LIFE AS A MANIFESTATION OF THE SECOND LAW OF THERMODYNAMICS
ERIC D. SCHNEIDER National Ocean Service National Oceanic and Atmospheric Administration Washington, D.C., U.S.A.
JAMES J. KAY Environment and Resource Studies University of Waterloo Waterloo, Ontario, Canada, N2L 3G1 [email protected] www.fes.uwaterloo.ca/u/jjkay/
ABSTRACT We examine the thermodynamic evolution of various evolving systems, from primitive physical systems to complex living systems, and conclude that they involve similar processes which are phenomenological manifestations of the second law of thermodynamics. We take the reformulated second law of thermodynamics of Hatsopoulos and Keenan and Kestin and extend it to nonequilibrium regions, where nonequilibrium is described in terms of gradients maintaining systems at some distance away from equilibrium. The reformulated second law suggests that as systems are moved away from equilibrium they will take advantage of all available means to resist externally applied gradients. When highly ordered complex systems emerge, they develop and grow at the expense of increasing the disorder at higher levels in the system's hierarchy. We note that this behaviour appears universally in physical and chemical systems. We present a paradigm which provides for a thermodynamically consistent explanation of why there is life, including the origin of life, biological growth, the development of ecosystems, and patterns of biological evolution observed in the fossil record. We illustrate the use of this paradigm through a discussion of ecosystem development . We argue that as ecosystems grow and develop, they should increase their total dissipation, develop more complex structures with more energy flow, increase their cycling activity, develop greater diversity and generate more hierarchical levels, all to abet energy degradation. Species which survive in ecosystems are those that funnel energy into their own production and reproduction and contribute to autocatalytic processes which increase the total dissipation of the ecosystem. In short ecosystems develop in ways which systematically increases their ability to degrade the incoming solar energy. We believe that our thermodynamic paradigm makes it possible for the study of ecosystems to be developed from a descriptive science to a predictive science founded on the most basic principle of physics.
REFERENCE: Schneider, E.D, Kay, J.J., 1994, "Life as a Manifestation of the Second Law of Thermodynamics", Mathematical and Computer Modelling, Vol 19, No. 6-8, pp.25-48
© James J. Kay and Eric Schneider, 1992 INTRODUCTION Schrödinger solved this dilemma by turning In 1943 Erwin Schrödinger (1944) wrote to nonequilibrium thermodynamics, that is he his small book What is Life? , in which he recognized that living systems exist in a world attempted to draw together the fundamental of energy and material fluxes. An organism processes of biology and the sciences of stays alive in its highly organized state by physics and chemistry. He noted that life was taking energy from outside itself, from a larger comprised of two fundamental processes; one encompassing system, and processing it to "order from order" and the other "order from produce, within itself, a lower entropy, more disorder". He observed that the gene with it's organized state. Schrödinger recognized that soon to be discovered DNA, controlled a life is a far from equilibrium system that process that generated order from order in a maintains its local level of organization at the species, that is the progeny inherited the traits expense of the larger global entropy budget. of the parent. Schrödinger recognized that this He proposed that to study living systems process was controlled by an aperiodic crystal, from a nonequilibrium perspective would with unusual stability and coding capabilities. reconcile biological self-organization and Over a decade later these processes were thermodynamics. Furthermore he expected that uncovered by Watson and Crick. Their work such a study would yield new principles of provided biology with a framework that physics. allowed for some of the most important This paper takes on the task proposed by findings of the last thirty years. Schrödinger and expands on his However, Schrödinger's equally important thermodynamic view of life. We explain that and less understood observation was his "order the second law of thermodynamics is not an from disorder" premise. This was an effort to impediment to the understanding of life but link biology with the fundamental theorems of rather is necessary for a complete description of thermodynamics. He noted that at first glance, living processes. We further expand living systems seem to defy the second law of thermodynamics into the causality of the living thermodynamics as it insists that, within closed process and assert that the second law is a systems, entropy should be maximized and necessary but not sufficient cause for life itself. disorder should reign. Living systems, In short, our reexamination of thermodynamics however, are the antithesis of such disorder. shows that the second law underlies and They display marvelous levels of order created determines the direction for many of the from disorder. For instance, plants are highly processes observed in the development of ordered structures, which are synthesized from living systems. This work harmonizes physics disordered atoms and molecules found in and biology at the macro level and shows that atmospheric gases and soils. biology is not an exception to physics, we have simply misunderstood the rules of physics. Life and the Second Law 2
Central to our discussion is a fresh look at as open thermodynamic systems with a large thermodynamics. Since the time of Boltzmann gradient impressed on them by the sun. The and Gibbs there have been major advances in thermodynamic imperative of the restated thermodynamics especially by Carathéodory, second law is that these systems will strive to Hatsopoulos and Keenan, Kestin, Jaynes, and reduce this gradient by all physical and Tribus. We take the restated laws of chemical processes available to them. Thus thermodynamics of Hatsopoulos and Keenan ecosystems will develop structures and and Kestin and extend them so that in functions selected to most effectively dissipate nonequilibrium regions processes and systems the gradients imposed on them while allowing can be described in terms of gradients for the continued existence of the ecosystem. maintaining systems away from equilibrium. We examine one ecosystem closely and using In this context the second law mandates that as analyses of carbon flows in stressed and systems are moved away from equilibrium they unstressed conditions we show that the will take advantage of all means available to unstressed ecosystem has structural and them to resist externally applied gradients. Our functional attributes that lead to more effective expansion of the second law immediately degradation of the energy entrained within the applies to complex systems in nonequilibrium ecosystem. Patterns of ecosystem growth, settings unlike classical statements which are cycling, trophic structure and efficiencies are restricted to equilibrium or near equilibrium explained by this paradigm. conditions. Away from equilibrium, highly A rigorous test of our hypothesis is the ordered stable complex systems can emerge, measurement of reradiated temperatures from develop and grow at the expense of more terrestrial ecosystems. We argue that more disorder at higher levels in the system's mature ecosystems should degrade incoming hierarchy. solar radiation into lower quality exergy, that is We will demonstrate the utility of these have lower reradiated temperatures. We then restatements of the second law by considering provide data to show that not only are more one of the classic examples of dissipative mature ecosystems better degraders of energy structures, Bénard Cells. We argue that this (cooler) but that airborne infrared thermal paradigm can be applied to physical and measurements of terrestrial ecosystems may chemical systems, and that it allows for a offer a major breakthrough in providing thermodynamically consistent explanation of measures of ecosystem health or integrity. the development of far from equilibrium complex systems including life. CLASSICAL THERMODYNAMICS As a case study we focus on the Because the basic tenets of this paper are applications of these thermodynamic principles built on the principles of modern to the science of ecology. We view ecosystems thermodynamics, we start this paper with a
by Eric Schneider and James Kay Life and the Second Law 3
brief discussion of thermodynamics. We ask that although the total quantity of energy in a the reader who is particularly interested in closed system will remain unchanged, the ecology to bear with us through this quality of the energy in the system (i.e the free discussion, because an understanding of these energy or the exergy content) may change. aspects of thermodynamics will make much of The second law requires that if there are our discussion of ecology self-evident. For the any physical or chemical processes underway reader who has mastered thermodynamics we in a system, then the overall quality of the believe that our approach to the theoretical energy in that system will degrade. The second issues of nonequilibrium thermodynamics is law of thermodynamics arose from Carnot's original and permits a more satisfactory experiments with steam engines and his discussion of observed far from equilibrium recognition that it was impossible to convert all phenomena. the heat in such a system completely to work. Comparatively speaking, thermodynamics His formal statement of the second law may be is a young science but has been shown to apply stated as: It is impossible for any system to to all work and energy systems including the undergo a process in which it absorbs heat classic temperature-volume-pressure systems, from a reservoir at a single temperature and chemical kinetic systems, electromagnetic and converts it completely into mechanical work, quantum systems. The development of while ending at the same state in which it classical thermodynamics was initiated by began. The second law notes that work may be Carnot in 1824 through his attempts to dissipated into heat, whereas heat may not be understand steam engines. He is responsible converted entirely into work, thus proving the for the notion of mechanical work, cycles, existence of irreversibility in nature. (This was reversible processes, and early statements of a novel, paradigm shattering suggestion for its the first and second law. Clausius in the period time.) 1840 to 1860 refined Carnot's work, The second law can also be stated in terms formalizing the first and second law and the of the quantitative measure of irreversibility, notion of entropy. entropy. Clausius discovered that for any cyclic The first law arose from efforts to process1: understand the relation between heat and work. ⌡⌠dQ/T ≤ 0 Most simply stated, the first law says that energy cannot be created or destroyed and that where equality holds only for reversible despite the transformations that energy is processes (for example, a Carnot cycle). constantly undergoing in nature (i.e. from heat to work, chemical potential to light), the total energy within a closed or isolated system 1Where Q is heat transfer in calories and T is in degrees Kelvin remains unchanged. It must be remembered
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Clausius, borrowing from the Greek for of the ten compartments and the rest of the transformation, called the quantity ⌡⌠-dQ/T compartments being empty. If doors are opened between the compartments and the box which measures the irreversibility of a process, is subjected to a pattern of random shaking one the "entropy" of the process. The second law would expect, over time, to see a distribution can be stated as: any real process can only of about 1,000 marbles per compartment, the proceed in a direction which results in an distribution which has the largest number of entropy increase. This universal increase in possible microstates. This randomization of entropy draws the "arrow of time " (Eddington, the marbles to the equiprobable distribution 1958) in nature and represents the extent to corresponds to the macrostate with the which nature becomes more disordered or maximum entropy for the closed system. If random. one continued the shaking it would be highly All natural processes can be viewed in light improbable but not impossible for all the of the second law and in all cases this one- marbles to reseparate themselves into the low sided aspect of nature is observed. Heat entropy configuration with 10,000 marbles in always flows spontaneously from a hotter one compartment. The same logic is applied reservoir to a colder reservoir until there is no by Boltzmann to explain the macroscopic longer a temperature difference or gradient; gas phenomena of thermodynamics in terms of will always flow from high pressure to low microstates of matter. Systems will tend to the pressure until there is no longer a pressure macrostate which has the largest number of difference or gradient. If one mixes hot and corresponding accessible microstates. cold water, the mixture comes to a uniform temperature. The resulting luke warm water THE EXTENDED LAWS OF THERMODYNAMICS will not spontaneously unmix itself into hot and In 1908 thermodynamics was moved a step cold portions. Boltzmann would have restated forward by the work of Carathéodory (Kestin, the above sentence as: it is highly improbable 1976) when he developed a proof that showed that water will spontaneously separate into hot that the law of "entropy increase" is not the and cold portions, but it is not impossible. general statement of the second law. The more Boltzmann recast thermodynamics in terms encompassing statement of the second law of of energy microstates of matter. In this thermodynamics is that "In the neighbourhood context, entropy reflects the number of of any given state of any closed system, there different ways microstates can be combined to exists states which are inaccessible from it give a particular macrostate. The larger the along any adiabatic path reversible or number of microstates for a given macrostate, irreversible". This statement of the second the larger the entropy. Consider a ten law, unlike earlier ones, does not depend on compartment box with 10,000 marbles in one the concepts of entropy or temperature and
by Eric Schneider and James Kay Life and the Second Law 5 applies equally well in the positive and negative 1977, 1989). These systems are open and are temperature regimes. moved away from equilibrium by the fluxes of More recently Hatsopoulos & Keenan material and energy across their boundary. (1965) and Kestin (1966) have put forward a These systems maintain their form or structure principle which subsumes the 0th, 1st and 2nd by continuous dissipation of energy and thus Laws: "When an isolated system performs a are known as dissipative structures. Prigogine process after the removal of a series of internal showed that nonequilibrium systems, through constraints, it will reach a unique state of their exchange of matter and/or energy with the equilibrium: this state of equilibrium is outside world, can maintain themselves for a independent of the order in which the period of time away from thermodynamic constraints are removed". (This is called the equilibrium in a locally reduced entropy steady- Law of Stable Equilibrium by Hatsopoulos & state. This is done at the cost of increasing the Keenan and the Unified Principle of entropy of the larger "global" system in which Thermodynamics by Kestin.) the dissipative structure is imbedded; thus The importance of this statement is that, following the mandate of the second law that unlike all the earlier statements which show that overall entropy must increase. Nonliving all real processes are irreversible, it dictates a organized systems (like convection cells, direction and an end state for all real processes. tornados and lasers) and living systems (from All previous formulations of the second law cells to ecosystems) are dependent on outside tells us what systems cannot do. This energy fluxes to maintain their organization in a statement tells us what systems will do. An locally reduced entropy state. example of this phenomena are two flasks, Prigogine's description of dissipative connected with a closed stopcock. One flask structures is formally limited to the holds 10,000 molecules of a gas. Upon neighbourhood of equilibrium. This is because removing the constraint (opening the stopcock) his analysis depends on a linear expansion of the system will come to its equilibrium state of the entropy function about equilibrium. This is 5,000 molecules in each flask, with no gradient a severe restriction on the application of his between the flasks. These principles hold for theory and in particular precludes its formal closed isolated systems. However a more application to living systems. interesting class of phenomena belong to To deal with the thermodynamics of systems that are open to energy and/or material nonequilibrium systems, we propose the flows and reside at stable states some distance following corollary that follows from the proof from equilibrium. by Kestin of the Unified Principle of These much more complex thermodynamic Thermodynamics. His proof shows that a systems are the ones investigated by Prigogine system's equilibrium state is stable in the and his collaborators (Nicolis and Prigogine, Lyapunov sense. Implicit in this conclusion is
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that a system will resist being removed from becomes more and more difficult to move the the equilibrium state. The degree to which a system away from equilibrium (that is, system has been moved from equilibrium is proportionally more available work must be measured by the gradients imposed on the expended for each incremental increase in system. "The thermodynamic principle gradient as the system gets further from which governs the behaviour of systems is equilibrium, i.e. ∆T increases). that, as they are moved away from In chemical systems, LeChatelier's equilibrium, they will utilize all avenues principle is another example of the restated available to counter the applied gradients. second law. Fermi, in his 1936 lectures on As the applied gradients increase, so does thermodynamics, noted that the effect of a the system's ability to oppose further change in external conditions on the movement from equilibrium." equilibrium of a chemical reaction is prescribed (In the discussion that follows we shall by the LeChatelier's principle. "If the external refer to this statement as the "restated second conditions of a thermodynamic system are law". The pre-Carathéodory statements (i.e. altered, the equilibrium of the system will tend entropy will increase) will be referred to as the to move in such a direction as to oppose the classical second law) change in the external conditions" (Fermi, A simple example of this phenomena is the 1956). Fermi noted that if a chemical reaction Bénard cell. The experimental apparatus for were exothermal, i.e. (A+B=C+D+heat) an studying the Bénard cell consists of a highly increase in temperature will shift the chemical instrumented insulated container enclosing a equilibrium to the left hand side. Since the fluid. The bottom of the container is a heat reaction from left to right is exothermal, the source and the top is a cold reservoir. (See displacement of the equilibrium towards the left Figure 1.) When the fluid is heated from results in the absorption of heat and opposes below it resists the applied gradients (∆T) by the rise in temperature. Similarly a change in dissipating heat through conduction. As the pressure (at a constant temperature) results in a gradient is increased, the fluid develops shift in the chemical equilibrium of reactions convection cells. These convection cells which opposes the pressure change. increase the rate of dissipation. (These Thermodynamic systems exhibiting convection cells are called Bénard cells, temperature, pressure, and chemical Chandrasehkar, 1961.) equilibrium resist movement away from these Figure 2-c shows a plot of the gradient (Ra, equilibrium states. When moved away from the Rayleigh number, which is proportional to their local equilibrium state they shift their state the gradient ∆T) against the available work in a way which opposes the applied gradients which is expended in maintaining the gradient. and moves the system back towards its local The dynamics of the system are such that it equilibrium attractor. The stronger the applied
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gradient, the greater the effect of the through fluctuations, small instabilities which equilibrium attractor on the system. lead to irreversible bifurcations and new stable The reason that our restatement of the system states. Thus the future states of such second law is a significant step forward for systems are not deterministic. Dissipative thermodynamics is that it tell us how systems structures are stable over a finite range of will behave as they are moved away from conditions and are sensitive to fluxes and flows equilibrium. Implicit in this is that this from outside the system. Glansdorff and principle is applicable to nonequilibrium Prigogine (1971) have shown that these systems, something which is not true for thermodynamic relationships are best classical formulations of the second law. represented by coupled nonlinear relationships In particular our "restated second law" i.e. autocatalytic positive feedback cycles, avoids the problems associated with state many of which lead to stable macroscopic variables such as entropy which are only structures which exist away from the defined for equilibrium. Our restatement of the equilibrium state. Convection cells, hurricanes, second law sidesteps the problems of defining autocatalytic chemical reactions and living entropy and entropy production in systems are all examples of far-from- nonequilibrium systems, an issue that has equilibrium dissipative structures which exhibit plagued nonequilibrium thermodynamics for coherent behavior. years. By focusing on gradient destruction, we The transition in a heated fluid between avoid completely the problems encountered by conduction and convection is a striking Prigogine (1955), and more recently Swenson example of emergent coherent organization in (1989), who use extremum principles based on response to an external energy input. A the concept of entropy to describe self- thorough analysis of these simple physical organizing systems. Nonequilibrium systems systems has allowed us to develop some can be described by their forces and requisite general thermodynamic principles applicable to flows using the well developed methods of the development of complex systems as they network thermodynamics (Katchalsky and emerge at some distance away from Curren, 1965, Peusner, 1986, and Mikulecky, equilibrium. Bénard, Rayleigh, (see 1984). Chandrasekhar, 1961), Silveston (1957) and Brown (1973) conducted carefully designed DISSIPATIVE STRUCTURES AS GRADIENT experiments to study this transition. DISSIPATORS In this section we examine the behaviour of dissipative structures in light of the restated second law. Prigogine and his colleagues have shown that dissipative structures self-organize
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The System FIGURE 1: Bénard Cells
Colld Siink Schematics of the Bénard cell apparatus (top schematics, Q=heat transfer) and Q Working Fluid temperature profiles (lines inside apparatus in Heatt Source middle and bottom schematics, h = height) in the working fluid before and after the transition to convection. The fluid is heated from below and the top of the apparatus acts as a cold sink. Initially all dissipation through the fluid occurs via conduction and molecule to molecule Conduction interaction. When the gradient reaches a critical Colld Siink level (Rayleigh number 1760) the transition to highly organized convection occurs. h As the gradient is increased it becomes Heatt Source harder and harder (more work is required) to maintain the higher rate of dissipation (see Temperature Figure 2). The further the system is moved away from its equilibrium state the more exergy is destroyed, the system produces more entropy, and more work is required to maintain it in its nonequilibrium state. Convection Due to the convective overturn most of the
Colld Siink working fluid in the container becomes Boundary Layer vertically isothermal (with little gradient) and h only the boundary layers on the edge of the Boundary Layer Heatt Source system carry the gradient. As the gradient is increased the boundary layers become thinner Temperature and more dissipation occurs.
Definitions: Nusselt Number: Nu = Q / (k ∆T / h) Rayleigh Number: Ra = g α ∆T h3 / κ ν
where Q=heat flow, k=coefficient of heat conduction, T=temperature, h=depth, g=gravity, α=coefficient of volume expansion, κ=coefficient of thermometric conductivity, ν=coefficient of kinematic viscosity.
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Heat Dissipation Rate (W) vs Gradient (Ra) FIGURE 2.
50 These graphs are calculations by us of entropy production and exergy destruction 40 Total during heat transfer across a fluid. The data used is from the classic experiments of 30 Silveston (1957). A fluid is heated from
W below. The temperature difference between the 20 top and bottom of the fluid is increased and the 10 heat transfer from the bottom to the top is Conduction Only recorded. At a Rayleigh number (a 0 dimensionless measure of gradient) of about 1000 2000 3000 4000 5000 6000 1760 Bénard Cells appear, that is convection Ra starts. As the Rayleigh number (temperature difference) increases convection becomes the dominant mode of heat transfer. The particular analysis is for Silicon 350 at Entropy Production Rate (P) vs Gradient (Ra) a depth of 6.98 mm. with a surface area of 0.0305 sq. m.. The first graph is the heat 0.025 transfer rate (Kcal/Hour) across the fluid as a 0.020 function of Rayleigh number (temperature difference). The bottom curve is the heat Total 0.015 transfer rate without Bénard Cells and the top
P curve is the heat transfer rate with the formation 0.010 of Bénard Cells. The point is that the emergence of the ordered structure (Bénard 0.005 Conduction Only Cells) dissipates more energy. The second graph is of entropy production 0.000 ° 1000 2000 3000 4000 5000 6000 rate (Kcal/Hour/ K) versus Rayleigh number (the gradient). Again we see the emergence of Ra the ordered structure results in more entropy production. The third graph shows the available work1 (exergy) (Kcal/hour) which must be provided from an external source in order to maintain the gradient. As the gradient Exergy Destruction Rate (Ø) vs Gradient (Ra) increases a greater amount of work must be done to incrementally increase the gradient. It 7 becomes more difficult to maintain the gradient 6 as the system becomes more organized. 5 4 Total Ø 3 2 1 Conduction Only 0 1000 2000 3000 4000 5000 6000 Ra 1Exergy/Availability: A measure of available work content of energy.(Brzustowski and Golem, 1978, Ahern 1980, Moran, 1982) It is a measure of the potential of energy to perform useful work. It reflects the quality of the energy. Irreversible processes destroy exergy.
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The lower surface of the experimental increases it becomes harder to increase the apparatus is heated and the upper surface is gradient. kept at a cooler temperature. (See Figure 1). Initially the temperature gradient in the Hence a temperature gradient is induced across apparatus is being accommodated solely by the fluid. The initial heat flow through the random conductive activity. When the gradient system is controlled by conduction. Energy is raised, a combination of factors including transfer is by molecule to molecule interaction. surface tension effects and gravitational fluid When the heat flux reaches a critical value of instability, converts the system to a mixed the temperature gradient, the system becomes conductive-convective heat transfer system. unstable and the molecular action of the fluid The transition to coherent behaviour occurs at becomes coherent and convective overturning Ra=1760 (see definitions, Figure 1). emerges. These convective structures result in Figure 2 are plots of Silveston's original highly structured coherent hexagonal surface data using silicon as the working fluid with a patterns (Bénard Cells) in the fluids. This separation between the hot and cold sinks of coherent kinetic structuring increases the rate of 6.98 mm. The curve labelled "Conduction" is heat transfer and gradient destruction in the the dissipation which would occur without the system. emergent coherent behaviour. The difference This transition between noncoherent, between the curve labelled "Total", and the one molecule to molecule, heat transfer to coherent labelled "Conduction", is the increase in structure results in excess of 1023 molecules dissipation due to the emergence of the acting together in an organized manner. This dissipative structure. As is shown in Figure 2, seemingly improbable occurrence is the direct with the onset of convection there is a dramatic result of the applied temperature gradient and is increase in the heat transfer rate across the the system's response to attempts to move it system. away from equilibrium. From the literature, especially Recently we studied the Bénard Cell Chandrasekhar (1961), and from our analysis phenomena in detail, using the original data of Silveston and Brown's data we note the sets collected by Silveston (1957) and Brown following behavior for these systems: (1973) (which they most graciously provided 1) Heat Dissipation Rate (transfer of heat us with). We believe that these analyses are between the plates) is a linearly increasing significant, in that we have calculated for the function of the gradient ∆T (see figure 2-a, first time the entropy production, exergy drop recalling that Ra is proportional to ∆T). and available work destruction, resulting from 2) Entropy production rate (P) vs ∆T increases these organizing events. (See Figure 2.) Our in a nonlinear way (see figure 2-b). analysis clearly shows that as the gradient
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3) Exergy destruction rate (Ø) vs ∆T increases equal to the increase in degradation at any in a nonlinear way, the shape of the curve point due to the emergent process. This is being the same as P vs ∆T. true for any process which involves only 4) 2&3 imply that as the gradient increases it heat transfer. Otherwise degradation ≠ is harder (requires more available work, dissipation. (This is why Prigogine at that is exergy) to incrementally increase the times mistakenly uses these terms gradient. The further from equilibrium that interchangeably.) the system is, the more it resists being 9) The principle governing these systems is moved further from equilibrium. In any not one of maximum entropy production real system there is an upper limit to the but rather one of entropy production change gradient which can be applied to the being positive semi-definite as you increase system. the gradient. See point 7 above. The 5) Once convection occurs, the temperature interesting question is, how much structure profile within the fluid is vertically emerges for a given gradient, and how isothermal outside the boundary layer, i.e. much resistance exists to increasing the the temperature in the convection cells is gradient further. constant thus effectively removing the As the temperature difference increases, there gradient through most of the fluid (see are a number of further transitions at which the Figure 1). hexagonal cells re-organize themselves so that 6) As the gradient increases, further critical the cost of increasing the temperature gradient points are reached. At each critical point escalates even more quickly. Ultimately the the boundary layer depth decreases. system becomes chaotic and dissipation is 7) 1 is true because the rate of heat transfer is maximum in this regime. controlled (more or less) by the rate of heat The point of this example is that in a simple flow across the boundary layer, i.e. by physical system, new structures emerge which conduction which is a linear process. This better resist the application of an external process is also responsible for most of the gradient. The Bénard cell phenomena is an entropy production, as there will be little excellent example of our nonequilibrium production due to convection. The slope restated second law. As we will see later, other change is caused by the decrease in the physical, chemical, and living systems observe boundary layer depth (l) at a mode change similar rules. (critical point). (Recall Q=k∆T/l thus as l The more a system is moved from decreases, slope (k/l) increases.) equilibrium, the more sophisticated its 8) Nu is Q/Qc = P/Pc = Ø/Øc; that is, in mechanisms for resisting being moved from Bénard Cells, the increase in dissipation at equilibrium. This behaviour is not sensible any point due to the emergent process is from a classical second law perspective, but is
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what is expected given the restated second law. upper bottle filled with water and the lower No longer is the emergence of coherent self- bottle empty. When set vertical, a thirty organizing structures a surprise, but rather it is centimeter gradient of water exists. an expected response of a system as it attempts Due to the orifice configuration, the bottle to resist and dissipate externally applied drains slowly requiring approximately six gradients which would move the system away minutes to empty the upper bottle (i.e. to from equilibrium. The term dissipative reduce the gradient in the system). The structure takes on a new meaning. No longer experiment is then repeated with the bottles does it mean just increasing dissipation of being given a slight rotational perturbation. A matter and energy, but dissipation of gradients vortex forms, driven by the gravitational as well. gradient within the system, and drains the In this regard it is important to distinguish upper bottle in approximately 11 seconds. The between energy dissipation and energy "tornado", a highly organized structure, has the degradation. Dissipation of energy means to ability to dissipate the gradient much faster thus move energy through a system, as in the bringing the system to its local equilibrium Bénard cell. Dissipation may or may not more quickly! Here again is a manifestation of destroy gradients. Degradation of energy the restated second law, a macroscopic highly means to destroy the ability of energy to set up organized structure of 1023 molecules acting gradients. The ability to set up gradients is coherently to dissipate a gradient. The measured by the availability or exergy of the production of the highly organized system, the energy. Thus energy degradation means tornado, leads to more effective dissipation of exergy destruction, that is the degradation of the larger driving gradient, the gravitational the ability of the energy to produce gradients differences in water levels between the bottles. that can accomplish work. In simple systems As in the Bénard convection experiments, involving only heat flow, energy degradation is organized structures reduce gradients more via energy dissipation. quickly than random linear processes. The gradient reducing nature of self- It should not be surprising that this simple organizing systems is dramatically experimental device mimics meteorological demonstrated by a simple experimental device phenomena such as mesoscale weather sold as a toy in a nationwide scientific catalog patterns. The development of temperature (Edmunds). Their "Tornado in a Bottle" (not gradients between a warm earth and a cooler to be confused with "fusion in a bottle"), overlying atmosphere results in highly consists of a simple plastic orifice that allows organized convective cloud patterns which the connection of two 1.5 liter plastic soda reduce the troposphere temperature gradient. bottles end to end. The bottles are connected The violent destructive power of tornadoes is a and set on a level surface to drain with the manifestation of the ability of these self-
by Eric Schneider and James Kay Life and the Second Law 13
organizing structures to rapidly dissipate strong examples of which are found in simple temperature and barometric gradients. inorganic chemical systems, in protein Hurricanes are another example of mesoscale synthesis reactions, or phosphorylation, dissipative meteorological structures. polymerization and hydrolytic autocatalytic The global weather, wind and ocean reactions. circulation patterns are the result of the Autocatalytic reactions systems are a form difference in heating at the equator relative to of positive feedback where the activity of the the poles. The general meteorological system or reaction augments itself in the form circulation of the earth, although affected by of self-reinforcing reactions. Consider a spatial, coriolis and angular momentum effects, reaction where A catalyzes the formation of B is driven by gradients and the global system's and B accelerates the formation of A; the attempt to dissipate them and come to local overall set of reactions is an autocatalytic or equilibrium. Paltridge (1979) has suggested positive feedback cycle. Ulanowicz (1986) that the earth-atmosphere, climate system notes that in autocatalysis, the activity of any configures itself into a state of maximum element in the cycle engenders greater activity dissipation and that the global distribution of in all the other elements, thus stimulating the clouds, temperature and horizontal energy aggregate activity of the whole cycle. Such flows are governed by thermodynamic self-reinforcing catalytic activity is self- dissipative processes similar to those described organizing and is an important way of above. We see that the earth-climate system, as increasing the dissipative capacity of the well as other dissipative systems, do not reach system. Cycling and autocatalysis is a a static equilibrium state because they are open fundamental process in nonequilibrium thermodynamic systems constantly receiving a systems. supply of external energy (i.e. from the sun), The notion of dissipative systems as which drives them and maintains them in a gradient dissipators holds for nonequilibrium nonequilibrium organized state. physical and chemical systems and describes So far we have focused our discussion on the processes of emergence and development of simple physical systems and how complex systems. Not only are the processes thermodynamic gradients drive self- of these dissipative systems consistent with the organization. The literature is replete with restated second law, it should be expected that similar phenomena in dynamic chemical they will exist wherever there are gradients. systems. Prigogine and the Brussel's School and others have documented the LIVING SYSTEMS AS GRADIENT DISSIPATORS thermodynamics and behavior of these We will now focus our attention on the role chemical reaction systems. Chemical gradients of thermodynamics in the evolution of living result in dissipative autocatalytic reactions, systems. The father of statistical
by Eric Schneider and James Kay Life and the Second Law 14 thermodynamics, Boltzmann recognized the struggle for entropy, which becomes apparent contradiction between the available through the transition of thermodynamically predicted randomized cold energy from the hot sun to the cold death of the universe and the existence of a earth. In order to exploit this transition process (i.e. life) in nature by which systems as much as possible, plants spread their grow, complexify, and evolve, all of which immense surface of leaves and force the reduce their internal entropy. As early as 1886 sun's energy, before it falls to the Boltzmann observed that the gradient on earth, earth's temperature, to perform in ways caused by the energy provided by the sun, yet unexplored certain chemical drives the living process and suggested a syntheses of which no one in our Darwinean like competition for entropy in laboratories has so far the least idea. living systems: The products of this chemical kitchen "Between the earth and sun, constitute the object of struggle of the however, there is a colossal temperature animal world." (Boltzmann, 1886). difference; between these two bodies As we noted in the introduction energy is thus not at all distributed Boltzmann's ideas were further explored by according to the laws of probability. Schrödinger in "What is Life?" (Schrödinger, The equalization of temperature, based 1944). Schrödinger, like Boltzmann, was on the tendency towards greater perplexed. He also noted that some systems, probability, takes millions of years, like life, seem to defy the classical second law because the bodies are so large and are of thermodynamics. However he recognized so far apart. The intermediate forms that living systems are open and not the assumed by solar energy, until it falls to adiabatic closed boxes of classical terrestrial temperatures, can be fairly thermodynamics. An organism stays alive in its improbable, so that we can easily use highly organized state by taking energy from the transition of heat from sun to earth outside itself, that is from a larger for the performance of work, like the encompassing system, and processing it to transition of water from the boiler to the produce a lower entropy state within itself. cooling instillation. The general Life can be viewed as a far-from-equilibrium struggle for existence of animate beings dissipative structure that maintains its local is therefore not a struggle for raw level of organization, at the expense of materials - these, for organisms, are air, producing entropy in the larger system it is part water and soil, all abundantly available of. - nor for energy which exists in plenty If we view the earth as an open in any body in the form of heat (albeit thermodynamic system with a large gradient unfortunately not transformable), but a impressed on it by the sun, the thermodynamic
by Eric Schneider and James Kay Life and the Second Law 15
imperative of the restated second law is that the system will strive to reduce this gradient by THE ORIGIN OF LIFE using all physical and chemical processes The origin of prebiotic life is the available to it. We have already shown that development of another route for the self-organizing processes are an effective dissipation of induced energy gradients. Life means of reducing gradients. We have with its requisite ability to reproduce, insures discussed that meteorological and that these dissipative pathways continue and it oceanographic circulation degrades some of the has evolved strategies to maintain these energy gradients and disequilibrium from the dissipative structures in the face of a fluctuating 1580 watts /meter2 of incoming solar energy. physical environment. We suggest that living However there are still additional energy systems are dynamic dissipative systems with gradients requiring dissipation. We suggest encoded memories, the gene with its DNA, that that life exists on earth as another means of allow the dissipative processes to continue dissipating the solar induced gradient and as without having to restart the dissipative process such is a manifestation of the restated via stochastic events. Living systems are second law. It is obvious that living systems sophisticated mini-tornados, with a memory are far from equilibrium dissipative systems (its DNA), whose Aristotelian "final cause" and have great potential of reducing radiation may be the second law of thermodynamics. gradients on earth (Ulanowicz and Hannon, However one should be clear not to overstate 1987). Much of this dissipation is the role of thermodynamics in living processes. accomplished by the plant kingdom (less than The restated second law is a necessary but not a 1% of it through photosynthesis, with most of sufficient condition for life. the dissipation occurring through evaporation This paradigm presents no contradiction and transpiration). with the neo-Darwinean hypothesis and the An interesting exception to this are the deep importance of the genetic process, and its role sea vent ecosystems that derive their energy in biological evolution. We reject the selfish from temperature and chemical gradients gene (Dawkins, 1976), as the only process in emanating from the sea floor rather than from selection and would insert the gene or species solar energy (Corliss, 1990). In these as a component in competing autocatalytic systems, life is most abundant where the ecosystems (Weber et al., 1989), competing to chemical and temperature gradients are the degrade available energy gradients. greatest, thus the required gradient dissipation The origin of life should not be seen as an is the highest. isolated event. Rather it represents the emergence of yet another class of processes whose goal is the dissipation of thermodynamic gradients. Life should be viewed as the most
by Eric Schneider and James Kay Life and the Second Law 16
sophisticated (until now) end in the continuum macromolecular species, Eigen has of development of natural dissipative structures proposed a simple phenomenological from physical to chemical to autocatalytic to rate equation materializing these three living systems. As we have discussed earlier necessary prerequisites. This rate autocatalytic chemical reactions are the equation, which we shall now call backbone of chemical dissipative systems. The Eigen's equation, is interpreted in terms work of Eigen (1971), Eigen and Schuster of the terminology of chemical (1979) connect autocatalytic and self- kinetics." reproductive macromolecular species with a Eigen (1971) himself says: thermodynamic vision of the origin of life. "Evolution appears to be an inevitable Ishida (1981) describes Eigen's work: event, given the presence of certain "Eigen (1971) has asserted that the first matter with specified autocatalytic steps of biological self-organization properties and under the maintenance of occurred in a structureless soup, the finite (free) energy flow necessary certainly involving functional to compensate for the steady production macromolecular structures such as of entropy" nucleic acids and proteins. In From the point of view of nonequilibrium accordance with this assertion he has thermodynamics of chemical reactions in a considered a chemical system homogeneous system, Eigen has shown that composed of a wide variety of self- the Darwinian selection of such reproductive macromolecules and many macromolecular species can be linked to different energy-rich monomers Glansdorff & Prigogine's stability criterion required to synthesize the (Nicolis and Prigogine, 1977 and Peacocke, macromolecules. Each macromolecular 1983). By examining the entropy changes and and monomeric species are distributed entropy production of such systems Ishida has uniformly throughout the available formulated a nonequilibrium thermodynamics volume. The system is open and of the hypercycles. This theory is used to maintained in a nonequilibrium state by discuss the stability of the "quasi-species" (a continuous flows of energy-rich and solution to Eigen's equations with non- energy-deficient monomers. It is thus vanishing mutation terms). In principle, it is tremendously complex. In addition, possible, using nonequilibrium metabolism, self-reproduction and thermodynamics of open systems, to put mutability are necessary for each forward scenarios for the development of macromolecular species to yield the biochemical machinery for the duplication and behavior of Darwinian selection at the translation of nucleic acids and other molecular level. For each macromolecules essential to life.
by Eric Schneider and James Kay Life and the Second Law 17
many species arrange themselves into leaf BIOLOGICAL GROWTH AND DEVELOPMENT index assemblies to optimize energy capture Our thesis is that growth, development, and and degradation. The gross energy budgets of evolution are the response to the terrestrial plants show that the vast majority of thermodynamic imperative of dissipating their energy use is for evapotranspiration, with gradients (Kay, 1984) and (Schneider, 1988). 200-500 grams of water transpired per gram of (Which is not to say this is the only imperative fixed photosynthetic material. This mechanism governing life, survival is equally important.) is a very effective energy degrading process Biological growth occurs when the system with 600 calories used per gram of water adds more of the same types of pathways for transpired (Kimmins, 1987). degrading imposed gradients. Biological Data synthesized by Currie and Paquin development occurs when new types of (1987) show that the large scale pathways for degrading imposed gradients biogeographical distribution of species richness emerge in the system. The larger the system, of trees is strongly correlated with realized i.e., the larger the system flow activity annual evapotranspiration and available energy. (Ulanowicz, 1986), the more reactions and The more energy is partitioned among species pathways (both in number and type) are the more pathways there are available for total available for gradient destruction. Clearly the energy degradation. Trophic levels and food above principle provides a criteria for chains are based upon photosynthetic fixed evaluating growth and development in living material and further dissipate these gradients by systems. All else being equal, the better making more higher ordered structures. Thus dissipative pathway is preferred. In what we would expect more species diversity to follows we explore some examples of this occur where there is more available energy. principle. Species diversity and trophic levels are vastly Plant growth is an attempt, within the greater at the equator, where 5/6 of the earths constraints of its genetic (and evolutionarily solar radiation occurs, and there is more of a tested) make up and its environmental gradient to reduce. boundary conditions, to capture solar energy and dissipate usable gradients. The gradient A THERMODYNAMIC ANALYSIS OF capturing aspects of plants can be seen in ECOSYSTEMS phototrophism and their symmetrical shapes, Ecosystems display the influence of designed to capture and degrade sunlight. thermodynamic principles in their patterns of Although each tree species has its own growth and development. A genetically endowed form, the energy capturing thermodynamically based theory of ecology aspect of an isolated tree leads to its holds the promise of propelling ecology from a magnificent symmetry. Canopies of plants of descriptive to a predictive science. Ecosystems
by Eric Schneider and James Kay Life and the Second Law 18
are the result of the biotic, physical, and within and through a system, the greater the chemical components of nature acting together potential for degradation. as a nonequilibrium dissipative process. As 3. More cycling of energy and material: such ecosystem development increases energy A) Numbers of cycles:- more pathways degradation thus following the imperative of for energy to be recycled in the system the second law. This hypothesis can be tested results in further degradation of the by observing the energetics of ecosystem incoming energy. development during the successional process or B) The length of cycles:- more mature by determining their behavior as they are systems will have cycles of greater stressed or as their boundary conditions are length, i.e. more nodes in the cycle. changed. Each chemical reaction at or within a As ecosystems develop or mature they node results in entropy production; the should increase their total dissipation, and more such reactions the more complete should develop more complex structures with the degradation. greater diversity and more hierarchical levels to C) The amount of material flowing in abet energy degradation. Species which cycles (as versus straight through survive in ecosystems are those that funnel flow) increases. The ecosystem energy into their own production and becomes less leaky thus maintaining a reproduction and contribute to autocatalytic supply of raw material for energy processes which increase the total dissipation degrading processes. of the ecosystem. In short, ecosystems D) Turnover time of cycles or cycling rate develop in a way which systematically decreases:- more nodes or cycles in a increases their ability to degrade the incoming system will result in nutrients or solar energy. energy being stored at nodes in the In this sense the development of ecosystem system resulting in longer residence maturity via succession is the result of the time in the system. This phenomena is system organizing itself to dissipate more the same as the decrease in incoming energy with each stage of succession. production/biomass (P/B) ratio Thus one would expect successional processes decreases observed in maturing in ecosystems to result in systems with: ecosystems. P/B is the residence time 1. More energy capture:- because the more of material in the system. The energy that flows into a system the greater residence time of a nitrogen atom in a the potential for degradation. simple bacterial cycle will be a matter 2. More energy flow activity within the of hours, however the residence time system:- again, the more energy that flows of a similar nitrogen atom in a rainforest will be years.
by Eric Schneider and James Kay Life and the Second Law 19
4. Higher average trophic structure: energy conductivity are all subsumed and A) Longer trophic food chains:- energy is explained by our theory. degraded at each step of the trophic If ecosystems develop into dynamic quasi- food chain, therefore longer chains stable states, one would expect them to respond will result in more degradation. to changes in boundary conditions that perturb B) Species will occupy higher average these states by retreating to configurations with trophic levels:- This will result in more lower energy degradation potential. Stressed energy degradation as energy at higher ecosystems will retreat down their trophic levels has a higher exergy thermodynamic branch into more primitive content. systems with attributes opposite those C) Greater trophic efficiencies:- energy that presented above (Kay, 1991). Stressed is passed higher up the food chain will ecosystems often appear similar to earlier be degraded further than energy that is successional stage ecosystems and will reside shunted immediately into the detrital at some distance closer to thermodynamic food chain. equilibrium. 5. Higher respiration and transpiration:- We have recently analyzed a carefully transpiration and respiration results in collected data set for carbon-energy flows in energy degradation. two aquatic tidal marsh ecosystems adjacent to 6. Larger ecosystem biomass:- more biomass a large power generating facility on the Crystal means more pathways for energy River in Florida. The ecosystems in question degradation. were a "stressed" and a "control" marsh. The 7. More types of organisms (higher stressed ecosystem is exposed to hot water diversity):- more types of organisms will effluent from the nuclear power station. The provide diverse and different pathways for stress is an approximately 6˚ C water degrading energy. temperature increase. The "control" ecosystem This list of ecological attributes can be is not exposed to the effluent but is otherwise explained by ecosystems behaving in such a exposed to the same environmental conditions. manner as to degrade as much of the incoming We wished to determine the effect of the energy as possible (Kay and Schneider, 1991, change in environmental conditions on the Kay, 1989) and provides causality for most if structure of the stressed system. not all the phenomenological attributes of Table 1 summarizes a set of ecosystem maturing ecosystems developed by Odum in indicators. The I/O or Input/Output Measures 1969. Lotka's (1922) suggestion that living indicate various aspects of the flows through systems will maximize their energy flow, H. the ecosystem. In absolute terms (the first T. Odum's (1955) maximum power principle three columns of Table 1) all the flows dropped for ecosystems and Lieth's (1976) maximum in the stressed ecosystem. Overall the drop in
by Eric Schneider and James Kay Life and the Second Law 20
TABLE 1: Ecosystem Indicators for the Crystal River Marsh Gut Ecosystems
Crystal River Mg/Sq m/day Scaled by Import Control Stressed ∆% Control Stressed ∆% Biomass 1,157,136 755,213 34.73% 157.50 125.49 20.32%
Total I/O Imports 7,347 6,018 18.09% 1 1 0.00% TST 22,768 18,055 20.70% 3.10 3.00 3.19% Production 3,292 2573.9 21.82% 0.45 0.43 4.56% Exports 952 872 8.37% 0.13 0.14 -11.86% Respiration 6,400 5,148 19.57% 0.87 0.86 1.80%
Living I/O Production 400 326 18.39% 0.05 0.05 0.37% Exports 316 253 19.93% 0.04 0.04 2.24% Respiration 3,566 3,078 13.69% 0.49 0.51 -5.37% To Detritus 5,726 4,315 24.64% 0.78 0.72 7.99%
Detritus I/O Scaled by Detritus Input Input from Living 5,726 4,315 24.64% 1.00 1.00 0.00% Production 2,893 2,248 22.29% 0.51 0.52 -3.11% Exports 636 619 2.64% 0.11 0.14 -29.19% Respiration 2,834 2,070 26.96% 0.49 0.48 3.09%
Food Web Cycles 142 69 51.41% Trophic Levels 5 5 0.00%
flows was about 20%, in particular the columns in Table 1) the resulting numbers imported flows (that is the resources available indicate how well the ecosystem is making use for consumption) drops by 18% and the TST of the resources it does capture. The (the total system throughput, the total flow percentage changes in these scaled flow rates activity in the system) dropped by 21%. The reveals that in total the stressed ecosystem is, biomass dropped by about 35%. The relatively speaking, exporting more. In other implication of these numbers is that the stress words, it is losing material more quickly than has resulted in the ecosystem shrinking in size, the control ecosystem. It is a leaky ecosystem. in terms of biomass, its consumption of Looking at the living side, the big changes are resources, and its ability to degrade and an increase in respiration and a decrease in flow dissipate incoming energy. to the detritus. There was a small decrease in If the flows are scaled by the import to the exports. These changes indicate that the ecosystem from the outside, (the last three consumed resources are being more effectively
by Eric Schneider and James Kay Life and the Second Law 21
used by the living components. It also analysis of these data and the implications of indicates the species are stressed. Looking at this hypothesis for ecosystem health or the detritus, a different picture emerges. There integrity are found in Kay and Schneider was a slight increase in production and a small (1991). decrease in respiration and a very large increase in exports. This analysis of the scaled flow ECOSYSTEMS AS ENERGY DEGRADERS rates indicates that the living components are The energetics of terrestrial ecosystems somewhat stressed but that more importantly, provides an excellent test of our thesis that there is a large break down in the ability of the ecosystems will develop so as to degrade ecosystem to recycle material through the energy gradients more effectively. More detritus and thus retain and degrade its developed dissipative structures will degrade resources. more energy. Thus we would expect more Examining the Food Web data further mature ecosystems to degrade the exergy confirms this. (The last three rows in Table 1.) content of the energy they capture more The number of cycles in the stressed ecosystem completely than a less developed ecosystem. is 51% of the number in the control. The exergy drop (i.e. gradient dissipation) Furthermore overall these cycles are shorter in across an ecosystem is a function of the length. In the effective grazing chain the difference in black body temperature between number of trophic levels was not changed, but the captured solar energy and the energy the trophic efficiencies were changed reradiated by the ecosystem. If a group of dramatically, as was the flow to the top trophic ecosystems are bathed by the same amount of levels. These are all indicators of a stressed incoming energy, we would expect that the ecosystem (Ulanowicz, 1985). most mature ecosystem would reradiate its Overall the impact of the effluent from the energy at the lowest exergy level, that is the power station has been to decrease the size of ecosystem would have the coldest black body the ecosystem and its consumption of resources temperature. (See equations next page.) The while impacting its ability to retain the black body temperature is determined by the resources it has captured. In short the impacted surface temperature of the ecosystem. ecosystem is smaller, has lower trophic levels, Luvall and Holbo (1989, 1991) and Luvall recycles less, and leaks nutrients and energy. et al. (1990) conducted experiments in which All of these are signs of disorganization and a they overflew terrestrial ecosystems and step backward in development. This analysis measured surface temperatures using a Thermal suggests that the function and structure of Infrared Multispectral Scanner (TIMS). Their ecosystems follows the development path technique allows assessments of energy predicted by the behavior of nonequilibrium budgets of terrestrial landscapes, integrating thermodynamic structures. A more complete attributes of the overflown ecosystems,
by Eric Schneider and James Kay Life and the Second Law 22
T ABLE 2. Radiative estimates from Thermal Infrared Multispectral Scanner for different ecosystem types in the H.J. Andrews Experimental Forest, Oregon. The data is presented from least (quarry) to most developed (400 year old forest). Data from Luvall and Holbo (1989).
Quarry Clearcut Douglas Natural 400 year old Fir Forest Douglas Fir Plantation Forest K* (watts/m2) 718 799 854 895 1005 L* (watts/m2) 273 281 124 124 95 2) Rn (watts/m 445 517 730 771 830 T (oC) 50.7 51.8 29.9 29.4 24.7 Rn/K* (%) 62 65 85 86 90
Rn/K*= percent of net incoming solar radiation degraded into nonradiative process.
including vegetation, leaf and canopy developed the ecosystem, the colder its surface morphology, biomass, species composition temperature and the more degraded it's and canopy water status. Luvall and his co- reradiated energy. workers have documented ecosystem energy Table 2 portrays TIMS data from a budgets, including tropical forests, mid-latitude coniferous forest in western Oregon, North varied ecosystems, and semiarid ecosystems. America. Ecosystem surface temperature Their data shows one unmistakable trend, that varies with ecosystem maturity and type. The when other variables are constant the more warmest temperatures were found at a clearcut
THE RADIATION EQUATIONS Rn = K*- L* where K* = Net flux of Solar Radiation (incoming), L* = Net Flux of long wave radiation (outgoing), Rn = Net radiation flux absorbed at surface (all measured in watts / meter2) and Rn = H + Le + G where H = sensible heat flux, Le = latent heat flux, G= energy flux into the ground. Rn is the energy which is degraded from radiation into molecular motion.
Furthermore: L*= ε [σ(T)4] where ε= emissivity, σ=Stefan-Boltzmann constant, T= surface temperature
IF K* IS CONSTANT, THE SMALLER T, THE SMALLER L* AND HENCE THE LARGER RN AND THUS THE LARGER THE AMOUNT OF ENERGY DEGRADED.
by Eric Schneider and James Kay Life and the Second Law 23
SURFACE TEMPERATURE (°C) VS TRANSECT DISTANCE (M)
40
38
36 BURN BURN 34 PASTURE 32
30
28 TREE ISLAND 26 50 100 150 200 250 300
FIGURE 3 A Thermal Infrared Multichannel Scanner (TIMS) profile over a varied landscape in the Braulio Carrillo National Park in Costa Rica (done by Luvall et al.1990). The TIMS is mounted on an aircraft measuring six thermal channels in the wave length channels of 8.2 to 12.2 µm and flown over a 400 meter transect. Temperatures are canopy temperature values calculated from net reradiated thermal energy. Temperatures showed that forest fire burn was the warmest system (it did not degrade as much incoming energy) and the tree island the coldest (the best degrader). The pasture degraded energy in an intermediate fashion. Airborne thermal imaging may hold great promise for rapid evaluation of terrestrial ecological integrity.
and over a rock quarry. The coldest site, points out that Rn is the net available energy 299°K, some 26° colder than the clear cut, was dissipated through evaporation, sensible heat a 400 year old mature Douglas Fir forest with a and storage. The ratio Rn/K* is the percentage three tiered plant canopy. The 23 year old of the radiative fluxes converted to lower naturally regrowing forest had the same exergy thermal heat. The quarry degraded 62% temperature as the 25 year old plantation of of the net incoming radiation while the 400 year Douglas Fir. Even with the initial planting of old forest degraded 90%. The remaining sites the late successional species of fir, the natural fell between these extremes, increasing system obtained a similar energy degrading degradation with more mature or less perturbed capacity in a similar time. ecosystems. Luvall's data allows for an interesting These unique data sets show that calculation of the percent of the net solar ecosystems develop structure and function that radiation (K*) that is degraded into energy in degrades imposed energy gradients more the form of molecular motion (Rn). Luvall effectively. Analysis of airborne collected
by Eric Schneider and James Kay Life and the Second Law 24
SURFACE TEMPERATURE (°C) VS TRANSECT DISTANCE (M)
60
50
40
30 c a b d e g k l m f hij 20
10 0 200 400 600 800 1000 FIGURE 4: Temperature profiles along a 1 km transect in the H.J. Andrews Experimental Forest, Oregon. (Luvall & Holbo, 1991) The top profile is for noon and the bottom profile is for post-sunset. The data was collected using TIMS surface temperature acquisition system. The letters on the diagram correspond to surface features: a) edge of forest, b) narrow road, c) somewhere in a clear cut, d) a wider road, e) one side of a small shelter wood of Douglas Fir, f) a pond within the shelter wood, g) the other side of the shelter wood, h) a wide road, i) trees along the road, j) in a flat part of a clear cut, k) somewhere in a 15 year old Douglas Fir plantation, l) a trail, m) an old stand of Douglas Fir regrowth.
reradiated energy fluxes appears to be a unique ecosystems, as well as method development to and valuable tool in measuring the energy correct for system specific location dependant budget and energy transformations in terrestrial energy processes, i.e. rainfall and altitude. The ecosystems. According to proposals made in potential for these methods to be used for this paper, a more developed ecosystem remote sensed ecosystem classification and degrades more energy. Thus the ecosystem ecosystem health evaluation is apparent in temperature or Rn/K* may be excellent Figure 3 & 4. Forest fire burn, pasture and indicators of ecological integrity that can be trees have their own distinctive temperatures. formulated from first principles of More mature ecosystems are colder. Luvall has thermodynamics and physics. also tested algorithms to measure the thermal For these indices to be used to determine inertia of ecosystems, analyzed spectral comparative or, hopefully, absolute measures variability, day night differences and of ecosystem integrity, much more research is evapotranspiration, all which show specific needed on energy transformation in ecosystem characteristics.
by Eric Schneider and James Kay Life and the Second Law 25
Energy absorbed Energy Reradiated Sensible Heat Evapo- AREA at surface Long Wave Flux transpiratrion Amazon 184.7 17% 15% 70% US 220.2 18% 19% 61% Asia 223.4 24% 26% 50% Sahara 202 41% 56% 2%
Rain Forest 204 16% 22% 63% Grassland 186 22% 30% 48%
TABLE 3 Energy absorbed (watts/ m2/ day) at the surface of varied ecosystems, and the percentage of this energy which is emitted into space . Data was obtained from the satellite derived Earth Radiation Budget Experiment and from the SiB climate biosphere model of Sellers et al. (1986). This data demonstrates that a more developed ecosystem is a better dissipative structure.
These same phenomena are observed at a processes which influence radiation, larger scale and exhibit the global nature of the momentum, mass, and heat transfer related to biosphere in reducing the induced solar vegetation-surface atmosphere interactions. gradient on earth. Sato and his colleagues have Their calculations are important because they recently calculated the mean surface energy integrate the atmosphere-biosphere as a net budget for four large regions of the earth for 50 dissipative system and allow for the days in the summer. (See Table 3) The regions determination of the reduction of the solar are a) the Amazon basin which is uniformly induced gradient between a warm black body covered by rainforest, b) central and eastern earth and the 2.8°K temperature of outer space. United States which consists mainly of The first four rows presented in Table 3 are cultivated land, grasslands and some mixed arranged from the most developed ecosystem forest, c) Asia, a heterogeneous mix of tropical (Amazon rainforest) to the least. The re- rain forest, forest, cultivated land and desert, radiated long wave radiation and the sensible and d) the Sahara desert. Their data was heat flux represent energy which has not been obtained from the satellite derived Earth degraded to the ambient and which will cause Radiation Budget Experiment and from the SiB disequilibrium. Evapotranspiration represents climate biosphere model of Sellers et al. energy which is dissipated and thus been (1986). They measured insolation, albedo, net converted to lower quality exergy. On the long and short wave energy absorbed at the basis of the arguments presented in this paper, earth's surface, net radiation or available evapotranspiration should increase with energy and calculated important heat fluxes by ecosystem development and long wave modeling physiological and biological radiation and sensible heat flux should
by Eric Schneider and James Kay Life and the Second Law 26
FIGURE 5. The mean monthly outgoing long wave radiation (OLR) is measured by the NOAA-9 polar orbiting satellite using the infrared channel. Contours are in watts/m2. Note the low longwave emissions over the tropical rain forests and high values over the earth's deserts.
decrease. This is borne out by the results Java, L is less than 200 watts/m2. The deserts presented in the first four rows of Table 3. emit a net OLR of over 280 watt/m2. Moreover the last two rows represent Interestingly enough, the tropical rain forests running the SiB model for the rainforest and with their coupled cloud system, with the sun then for the same location except assuming a directly overhead, have the same surface grassland instead of a rainforest. (Shulka et temperature as Canada in the winter. The low al., 1989). Again, this data shows that the tropical rainforest OLR temperatures are due to more developed an ecosystem, the more the the cold temperatures of the convective cloud energy impinging on it is degraded to lower tops which are generated by the underlying quality energy. cooler forests. Satellite derived earth radiation data As we have seen earlier, mature ecosystems developed for global climate analysis, shows can lower surface temperature by that this same phenomena may also be apparent approximately 25°C. The low reradiation from at the global scale. The Climate Analysis the rainforest-cloud systems appears to be a Center and the Satellite Research Laboratory of global scale signal of solar gradient the National Oceanic and Atmospheric degradation. Most of the energy degradation in Administration (NOAA) produce monthly maps terrestrial ecosystems is due to the latent heat of outgoing longwave radiation (OLR) production via evapotranspiration. Tropical collected from multiwave spectral scanners rain forests produce a prodigious amount of aboard polar orbiting satellites. water vapor via this process, and convective Long wave infrared emissions (L) from the induced cooling produces high clouds which earth are dependant on the surface temperature, tends to reinforce the cooling of the rain greenhouse gasses, i.e. H20 and CO2, and forests. The coupled rain forest cloud system cloud cover. Like the greenhouse gasses, lowers the earth to space gradient even more cloud cover will tend to act as a blanket and than the forest alone. trap longwave infrared. This phenomena may appeal to supporters Figure 5 is a global OLR map for February of Lovelock's (1990) Gaia hypothesis, as it is 1991. For the tropical rainforests of the an example of the coupled global biosphere- Amazon, the Congo, and over Indonesia and climate system. Without immersing ourselves
by Eric Schneider and James Kay Life and the Second Law 27
into the Gaiaean controversy, the coupled described how they apply to mesoscale system does decrease the apparent earth-space meteorology. We apply these same principles gradient. Furthermore the rain forests with to the origin of life, biological growth, the their attendant cloud formation act to cool the development of ecosystems, and biological earth on a global basis and thus play an evolution. Living systems are not only important role in global climate energy budgets. permissible under the restated second law of We have research underway to further quantify thermodynamics, but it is the restated second these propositions. law which mandates living processes and is a necessary but not sufficient cause for life itself. DISCUSSION We provide biology with a paradigm that not In this paper we have recast the second law only describes the "why" of life but also of thermodynamics from the old statement of describes the directions in which living systems "entropy increase" into a statement that will develop and evolve. describes systems undergoing processes so that We have documented that ecological they will reach a unique state of equilibrium. processes are driven and governed by This description draws on the work of thermodynamic imperatives; ecosystems Carathéodory, Hatsopoulos & Keenan, and develop and select energetic pathways that Kestin. It allows for the discussion of system strive to degrade as much of the energy behaviour in nonequilibrium situations. It available to them as possible. We believe that overcomes the difficulty of describing these same principles extend to Darwinean nonequilibrium systems in terms of entropy, selection. Margalef (1968), Odum (1969), which can only be defined in the equilibrium Wicken (1987) and Schneider (1988) all state. We suggest that, in nonequilibrium observed that the strategy of succession, a situations, systems will take advantage of all short term process, is basically the same available means to resist the gradients strategy as the long term evolutionary responsible for the nonequilibrium condition. development of the biosphere. Margalef Furthermore, the stronger the applied gradient, (1968) noted that: the greater the effect that the equilibrium "evolution cannot be understood except attractor will have on the system. Emergence in the framework of succession. By the of coherent self-organizing structures are the natural process of succession, which is expected response of systems as they attempt to inherent in every ecosystem, the resist and dissipate the external gradients that evolution of species is pushed or are moving them away from equilibrium. sucked onto the direction taken by We have shown that these principles are succession. Succession is in progress manifested in the behaviour of physical everywhere and evolution follows dissipative systems (i.e. Bénard cells) and encased in succession's frame.".
by Eric Schneider and James Kay Life and the Second Law 28
Zotin (1984) studied the bioenergetic trends of development and evolution represent the the evolution of organisms and noted that development of new dissipative pathways. evolution has progressed in a manner such that This work is quite different than Jørgensen's organisms evolved with increasing energetic Maximum Exergy Principle (Jørgensen and dissipation rates, i.e. respiratory intensity. Mejr,1979). He has focused on exergy Evolution, like ecosystems seems to select concentrations, while we are investigating species and ecosystems that increase the global exergy degradation. The two concepts may be dissipation rate. interrelated but our work has not as yet shown Our suggestions should not be confused the linkage. with the work of Brooks and Wiley (1986). Our proposals represent a new approach to Their "increase of entropy", observed in their the biological synthesis. We have not been cladograms of evolving species, refers to an able to discuss all the ramifications these information theoretic entropy and as such principles have for our understanding of the explains things in terms of microstate growth and development of biological systems. probabilities of information states. Our work We have intentionally not discussed the examines the thermodynamic development of application of these principles to the natural systems and as such explains things in development and operation of genetic terms of macroscopic behaviour of energy processes. We note that our thermodynamic processing. description of living systems fits comfortably The foundations of our work were certainly into the present day molecular-genetic research developed by Prigogine and Wiame (1946) and program. The importance of the gene and its Wicken (1980, 1987) but we circumvent their role in morphogenesis, speciation and in discussions of entropy and life, and instead carrying the message of evolution forward is rely on a more appropriate approach to vital. nonequilibrium systems, that is the Life represents a balance between the development of self-organization as a means of imperatives of survival and energy degradation. dissipating gradients imposed on systems. To quote Blum (1968): Lotka (1922) and Odum and Pinkerton "I like to compare evolution to the (1955) have suggested that those biological weaving of a great tapestry. The strong systems that survive are those that develop the unyielding warp of this tapestry is most power inflow and use it to best meet their formed by the essential nature of needs for survival. Our work would propose elementary non-living matter, and the that a better description of these "power laws" way in which this matter has been would be that biological systems develop in a brought together in the evolution of our manner as to increase their degradation rate, planet. In building this warp the and that biological growth, ecosystem second law of thermodynamics has
by Eric Schneider and James Kay Life and the Second Law 29
played a predominant role. The multi- thus providing a unifying macroscopic theory colored woof which forms the detail of for living systems. the tapestry I like to think of as having been woven onto the warp principally ACKNOWLEDGEMENTS: by mutation and natural selection. The authors wish to thank Prof. Pete While the warp establishes the Silveston, Prof. T.E. Unny, and Prof. T. dimensions and supports the whole, it Hollands, University of Waterloo, and Prof. is the woof that most intrigues the W. Brown, University of New Hampshire for aesthetic sense of the student of organic data and help with the Bénard cell analysis, and evolution, showing as it does the Dr. P. Sellers of the University of Maryland beauty and variety of fitness of for help with SiB data. Dr. Jeffrey Luvall of organisms to their environment. But NASA provided us with his airborne why should we pay so little attention to multispectral scanner data and Dr. Arnold the warp, which is after all a basic part Gruber of NOAA provided us with OLR of the whole structure? Perhaps the satellite data. Prof. R.E. Ulanowicz of analogy would be more complete if University of Maryland shared his data sets, something were introduced that is software, and many hours of his time. occasionally seen in textiles-the active Professor Donald Mikulecky of Virginia participation of the warp in the pattern Commonwealth University has served as an itself. Only then, I think, does one excellent consultant on thermodynamic issues. grasp the full significance of the Finally we thank R. Swenson and H. analogy." Morowitz for disagreeing with us and What we have tried to do in this paper is to motivating us to investigate further. show the participation of the warp in producing BIBLIOGRAPHY the pattern of the tapestry of life. However this Ahern, J.E. (1980) The Exergy Method of Energy does not in anyway diminish the importance of Systems Analysis.: J. Wiley and Sons.
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by Eric Schneider and James Kay