and heat-flow.

    Now you might ask, that is very well, but where does the pressure come in? You only talk about concentration here!

    To find the pressure we must take the gas-analogy further, and use the idael gas law, which is written (in familiar units) pV=nRT, where we find the pressure, p, the Volume V and the concentration n, as well as a constant R and the temperature T. But now we find us in hot water - what is the equivalent of the temperature in our analogy? In a gas temperature governs how fast the particles move, and it also tells us something of the energy inherent in the system. So..., ah, no idea. Maybe there is a biologist reading this who has an idea?

  2. Eh also, I am a cad.
    Stereotypical nerd behaviour, I am afraid: I got so fired up about my field that I forgot all about your loss - sorry about that, and my heartfelt condolences!

  3. I'm sorry to hear about your loss, Brian.

    I think that you have an interesting idea, but, like Boris, there are limits. One of the keys to the persistence of life is the mutability of life. The changes it has gone through are probably why it still exists and thrives. The distinction between types of life and actual mass is a key point.

    I was going to mention the life return to Hiroshima, but I don't know that that's more effective than the Bikini Atoll so I'm snookered. I'm sure that the Krakatoa remains are teaming with life and know that sunken ships become homes for even more and diverse life.

    Life, by it's nature, wants to survive. I see the analogy in space exploration myself and tend to agree in concept with your premise.

    Oh, and Luke, God, what a whiner! I wanted to kick him several times. It's why I like the second two better than the first.

  4. Boris, this is exactly what I was hoping for. I have an interest in applying math to things which don't appear to be suitable to math (see the Crayon Physics Paradox for another example). But this isn't a great quality for a guy who has a limited math background. So I'm leaning on folks like you to come through for me. And you did! (10 BPs!!!)

    Using Fick's first law, I imagine individual species having unique diffusion constants. For example, when I spray bleach on my kitchen counter top, I create a pL gradient, killing off many of the bacteria and molds within that space. Given different concentrations of molds and bacteria, I imagine that some species will colonize the area of low pL on the counter faster than others because of their higher diffusion constants. I will look at Fick's laws some more because that is exactly the type of thing I was hoping for. Thanks a truckload!

    Stephanie and Boris, you're both correct in that I've left "life" poorly defined. You're also both correct in that this pL concept can be taken too far. Before writing this post, I knew that I'd take this lump of dough and roll out until it's paper thin and holes break through. It's been a concept that I've been toying with for a while and I wanted to see how far I could push it. Even with limitations, I really enjoy the analogy to partial pressures of gases, so I busted out the big' ol' rolling pin and started flattening that analogy out to see how much area I could cover.

    As far as defining "life" goes, I actually think that pH is a suitable model. Acidity is a measure of the activity of hydrogen in a solution. Rather than narrowly define "life" I think the pL analogy works best by having "life" encompass all activity of all living organisms within an area (plant, animal, bacterial, etc...) Areas of low life activity are soon filled by diffusion from areas of higher activity. For now I want to include diversity and biomass within the definition of life activity. For this analogy I don't even really need to know what life is, exactly, just that there is "life" and "non-life" that create gradients by uneven distributions of life activity.

    Boris, your algae bloom example is great and still fits within the pL model. Just as external catastrophes or environmental pressures can form areas of low pL, there are times when pressures create a high pL, but ultimately the gradient forces prevail and the algae bloom can't sustain itself and the steep pL gradient becomes less steep by the life dieing. I see your point though about needing external pressures to form "concentrated pockets" of life such as the blooms.

    I'm wrestling with knowing what exactly the forces are at work (as are a million biologists, I'm sure). Stephanie, your comment "Life, by it's nature, wants to survive" is at the heart of it for me. What the heck is within "life" that always forces it to expand into non-life? It sure feels like a force to me, but what exactly that is moves into philosophy and theology rather quickly, which isn't my intention in this post (though I'm absolutely interested in the thoughts of others regarding this). The pL concept explains that life is persistent, but does nothing to explain why it is, or how it is, or even what life is. Nor was it intended to. I decided to take a small nibble on the topic rather than a huge, gobbling bite.

    There's lots of "life" left in this discussion and I hope it continues. It is a rich, rich subject that I want to continue.

  5. Thank you Boris and Stephanie for the consolations.

  6. Brian, I am so sorry for your loss, I'll be praying for you.

    You have such a unique way of looking at things and are very creative, never heard of the the partial pressure of life before this post,keep in mind my vocabuary, I use words like awesome and cool and awesomely cool, with the odd totally thrown in to make a point,lol. I, not being as slothful googled partial pressure of life and got your post,lol.

    ps, Luke=whiny

  7. Bob, thank you for your prayers. I'll take whatever I can get. Always.

    And I'm now dubbing you the TSON TACOS (Totally Awesome Checker Of Stuff) and throwing in 10 BPs for telling me what I want to hear. :-)

    The TACOS title bears a heavy burden. Think of Spider Man's uncle, "With great power comes great responsibility". It is your job to report that Google returned only one hit (or two at the most!) for an item, even if there are 12,000,000 items turned up in a search. Godspeed!

  8. Brian, I thought a bit more about your pL-idea over the week-end. It's very intriguing, because it is so very simple to model gases.
    If I understand you correctly, your model specifies a gas "type" for each species. The concentration would map to the species density in a given area, and the diffusion rate on the species mobility (plants - very low rate, birds - very high). You need a background medium to model no life - so the life-"gases" could be trace amounts in a nitrogen atmosphere.
    The problem with this analogy is that ideal gases (and real gases get awfully close to that in a diffusion context) don't interact - this is known as Dalton's Law and goes more or less like this: "The partial pressure of a gas in mixture is equal to the pressure of the same gas at the same temperature occupying the same volume." The reason for this is that gas molecules are so far apart - they don't "see" each other enough to influence to happen. In a simple gas model, the gas will expand until it fills the available volume, and after that nothing happens anymore - no hunter-predator analogy, no "algal bloom", no mountains with a harsher environment and less species.

    However, if we reduce our ambitions a bit, the model may still be useful. Let's take a simple lifeform, like a bacterium, and put it into a petri-dish. It will grow until it has filled the dish. Now replace the petri-dish with a (very) shallow bowl (only a couple of molecules high), and start filling it with a heavy gas from a thin tube - the gas will also expand until it fills the bowl and flows over the sides. It remains to prove that the expansion
    of the gas follows similar laws to the expansion of the bacteria. Since all I know about bacteria is that they are small, this exercise will be left to the reader...

    If this analogy works, then we can start modeling areas with less food in the petri-dish with bumps in the shallow bowl, where not as much gas can gather.

    And now to something completely different (secular content warning!):

    I wouldn't go as far as to ascribe a "force" to life's expansion - I rather think that what we see as a miracelous perseverance and pervasiveness of life is simply system-inherent emergent behaviour. Crystals will grow until they have filled all available space and/or used up all the available minerals. Life can go a step further, of course, by modifying its genetic code through mutation and selection and learning to consume resources that were not available before. (Have you read about the fungus growing inside the Chernobyl reactor, and actually using gamma radiation? Astounding!)
    But there doesn't have to be a force per se behind it, except of course the natural forces we know. Craig Venter has created the first synthetic bacterium genome, built wholly from scratch - the next step is inserting that genome into a bacterial shell and bringing it to life (cue lightning!). Nothing metaphysical here, which, in my humble opinion, makes the "miracle of life" even more awesome. Having a mysterious force animating life is well and good, but how great is it that life can exist without that mysterious force, just by immensly complicated chemistry, and we (well, Dr. Ventner) can build it? Stuff like that makes me which i'd gone into biochemistry or genetics!

  9. Boris, I agree that there are lots of ways where the analogy fails. I figure that if something can be represented by a single equation, such as Fick's Law, then it is not Life. Ecology must be an incredibly complex science with so many variables involved.

    But I'm intrigued that there appears significant similarity to partial pressures. In many regards the analogy works. My thinking gets kick-started sometimes by overlaying two systems that don't appear to have anything in common, then looking for commonalities. If you haven't done so, try an exercise of taking two widely different fields of study or disciplines and overlapping them then finding points of intersection. It is an excellent way to generate thought lines and helps get out of mental ruts.

    Going back to Fick's Law, it does seem to work well for simple, "closed" systems (such as your petri dish or my kitchen counter example). But if you apply it to Mount St. Helens, then the variables compound quickly. Nevertheless, I envision diverse life "activity" contributing to the diffusion constant including: reproduction rates of species, mobility of species (flying vs inch-worming), food consumption, predatory behaviors, cross-species interactions (bees/flowers, seeds/birds). When the sum of these activities across an are totaled, then Fick's diffusion constant starts to be identified (using what units I have no idea).

    I hadn't heard of the Chernobyl fungi! But now that I have, I can't say I'm surprised. I'm astonished, but not surprised. Give it another 50 years and higher order species will be living there because there's still probably a steep pL gradient and life persists!

    I also wished, at one point, to be a genetic engineer. Then I ran into an O-chem buzz saw in college that just chewed me up!


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