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K-T Transition into Chaos

Dewey M. McLean

Abstract

Earth has a hot interior, and is surrounded by a celestial heat sink. The energy outflow forced by the thermal gradient determines the direction and rate of evolution of the Earth. Negative feedbacks in the Earth maintain steady state heat loss, and long-term steady state mantle CO2 degassing onto Earth's surface to which surficial feedback systems become organized; spasmodic degassing events destabilize feedback systems, triggering disorganization.

Earth's surface is intermediate between a solar energy source and a celestial sink. Energy flow from the sun to Earth to space (S-E-S) maintains the biosphere as a far-from-equilibrium system, organizing it as a function of flow rates. Greenhouse gases (dominantly H2O and CO2) influence the flow rate; degassing, and cycling through feedback systems, control composition of the atmosphere, and thus the S-E-S energy flow.

Far-from-equilibrium systems contain fluctuating subsystems; fluctuations can grow into structure-breaking waves that invade a system, shattering organization, and causing it to disintegrate into chaos. During the K-T, 65 Ma ago, spasmodic volcanic injection of CO2 into surficial feedback systems that were organized to steady state degassing triggered massive disorganization. The Deccan Traps volcanism, possibly the greatest volume of continental basalts on Earth's surface, destabilized surficial feedback systems and S-E-S energy flow, shattering Late Cretaceous organization of the biosphere, and triggering a K-T transition into chaos.

Introduction

To discover cause of the Cretaceous-Tertiary transition (K-T) extinctions of 65 Ma ago requires understanding of the K-T as a function of evolving feedback systems within the context of thermal evolution of the Earth. System dynamics, which permits handling of large amounts of multidisciplinary data, provides the methodology. In this paper, which I have been working on for over a decade, I use system methodology to explore how self-regulated heat flow from Earth's interior to outer space controls mantle CO2 degassing. The latter, by affecting surficial feedback systems, and regulating the concentration of greenhouse gases in the atmosphere that influences the Sun-Earth-Space (S-E-S) energy flow (Figure 1), maintain the biosphere as a far-from-equilibrium system.

Long term stability of mantle CO2 degassing permits surficial feedback systems to become organized to the degassing flux rate, producing global ecological stability to which the biosphere becomes organized. However, during times of intensive mantle plume volcanism CO2, the greatly increased CO2 flux destabilizes surficial feedback systems which, in conjunction with destabilized S-E-S flow, triggers general disorganization of the biosphere. Volcanism occurring as start/stop pulses is particularly destabilizing because as feedback systems are in the process of organizing to a given flow rate, they are hit by another. Breakdown of stabilizing negative feedback systems, and their replacement by runaway growth/collapse positive feedback systems, exacerbates instability and disorganization.

Far-from-equilibrium systems that are in steady state contain subsystems that are continually fluctuating; small perturbations or fluctuations, as a result of positive feedback, may become amplified into gigantic, structure-breaking waves that invade the entire system, shattering preexisting organization, and causing a system to disintegrate into chaos (Prigogine and Stengers, 1984). During the K-T, 65 Ma ago, the Deccan Traps mantle plume volcanism in India, possibly the greatest volume of continental basalts on Earth's surface (Subbarao & Sukheswala, 1981), occurred as start/stop pulses in which basalt flows are separated by intertrappeans (sediments). In effect, the Deccan Traps volcanism was a thermodynamical fluctuation that, by destabilizing surficial feedback systems and S-E-S energy flow, became amplified and shattered preexisting organization of the biosphere, triggering a K-T transition into chaos.

Background

A decade ago (McLean, 1978), I proposed perturbation of the carbon cycle as a factor in the trans-K-T global extinctions, citing failure of the dominant Cretaceous marine planktonic algae, the coccolithophorids, as trigger of the perturbation. Via production of CaCO3 shells and organic tissue that settle into the deep oceans by gravity, those algae "pump" CO2 from the marine mixed layer and the atmosphere into the deep oceans maintaining relatively low mixed layer and atmospheric pCO2. Failure of the modern pump would elevate atmospheric pCO2 severalfold (Energy and Climate, 1977); thus, the K-T failure of the coccolithophorids would have produced a K-T perturbation of the carbon cycle. Noteworthy is the fact that the carbon isotope record showed direct evidences of a major K-T perturbation.

In 1978, I could not account for cause of the coccolithophorid extinctions; however, a potential key to the K-T existed in the carbon isotope record which indicated a major K-T drop in carbon-13 (C-13) values. Mantle CO2 is depleted in C-13 and it seemed reasonable that a major release of mantle CO2 might account for the C-13 shift. Literature search disclosed that the Deccan Traps volcanism in India had begun erupting at about the time of the marine K-T boundary (Wellman and McElhinny, 1970); its estimated duration from 65-60 Ma coincided with the perturbation of the C-13 record. At the Toronto AAAS meeting (McLean, 1981a), and the Ottawa K-Tec II (McLean, 1981b), I proposed the Deccan Traps as the initiator of the K-T carbon cycle perturbation. The combination of Deccan Traps and coccolithophorid failure triggered a major K-T perturbation of the carbon cycle, and the global K-T extinctions. I later proposed the K-T as but a special case within a general scenario of mantle degassing (McLean, 1985a, b, c).

Recently (McLean, 1987 a, b), I subsumed previous work into Earth's thermal evolution, proposing that self-regulated heat flow from Earth's interior to the space heat sink surrounding Earth (after Tozer, 1972) maintains a general steady state mantle CO2 degassing to which the biosphere becomes organized, but that mantle plume volcanic activity, by adding to the steady state CO2 flux, can trigger disorganization of the biosphere.

This current paper integrates mantle degassing with feedback systems, and the Sun-Earth-Space (S-E-S) energy flow system, the primary source of energy that drives Earth's biosphere.

Solar-Earth-Space Energy Flow Ssystem

The biosphere is an open system freely exchanging energy and matter with the environment. Whereas equilibrium systems require either isolation (adiabatic systems), or contact with a single fixed reservoir (isothermal systems), open systems are in contact with more than one reservoir, some of which are sources and some sinks (Morowitz, 1979). Earth's surface is a system intermediate between a solar energy source and a celestial sink (Figure 1). Flow of energy from the sun to Earth and on to space (S-E-S) maintains the biosphere as a nonequilibrium system, organizing it as a function of flow rates. The S-E-S energy flow maintains the biosphere as a nonequilibrium system; cessation of the flow would cause the biosphere to move toward equilibrium. Approximate steady state exists between the flux of solar radiation and the loss of energy to outer space. Steady state energy flow maintains a system maximally far from equilibrium (Morowitz, 1979), a necessity for maintaining long-term stability of the biosphere.

Greenhouse gases in the atmosphere, dominantly H2O and CO2, influence the S-E-S flow rate. These gases are transparent to short-wavelength radiation from the sun which warms Earth's surface; Earth then radiates this heat energy as long-wavelength infrared radiation. However, greenhouse gases are opaque to infrared radiation, and absorb it, causing the atmosphere to warm up; the long-wave radiation that is returned to the surface is the "greenhouse" effect. The long-wave radiation returned to the surface is equivalent to about 92 percent of the average solar energy incident on the atmosphere (Kuhn, 1985). Of course, some escapes to space, maintaining more or less steady state flow from source to sink. Of the dominant greenhouse gases, H2O and CO2, the former accounts for about two thirds of the greenhouse effect. Together, they raise Earth's surface temperature about 30o K to 288o K (Levine, 1986). That solar energy is the dominant energy flux controlling organization the biosphere is shown in Figure 2 (after Miller and Urey, 1959).

The biosphere originated in near equilibrium conditions with low order (a measure of how far a system is from equilibrium) and high probability; evolution has been toward higher order, and lower probability (Konoplev et al., 1978; Zotin and Konoplev, 1978). Continued evolution is dependent upon flux of solar energy as an organizing, or ordering, factor. Why this flux is an organizing factor is next discussed.

Energy flow from a source into an intermediate system requires that the source must be at a higher kinetic temperature. The flux causes upper lying energy levels in the intermediate system to become populated; they then take a finite time to decay into thermal modes. During this time, energy is stored in the upper states such that the system is at a higher Helmholtz free energy than it would be at equilibrium, producing an ordered configuration. In intermediate systems, stable covalent, ionic, or metallic bonds store large amounts of energy. Such long lived bonds achieve a high order measure (Morowitz, 1979).

Steady state S-E-S energy flow is necessary for long-term global ecological stability. However, S-E-S flow can vary as a function of Earth mantle degassing, triggering ecological instability. Such instability is recorded in the geological record as the K-T extinctions.

Mantle Degassing as a Function of Thermal Evolution of the Earth

Earth is believed to have accreted within a primordial cloud of hydrogen, helium, metallic oxides, silicates, aluminates, titanates, and ices of methane, ammonia, water, and CO2, via accretion of planetesimals and other debris. Volatiles trapped within the proto-Earth continue to be degassed from the interior via volcanoes, fumaroles, and hot springs. Excellent discussions of Earth's origin, and internal structure and processes, may be found in The Interior of the Earth: Its Structure, Constitution and Evolution (Bott, 1982), Mantle Flow and Plate Theory (Garfunkel, 1985), The Earth's Core (Jacobs, 1987), and Energetics of the Earth (Verhoogen, 1980).

Two categories of models address accretion of the proto-Earth: non-homogeneous and homogeneous accretion models. By the former, initial accretion of iron particles formed an iron-rich core about which the mantle later accreted (Bott, 1982). By the latter, accretion produced an initially homogeneous proto-Earth. Later melting of iron-nickle parti-cles and draining of the dense liquid phase to Earth's center formed the iron-nickle core, displacing lighter weight elements outward to form the mantle, crust, hydrosphere, and, in part, the atmosphere.

Whatever the mechanism of core formation, Earth has a hot core and is surrounded by a cold celestial heat sink. The energy outflow forced by this thermal gradient is probably the principal factor determining the direction and rate of evolution of the Earth (Maj, 1984). This thermodynamical heat engine drives mantle convection, and thus plate tectonics and mantle degassing.

Earth has evolved through four thermal stages (after Bott, 1982): (1) initial heating by impacts, gravitational compression, and decay of short-lived radioactive isotopes, lasting less than 1 Ma, (2) heating via release of gravitational energy during core formation from an homogeneous Earth, and start of vigorous convection in core and mantle, lasting 1-100 Ma, (3) thermal equilibrium between heat production by long-lived radioactive isotopes, steady cooling, and heat loss from the surface, lasting a few hundred Ma, and (4) stable thermal balance between heat production, and slow steady heat loss, starting 4 billion years ago, and persisting to today. This self-regulating aspect of Earth's thermal evolution comes from the work of Tozer (1972) and is important to the evolution of Earth's biosphere.

Tozer (1972) indicates that a planet with heat sources will heat up until convection is established. Thereafter, mantle temperature and viscosity function together to establish a balance between internal heat production and loss. By this self-regulating mechanism, local increases in heat production will lower viscosity, enhancing convection that carries away the excess heat. Conversely, local decreases in heat production will increase viscosity, slowing down convective removal of heat and allowing the temperature to rise to near its previous value. By means of this temperature-viscosity relationship, a convecting planet will settle down into a quasi-equilibrium temperature distribution, and a balance between heat production and loss. Verhoogen (1980) also argues for steady state between internal heat/entropy production and heat loss. Steady state heat loss implies steady state convection, and thus steady state mantle CO2 degassing that would be conducive to global ecological stability over geologically long time intervals.

Earth loses most of its heat, about 75 percent, through the ocean basins. The general mantle convective pattern, after Turcotte and Oxburgh (1967) and Oxburgh and Turcotte (1968), shows lower mantle material heated at the mantle/core interface and then rising as hot plumes to form new litho-sphere beneath ocean ridge crests. Heat is lost as the new oceanic litho-sphere spreads laterally away from the ocean ridges. The chilled lithosphere descends as plumes at subduction zones. The mantle is assumed to behave as a Newtonian viscous fluid in which free thermal convection may occur when heated from below, and has an inferred Rayleigh number of 105 to 106 (Bott, 1982).

A subordinate mechanism whereby the remaining 25 percent of internal heat escapes through the continental lithosphere is by mantle plume, "hot spot," volcanism (e. g., Wilson, 1963; Morgan, 1971, 1972; Crough, 1979; Loper and Stacey, 1983; Loper, 1985). Contrasting with the steady loss by upwelling at ocean ridges, hot spot volcanism involves spasmodic escape of heat from the deep mantle. It may function as safety valves for heat es-cape from Earth's deep interior where new oceanic lithosphere is not formed. Hot spot sources differ from the reservoir that supplies material to the mid-oceanic ridges (Garfunkel, 1985). The relation of some hot spots to continental breakup and formation of new oceanic ridges suggest that mantle diapirs interfere with, and modify the large scale flow. Mantle plume activity in the form of the Deccan Traps continental flood basalt volcanism drove mantle CO2 flux rates above the steady state to which pre-K-T surficial feedback systems were organized.

S-E-S Energy Flow Ccoupling

The causal-loop diagram of Figure 3 shows important feedbacks operating during times of steady state mantle CO2 degassing. Causal-loop diagrams are excellent for illuminating generalities of system behavior, and are the basis for developing flow diagrams, and system equations, to rigorously examine systems behavior. Excellent introductions to system dynamics may be found in Principles of systems (Forrester, 1968), Study Notes in System Dynamics (Goodman, 1974), and Introduction to Computer Simulation (Roberts et al., 1983).

In developing a causal diagram, identification of key variables is the first step. Cause-effect, or causal, relationships between pairs of variable are established (Figure 4, upper part) by connecting pairs with an arrow which symbolizes "causes," "influences," or "affects." Thus, independent variables are at the tail of the arrow, and dependent variables at the head. The arrows express asymmetrical, and irreversible, relationships.

Correlation between variables of a pair is next determined. In cases where an increase in the independent variable produces increase in the dependent variable, the variable are positively correlated, and a plus sign is placed next to the arrowhead (Figure 4). Conversely, if an increase in the independent variable causes decrease in the dependent variable, the correlation is negative, and a minus sign is placed next to the arrowhead.

Finally, causal pairs are linked to other pairs (Figure 4, lower part). Closure indicates a feedback loop. Polarity of the loop is determined by counting the number of minus signs in the loop; an even number indicates positive polarity, and odd number, negative polarity. The polarity is enclosed with a curved arrow that indicates the direction of flow of energy/material through the loop and is displayed within the loop. Positive feedback produces runaway growth/collapse, and negative feedback system stability.

Negative feedback behavior is synonymous with teleological behavior (Rosenblueth et al., 1968). In application to Earth's thermal evolution, Earth ex-hibits goal-seeking, or teleological, behavior on two levels: (1) as a part of the universe, Earth is evolving toward the thermodynamical equilibrium "entropy death" of the universe, and (2) self-regulating behavior controlling heat flow from Earth's hot core to the space heat sink is via negative feedback. Ashby (1968) notes that "We have heard ad nauseam the dictum that a machine cannot select; the truth is just the opposite: every machine, as it goes to equilib-rium, per-forms the corresponding act of selection." Teleological behavior originating in the interior of the Earth controls the actions of numerous feedback systems that, all operating together, guide evolution of the biosphere.

Feedback Systems Coupling to the Biosphere: General Discussion

Figure 3 represents times of steady state mantle CO2 degassing to which surficial feedback systems become organized. Stability of mantle CO2 flux permits stability of energy/matter flow through interactive self-organizing surficial feedback systems that further enhances global ecological stability. Earth's hot core (lower right corner) drives convection that transports mantle CO2 onto Earth's surface. Negative temperature-viscosity-convection feedback loops at Earth's core-mantle interface maintain steady state between heat production and loss, and thus general steady state mantle CO2 degassing.

However, during times of intensive mantle plume volcanism CO2, the greatly increased CO2 flux destabilizes surficial feedback systems which, in conjunction with destabilized S-E-S flow, triggers general disorganization of the biosphere. Volcanism occurring as start/stop pulses is especially destabilizing; as systems are becoming organized to new flow rates, they are hit by new ones, and are thus in constant states of overshoot and collapse. Breakdown of stabilizing negative feedback systems, and their replacement by runaway growth/collapse positive feedback systems, exacerbates instability and disorganization. Mantle plume volcanism occurring in start/stop pulses, is especially disruptive. Massive breakdown of negative, stabilizing, feedback systems, and their replacement by positive runaway growth/collapse feedback would trigger transition from order to chaos which, if severe enough, could cause global scale extinctions, as during the K-T

During the K-T, the Deccan Traps mantle plume volcanism in India, cited as possibly the greatest volume of continental basalts on Earth's surface by Subbarao & Sukheswala (1981), occurred as start/stop pulses of trappean eruptions separated by quiescence; the latter are indicated by intertrappeans (sediments). The Deccan Traps volcanism, by destabilizing both surficial feedback systems and the S-E-S energy flow, would have triggered massive disorganization of the biosphere.

Systems Instability in the K-T Global Extinctions

Prior to the K-T extinctions, global ecological stability had prevailed (Thierstein, 1981). It was punctuated by global ecological instability for at least 0.5 to 1 Ma--for the duration of the Deccan Traps volcanism. Global ecological stability returned during the Early Tertiary.

The Deccan Traps volcanism was perhaps a unique Phanerozoic event. Subbarao and Sukheswala (1981) state that it is possibly the greatest volume of continental basalts on Earth's surface. Alexander (1981) says that of the major episodes of flood basalt volcanism the Deccan Traps has, by far, the greatest volume of all and was erupted over the shortest time span. Courtillot and Cisowski (1987) call the Deccan Traps the largest volcanic event in the last 200 Ma. Original lava coverage is estimated at 2.6 x 106 km2 (Pascoe, 1964); today, after extensive erosion, it yet covers 5 x 105 km2 of western and central India from a thickness of 2000 m near Bombay to 100-200 m in central India (Bose, 1972). The bulk of this enormous volume may have been erupted in only 0.5 Ma (McLean, 1985 a, b, c; Courtillot and Cisowski, 1987).

An estimate of mantle CO2 release by the Deccan Traps can be made by comparing its basalt production with that of modern mid-ocean ridge basalt (MORB) production. Based on a modern total ridge length of 6 x 104 km, basalt thickness of about 1 km, and a spreading rate of 1 cm/yr, modern MORB production is about 1.2 km3/yr. Using Pascoe's estimate of original coverage (at 1 km average thickness), and a duration of 0.5 Ma, Deccan Traps basalt production would have been 4.91 km3/yr, a rate 4 times that of modern MORB production. Courtillot and Cisowski (1987) estimate average extrusion rates at about 2 km3/yr. Whichever, the Deccan Traps addition to MORB production was significant. Estimate of the Deccan Traps CO2 release can be made by comparing it with a rough guess at pre-K-T steady state mantle degassing.

Modern CO2 degassing from all sources (after Leavitt, 1982) is 4.1 x 1012 moles CO2/yr. Using Leavitt's estimate as a basis for pre-K-T degassing values, duration of 0.5 Ma, and Pascoe's estimate of original volume, the Deccan Traps CO2 flux superimposed upon steady state flux would have enhanced the total annual mantle CO2 flux by about 25 percent (a figure that, based on uncertainties of a world 65 Ma distant is, at best, a wild guess).

Whatever the CO2 flux rate of the Deccan Traps volcanism, the world was set up perfectly for maximum effects of a major degassing event. In times of vigorous oceanic circulation and cold deep oceans, the deep oceans take up and store CO2. However, during the K-T marine circulation was sluggish, and the deep oceans were warm (14o-15o C), reducing capacity of the deep ocean CO2 sink to rapidly take up CO2 which would have tended to accumulate in the atmosphere and marine mixed layer. That, plus the failure of the coccolithophorids, would have caused a major degassing event to have maximum impact upon surficial feedback systems.

A Transition into Chaos

Deeper understanding of the implications of the Deccan Traps as a thermodynamical event as a part of Earth history emerges from the work of Prigogine and Stengers (1984). In far-from-equilibrium conditions, systems contain subsystems that are continually fluctuating. However, a single fluctuation or a combination of them may become so powerful as a result of positive feedback, as to become amplified and invade the entire system. Very small perturbations or fluctuations can become amplified into gigantic, structure-breaking waves, shattering preexisting organization, and causing a system to disintegrate into chaos. Viewed in this light, the Deccan Traps volcanism was a thermodynamical fluctuation that, by destabilizing surficial feedback systems, became amplified, and shattered organization of the biosphere, triggering a K-T transition into chaos.

During the K-T, pulses of start/stop Deccan Traps mantle plume volcanism would have destabilized energy/matter flow in virtually all aspects of surficial feedback systems: atmospheric and marine mixed layer pCO2, soil chemistry, photosynthetic rates, microbial activity, climatology, to name a few. Such was the destabilization that Deccan Traps-induced disorganization of the biosphere defines the boundary between the Mesozoic and Cenozoic Eras (McLean, 1982).
Leisurely changes in mantle CO2 injection into surficial feedback systems allow time for them to organize to new energy/matter flow rates. However, rapid start/stop pulses of CO2 injection would be destabilizing and disorganizing. It can hardly be otherwise. While feedback systems are in the process of organizing to a new flow rate, they are hit with others, causing them to continually overshoot and collapse in response to changing environmental conditions. Instabilities that would loop upon themselves in positive runaway growth/collapse exacerbate further instabilities. One such rickety ecosystem, that in normal times helps to maintain low atmospheric and mixed layer pCO2, but whose collapse can trigger CO2 accumulation in the atmosphere/mixed layer, is the Williams-Riley pump in the oceans.

Marine algae utilize CO2 in the photosynthetic process, locking it up into organic particulates. The coccolithophorids also produce platelets of CaCO3; these particulates settle by gravity into the deep oceans, in effect, "pumping" CO2 from the surficial environments into the deep oceans where it is stored in the sediments. This, the so-called Williams-Riley pump, maintains relatively low mixed layer and atmospheric pCO2. The National Research Council indicates that modern failure of the pump would raise atmospheric CO2 levels severalfold (Energy and Climate, 1977).

The K-T failure of the coccolithophorids, whose CaCO3 particulates produced the great Cretaceous chalk deposits, could have only disrupted the Williams-Riley pump of CO2 from the atmosphere/mixed layer into the deep oceans; CO2 that the coccolithophorids previously locked up in marine sediments would have been released into other feedback systems causing instabilities of flow in them.

Decreases in mixed layer photosynthesis and CaCO3 production are termed "dead ocean" conditions by Baes (1982). I have applied the "dead ocean" concept to K-T mixed layer conditions brought about by the collapse of the coccolithophorids (McLean, 1985a).

Start/stop injections of volcanic CO2 into the marine mixed layer would have kept calcareous microplankton in continual overshoot/collapse modes. This erratic behavior of the Williams-Riley pump would have affected all other surficial feedback systems for the duration of the Deccan Traps volcanism.
Three C-13/O-18 anomalies in the final 106 years of the Maastrichtian that correspond to the extinctions of the Inoceramids, the Ammonites, and the calcareous microplankton at the K-T (Mount et al., 1986; Margolis et al., 1987), were likely a function of flow rate instabilities corresponding to early pulses of eruptions of the Deccan Traps volcanism.

Stressed conditions in the marine mixed layer continuing for at least 0.5 Ma years into Early Tertiary have been referred to as "Strangelove" oceans (Hsu and McKenzie, 1985). Strangelove conditions together with relatively low C-13 and O-18 values, changes in terrestrial floras, and terrestrial reptilian extinctions were coeval with the Deccan Traps. The combination of the Deccan Traps volcanism and failure of the Williams-Riley pump, together, triggered a major K-T carbon cycle perturbation transition into chaos.

Physicochemical killing mechanisms must be coupled to the biochemistry of the organisms that became extinct. The marine extinctions at, and immediately about, the marine K-T boundary involved mostly CaCO3-producing planktonic microplankton (coccolithophorids and foraminifera). Those organisms are pH sensitive, the former having problems at a pH of 7.3-7.0, and the latter at a pH of 7.8. A gradual lowering of pH, via injection of volcanic CO2 into the mixed layer, would, theoretically, have affected the foraminifera first, and the coccolithophorids later (McLean, 1985 b); theory accords with the record. Oscillatory pH changes caused by start/stop pulses of volcanism would have severely stressed the calcareous plankton for the duration of the Deccan Traps volcanism.

For terrestrial dinosaurian extinctions, I have advocated temperature-reproductive physiology coupling (McLean, 1978). Concurrent with my work on the K-T extinctions, I have studied the Pleistocene-Holocene mammalian extinctions via effects of variations of ambient air temperature (AAT) upon blood flow to the female mammal uterine tract. Uterine blood flow (UBF) is a developing embryo's source of oxygen, water, and nutrients and, by carrying heat away from the embryo, maintains optimum temperature for the embryo. High environmental temperatures reduce UBF, damaging, or killing, developing embryos; elevation of the uterine tract temperature above optimum by 1.5o C in modern cattle kills most embryos. I am applying this knowledge to vertebrate bioevolution (McLean, 1981c, 1986). AAT-UBF coupling operates not only in mammals, but also in birds, and reptiles. I propose that the AAT-UBF coupling was a factor in the K-T dinosaurian extinctions. Instability caused by fluctuating S-E-S would exacerbate AAT-UBF problems.

During Early Tertiary, after the Deccan Traps mantle plume fluctuation became damped by general mantle convection, came order out of chaos.

About the Author

Dewey M. McLean has backgrounds in both geology and biology (Ph. D., Stanford University; all course work for the Ph. D. in botany, University of Missouri at Columbia), 19 years directing a Cretaceous-Tertiary marine paleoalgology graduate program, and experience in the oil industry, etc. For the past decade, his primary activities have involved multidisciplinary integrative analyses, via system dynamics methodology, in exploring the roles of Earth's thermal evolution, and orbital dynamics, in evolution of the biosphere.

Acknowledgements

I thank Dr. Robert M. Norris, President of the NAGT, for the invitation to both participate in the stimulating "NAGT Symposium: Time, Life, and the Rock Record: New Implica-tions for Instruction," and to write this paper for the Journal of Geological Education.

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