Dinosaur Deccan Traps Volcanism Extinction Theory
The earliest dinosaurs appeared on earth about 230 million years ago during the geological Triassic Period, and for the next 164 million years evolved into an amazing diversity of life forms. Then, about 66 million years ago they were swallowed up in a mysterious global mass extinction event that ravaged Earth’s lands and oceans. So dramatic was the mass extinction that it defines the geological boundary between the older Mesozoic Era, the “Age of Reptiles,” and the modern Cenozoic Era, the “Age of Mammals.” On a finer geological scale, that event is called the Cretaceous-Paleogene (K-Pg) mass extinctions, or, informally, the Cretaceous-Tertiary (K-T) mass extinctions. Re usage of Paleogene versus Tertiary the GeoWhen website at //www.stratigraphy.org/bak/geowhen/TQ.html states:
"To bring clarity to these issues, the International Commission on Stratigraphy ultimately decided that the simplest solution was to do away with the terms Tertiary and Quaternary. So now the Cenozoic will formally be divided into only the Paleogene and Neogene periods, with the Neogene having been designated as continuing until the present. This avoids much of the historical ambiguity and confusion, and provides a clear roadmap for scientific use. Unfortunately, this also means losing terminology with nearly 250 years of history. Somehow, it doesn't seem likely that there will be a rush to abandon the term "Tertiary" in popular use. For example, it will probably be a long time (if ever) before the extinction of the dinosaurs at the Cretaceous-Tertiary (or KT) boundary becomes associated with the "Cretaceous-Paleogene" (or KPg) boundary."
Because older papers typically referred to the extinction event as the Cretaceous-Tertiary (K-T) extinctions, I will use that terminology liberally throughout this paper.
To examine how the Paleogene and Tertiary periods correlate with one another, time wise, please see the Geological Society of America 2009 Geological Time Scale.
More broadly, today we live in the geological Phanerozoic Eon. It is divided into three eras: the old Paleozoic Era, the intermediate Mesozoic Era, and the modern Cenozoic Era. The boundaries between the eras are defined on the basis of mass extinctions.
The mass extinction that defines the boundary between the Paleozoic and Mesozoic eras was the greatest of all mass extinctions. On a finer scale, it defines the boundary between the Permian (geological symbol, P) and Triassic (Tr) periods. Referred to as the Permo-Triassic extinctions, those extinctions coincided with the Siberian Traps mantle plume flood basalt volcanism, the greatest such event in earth history.
The Cretaeous-Paleogene extinctions coincided closely with the duration of the massive Deccan Traps mantle plume flood basalt volcanism in India. Please see the abstract to the recent paper, "U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction," by Blair Schoene, Kyle M. Samperton, Michael P. Eddy, Gerta Keller, Thierry Adatte, Samuel A. Bowring, Syed F.R. Khadri, and Brian Gertsch (Science, 11 December, 2014) further down the page.
Noteworthy is the fact that two of the three greatest mass extinctions in the geological record--those at the Paleozoic and Mesozoic eras boundary, and those at the Mesozoic and Cenozoic eras boundary--coincided with the greatest episodes of flood basalt volcanism in the geological record.
Exotic beasts, the dinosaurs and, as some scientists believe, they met an exotic end. In fact, stories written in the rocks at the time of the K-T extinctions speak of a K-T world of chaos, and great dying on the lands and in the seas. In that chaos, organisms that could tolerate the environmental conditions of the brave new K-T transition world survived into the modern Cenozoic Era. Those that could not disappeared into the mists of antiquity and extinction that ended the older Mesozoic Era. Thus did the dinosaurs become extinct.
What natural event might have triggered the K-T chaos, and extinctions? Down through the years, many scientists developed theories to account for the K-T, and dinosaurian, extinctions. They ranged from impacts of asteroids or comets with earth; volcanism; falling sea level; diseases; depletion of oxygen in the atmosphere, accumulation of carbon dioxide in the atmosphere, depletion of ozone in the atmosphere, evolution of plants that caused the dinosaurs to become constipated, or vice versa; the dinosaurs becoming so large that they could no longer reproduce, and on and on. Some of these ideas were good ones that required only the emergence of new data to test their potential validity. Any modern theories can only be developed upon the foundations laid by earlier ones.
Today, of all the theories ever developed to account for the K-T extinctions, two have become dominant. They are the impact extinction theory which advocates impact of an asteroid or comet with earth, and the Deccan Traps mantle plume extinction theory which is based on one of the greatest episodes of flood basalt volcanism in earth history. The former was originated by the Berkeley Alvarez team, spearheaded by the Nobel Laureate, Luis Alvarez.. The Deccan Traps volcanism extinction theory was originated by the author. The impact vs. Deccan Traps volcanism debate began in May 1981 at the K-TEC II meeting in Ottawa, Canada, where I first debated the Alvarez team (Russell, D. A., and Rice, G., 1982, K-TEC II: Cretaceous-Tertiary Extinctions and Possible Terrestrial and Extraterrestrial Causes: Syllogeus Series 39, National Museums of Canada, Proceedings, May 1981 workshop, 151 pp).
Prior to the above-cited meeting I had proposed the Deccan Traps volcanism as the cause of the K-T mass extinctions, and release of the K-T boundary iridium onto earth's surface during the Cretaceous-Paleogene transition, at the American Association for the Advancement of Science at its Toronto, Canada, 147th National Meeting in January 1981(McLean, D. M., 1981a, Terminal Cretaceous extinctions and volcanism: American Association for the Advancement of Science, 147th National Meeting, Abstracts of papers, p.128).
The presence of the chemical, iridium, at the K-T boundary was claimed by Alvarez to be proof of extraterrestrial impact. I equivocated the Alvarez impact theory by proposing that the iridium was due to its release upon earth's surface by the Deccan Traps mantle plume that seemed to have originated at earth's core-mantle boundary (most iridium on earth is located in earth's core). That meeting then became an abusive one with threats upon my career if I publicly opposed the asteroid theory. Alvarez, and his cronies who were proposing that asteroid impacts drive evolution on planet earth, injected their politics into the geology department where I worked with devastating impact on my career and health. For some details, please see Politics of Science Version: Click to Enter.
I next met Luis Alvarez at the October, 1981, Snowbird Meeting in Utah where I presented the only volcanic opposition to the Alvarez impact theory (McLean, D. M., 1981b, Diachroneity of the K-T contact and of the dinosaurian extinctions: National Academy of Sciences and Lunar and Planetary Institute Conference on "Large Body Impacts and Terrestrial Evolution: Geological, Climatological, and Biological Implications," abstract, p. 36).According to the impact theory, the crash of a giant asteroid, or comet, onto earth’s surface blasted so much dust into the atmosphere that it blocked out sunlight and plunged earth into darkness and cold of an "impact winter." Other speculations are impact dust and soot from raging wildfires turned earth dark and cold, and then warm, and washed giant tidal waves over earth's surface.
Re the Deccan Traps volcanism theory, a gargantuan episode of mantle plume flood basalt volcanism in India flooded earth’s surface with the greenhouse gas, carbon dioxide that served as fluctuations that grew into the structure-breaking waves of chaos of altered energy flow, chemical changes, and greenhouse climatic warming. Radically different, the impact and volcano theories are the essence of opposites, or thematic antitheses.
The primary thrust of my research since the 1970s has been to couple bioevolution and extinctions to variations in earth's carbon cycle. I am interested in all phenomena that can trigger changes in the carbon cycle, be they impacts, volcanism, or otherwise. To read my "Proposed Law of Nature Linking Impacts, Plume Volcanism, and Milankovitch Cycles to Terrestrial Vertebrate Mass Extinctions via Greenhouse-Embryo Death Coupling," that I presented at the conference titled New Developments Regarding the KT Event and Other Catastrophes in Earth History (Houston, Texas, 1994), please click on McLean (1994). I have concentrated on the Deccan Traps volcanism involvement in the K-T extinctions because such huge and long-duration volcanic events release prodigious amounts of the greenhouse gas, carbon dioxide, onto earth's surface.
It is with the greatest interest that I follow the latest research on the Deccan Traps involvement in the K-T extinctions by Professor Gerta Keller at Princeton and her associates, and especially so because for 15 years she worked to confirm the Alvarez impact extinction theory, but was finally won over by evidences opposing it. Please see her fascinating article titled "Deccan Traps Eruptions Killed Off Dinosaurs, not the Chicxulub Asteroid" (November 2011) at //askwhy.co.uk/dinosauroids/?p=11366. Following are some quotations from the article:
Despite Keller having spent 15 years trying to confirm the impact hypothesis, she found increasing evidence against it. So she is now a prominent opponent of the Chicxulub impact as an adequate agent of mass extinction. She led a team which announced in 2003 that a sediment core from the Chicxulub crater showed the impact predated the mass extinction by about 300,000 years...None of the other great mass extinctions are associated with an impact, and no other large craters are known to have caused a significant extinction event.
Keller is among those who accept the 30 year old idea of geologist Dewey McLean that Deccan Traps volcanism was the source of the Cretaceous mass extinction...Keller's teams have collected compelling evidence to support McLean.
Vincent Courtillot, a geophysicist and professor at Paris University Diderot, found that Deccan vulcanism happened in three phases. The first and weakest began roughly 2.5 million years before the second phase eruptions, around 67.5 million years ago. The second and largest phaseDeccan phase-2coincided with the KT mass extinction. It accounted for 80 percent of the total volcanism and produced the largest lava flows in Earth’s history...The less severe third phase of Deccan activity began about 300,000 years after the KT mass extinction inhibiting species recovery for the next 500,000 years.
NOTE: A great advance in understanding the cause of K-T mass extinction event was made by the publication of the recent paper, "U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction," by Blair Schoene, Kyle M. Samperton, Michael P. Eddy, Gerta Keller, Thierry Adatte, Samuel A. Bowring, Syed F.R. Khadri, and Brian Gertsch (Science, 11 December, 2014). Following is the abstract from the Science article:
"The Chicxulub asteroid impact (Mexico) and the eruption of the massive Deccan volcanic province (India) are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of nonavian dinosaurs. Despite widespread acceptance of the impact hypothesis, the lack of a high-resolution eruption timeline for the Deccan basalts has prevented full assessment of their relationship to the mass extinction. Here we apply U-Pb zircon geochronology to Deccan rocks and show that the main phase of eruptions initiated ~250,000 years before the Cretaceous-Paleogene boundary and that >1.1 million km3 of basalt erupted in ~750,000 years. Our results are consistent with the hypothesis that the Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions."
Re chemical changes at and around the K-T boundary, Günther Graup of the Max-Planck Institut Für Chemie, stated in a 17 February 1992 letter to me:
From our results I further believe that you are fully correct all over the years with your conclusion that the increased CO2 input from volcanoes into atmosphere and oceans would finally overcome the carbonic acid buffer system in ocean waters. The tilting of a buffer system, of course, would look like an instantaneous event although it was initiated long before. The concomitant slow decrease in pH would then result in the successive precipitation of elements observed now as stratification.
It was over four decades ago, in the late 1960s, that I first began researching the cause of the Cretaceous-Paleogene transition mass extinction event of 66 million years ago, during which the dinosaurs disappeared. At that time I was a doctoral student at Stanford University in Bill Evitt's palynology program working on my dissertation on Early Tertiary dinoflagellates from the Atlantic Coastal Plain of Virginia. The fossils I worked on had lived in the oceans just after the extinction event and my research led me into the extinctions literature. What I discovered there so captivated me that it started me on a scientific odyssey that came to consume much of my later academic career.
In the literature, I discovered from Milton Bramlette’s paper “Massive Extinctions in Biota at the End of Mesozoic Time” (1965) that right at the KT boundary, the marine microscopic fossils known as coccolithophorids had undergone massive extinctions. The extinction triggering mechanism was not known. Helen Tappan’s paper “Primary production, isotopes, extinctions and the atmosphere” (1968), that linked atmospheric and oceanic oxygen/carbon dioxide ratios to marine algal productivity through time expanded my world by showing me how to use marine algae to study global climatology and extinctions. Norman Newell’s paper “Paleontological Gaps and Geochronology (Journal of Paleontology, 1962), and “Mass Extinctions at the end of the Cretaceous Period” (Science, 1965) further instructed me on the KT world. M. W. De Laubenfels’s paper, “Dinosaur extinction: one more hypothesis” (1956), the first to suggest that a meteorite colliding with earth had triggered the KT extinctions, piqued me to think about the role of extraterrestrial events in earth history. And a book by Angus d’A. Bellairs titled Reptiles: Life History, Evolution, and Structure (1960) introduced me to the influence of climatic warming upon physiology as a factor in reptilian extinctions. Out of my Ph.D. experience at Stanford, my career ambitions expanded to include study of the role of climate change in bioevolution and extinction.
The strata I worked on for my Ph.D. dissertation at Stanford were from the Atlantic Coastal Plain of Virginia. The Atlantic Coastal Plain is a broad band of Cretaceous and Tertiary strata exposed along the eastern margin of the United States, that stretches from New Jersey into Georgia. These strata plunge under the Atlantic Ocean as the Continental Shelf. I hoped to find a teachingresearch position near to the Atlantic Coastal Plain so that I could develop both a palynological program on those strata, and also a theoretical research program.
Byron Cooper, then head of the Department of Geological Sciences at the Virginia Polytechnic Institute (VPI, later called Virginia Tech) in Blacksburg, Virginia, invited me to interview at VPI. He listened to my dreams of using marine phytoplankton to study the role of climatology in bioevolution and extinctions, and made me a job offer. In a follow-up letter, before I accepted, Cooper stated, "What you do here will be left largely to you to develop." Dick Jahns, Dean of the Stanford School of Earth Sciences, had recently served on an advisory panel to VPI geology, and spoke so highly of it that I accepted the offer. In January 1969, I began work at VPI laying foundations for a graduate research program on Cretaceous and Tertiary marine dinoflagellates along the Coastal Plain that, in time, would expand from New Jersey to into Alabama, and into research on cause of the K-T extinctions.
The late 1960s and early 1970s were an exciting time for me. The Continental Shelf along eastern margin of the United States offered hope for oil reserves. The oil companies were booming, and marine dinoflagellates, which are useful for age dating and correlation of marine strata, were a hot topic. Because the Coastal Plain strata extend under the Atlantic Ocean as the Continental Shelf, I felt that my graduate research research program on Coastal Plain dinoflagellates would help oil explorations of the latter. Those were exciting times, and my graduate students were in excellent demand and while necessity dictated that I give most of my attention to my dinoflagellate program, I expanded my work into paleoecology and paleobiology via research in a couple of dozen fields of science that I deemed critical to developing holistic comprehension of K-T dynamics. They span the Cretaceous and Tertiary fossil records (animal and plant, marine and terrestrial), biostratigraphy, physical stratigraphy, plate tectonics, carbon cycle, stable isotopes, mantle processes that include degassing, paleobiology, paleoecology, climatology, oceanography, biochemistry, solar-earth-space energy flow systems, and system dynamics, to name some.
Doing descriptive paleontology where one can actually pick up and handle fossils, or examine them through the microscope, and measure their physical parameters, is relatively straightforward. However, trying to find meaning in a world 66 million years old, where many of the critical data were missing, is not. I quickly realized that finding cause of the KT extinctions must involve searching for unifying methodologies that would allow meaningful integration of the massive data base I had accumulated via study of nearly a couple dozen branches of science. nature that govern how variations in natural earthly processes might affect bioevolution and extinction. But how does one do that? I combed through the philosophy literature for advice on methodology on how to search for universalities, and studied the works of Karl Popper, Thomas Kuhn, Imrie Lakatos, among others.
I found the scientific approach I needed in the philosophy of the great physicist, Albert Einstein. Einstein taught that “to elementary laws there leads no logical path, but only intuition, supported by being sympathetically in touch with experience.” And that theories into which facts were later seen to fit are more likely to stand the test of time than theories made up entirely from experimental evidence. And that one must never be satisfied with his own theories, and must probe them for weak spots to find their limitations, and be willing to give them up in the face of overwhelming contradictory evidence. And that all theories are ever tentative, hypothetical, or conjectural. Einstein’s philosophy gave me method and courage to seek principles and laws of nature in a largely unknown world 66 million years old, in which most critical information was lacking.
Other scientists provided scientific methodologies that expanded my research. Harold Morowitz’s book Energy Flow in Biology (1979) opened my thinking into how energy flow through systems organizes them. Jay W. Forrester’s book Principles of Systems (1968) introduced me to the world of systems and how to study them. Ilya Prigogine and G. Nicolis' book, Self-Organization in Non-Equilibrium Systems (1977), provided methodology to systems... conceive how thermal evolution of the earth, itself, influences evolution of earth’s biosphere. Jason Morgan’s work on mantle plumes, and specifically the Deccan Traps mantle plume, was to influence my work on coupling the Deccan Traps mantle plume volcanism in India to a KT greenhouse, and the KT extinctions, and to propose that iridium enrichment at the KT boundary was released onto earth’s surface by the Deccan Traps volcanism. Frank Gwazdauskas, whose pioneering work on how environmental heat reduces the flow of blood to the female uterine tract, where embryos develop, allowed me to couple that mechanism directly to climate and to develop a greenhouse physiological killing mechanism.
Effects of a Major Carbon Cycle Perturbation
In the oceans, warming, and acidification of the upper waters as atmospheric carbon dioxide diffuses into them, can kill life on a massive scale. For example, warming of Pacific Ocean waters during modern El Niño events devastate marine life. I proposed the first research that I know of linking global greenhouse climate change to extinctions (McLean, D. M. 1978, A terminal Mesozoic "greenhouse": lessons from the past: Science, v. 201, p. 401-406). In 1979, I proposed the first work coupling the direct effects of elevated environmental heat upon mammalian female uterine blood flow, which damages and kills developing embryos and, I believe can trigger extinctions among vulnerable populations (McLean, D. M., 1979, Global warming and late Pleistocene mammalian extinctions: Geological Society of America, Southeastern Section meeting, Abstracts, p. 205). Based on my long studies of the impact of greenhouse warming upon life, I believe that a major perturbations of the carbon cycle serve as fluctuations that invade earth's surficial systems, including the biosphere (the thin and patchy film of life scattered over earth's surface), triggering transition from order to chaos, and collapse of vulnerable systems, and extinctions. I believe that such times of chaos are the most dangerous phenomenon that life of our planet earth can experience. Today, because of our burning of the fossil fuels coal, oil, and gas, which is releasing prodigious amounts of carbon dioxide into the atmosphere where it traps heat from the sun that can trigger greenhouse climate change, our civilization faces the prospects of a major dangerous climatic warming.
Lessons from the Past
Part of my work on ancient extinctions is to lay foundations for assessing how a modern greenhouse climate change might affect our civilization. Today, our burning of the fossil fuels coal, oil, and gas is like a human volcano that is releasing vast amounts of carbon dioxide into the atmosphere. Many scientists fear that the carbon dioxide build up in the atmosphere will trigger a modern greenhouse climate change. Others welcome a modern greenhouse, claiming that it will benefit our civilization. Those latter people do not seem aware that the reproductive systems of modern mammalsincluding humansare easily damaged by environmental heat. Today, the heat of normally hot summer days is already destroying vast numbers of mammalian embryos on a global scale. Any additional heat load imposed by a greenhouse can only kill increasing numbers of embryos.
Most people do not know that today we live in a hot interglacial world, one in which many organisms may already exist dangerously near to their upper thermal limits for species survival. To examine how we modern mammals fit into this hot world, and how a climatic greenhouse might affect our civilization, please see my paper "A Climate Change Mammalian Population Collapse Mechanism" that I presented at the conference titled Energy and Climate (Helsinki, Finland, 1991). To read the paper, please click on McLean (1991). To read my paper, "Embryogenesis Dysfunction in the Pleistocene/Holocene Transition Mammalian Extinctions, Dwarfing, and Skeletal Abnormality," that I presented at the Symposium on the Quaternary of Virginia (Charlottesville, Virginia, 1984), please click on McLean (1986). To read my paper, "Greenhouse Warming and Mammals: Analogues and Consequences," that I presented at the Global Change: A Southern Perspective Conference (Charleston, South Carolina, 1990), please click on McLean (1990). To read my Senate Hearing testimony, "Climatic Warming and Mammalian Evolution/Extinctions" (The Global Environmental Protection Act of 1988, Washington, D.C.), please click on McLean (1988).
Origins of the Impact and Volcano-Greenhouse Theories
Origin of the Impact Theory
The Alvarez team began developing its K-T impact theory in the mid-late 1970s. The impact theory originated in geological field work by Walter Alvarez, son of the Nobel physicist, Luis Alvarez, near Gubbio, Italy. Walter showed his father a hand sample of the K-T boundary in which a clay layer several centimeters thick separated Late Cretaceous and Early Tertiary limestones. They enlisted the help of nuclear chemists Frank Asaro and Helen Michels who discovered that the clay was enriched in iridium, an element that is rare in earth's crustal rocks. Because some extraterrestrial objects are enriched in iridium, Luis Alvarez proposed that a gigantic asteroid hit Earth 66 million years ago. Theoretically, the impact blasted so much dust into the atmosphere that it blocked out sunlight, plunging Earth into blackness and cold (later called an "impact winter") that triggered the K-T mass extinctions (Alvarez et al., 1980). The dust from the impact supposedly settled out as the iridium-rich K-T boundary clay.
According to Alvarez theory, the global blackout triggered extinctions among the plant kingdom, and then among herbivores that depended upon plants for food, and then among the carnivores that ate the herbivores. In fact, a case can be made that the Alvarez killing mechanism was lifted from Bill Napier and Victor Clube's concept of an impact-induced global blackout published in a paper titled "A Theory of Terrestrial Catastrophism" (Napier and Clube, 1979). For other impact killing mechanisms, Clube and Napier also proposed blast effects analogous with nuclear explosions and tsunamis, that other scientists later evoked. Other scientists later expanded the impact killing mechanisms to include greenhouse warming, and impact-induced global wildfires that burned down most of earth's forests, for which there is no definitive evidence.
The primary global-scale impact killing mechanism is an impact winter. At the time Alvarez et al. published their impact theory in 1980, I had already proposed that a major perturbation of earth's carbon cycle unified the K-T geobiological record, including the mass extinctions. I published my findings in a paper titled "A Terminal Mesozoic Greenhouse: Lessons from the Past" (Science, 1978). For the K-T terrestrial extinctions (including the dinosaurs), I proposed climatic heat-induced reproductive failure (discussed later in this website), and for the marine extinctions a combination of pH change and warming. To read this paper please click on McLean (1978).
In 1980, I began searching the K-T geobiological record for evidences of a K-T boundary impact winter. A decade of search did not produce definitive evidences of a K-T boundary blackout and refrigeration. I presented my findings at a Chapman Conference of the American Geophysical Union titled Global Biomass Burning: Atmospheric, Climatic, and Biospheric Implications. My paper, "Impact Winter in the Global K/T Extinctions: No Definitive Evidences," can be read by clicking on McLean (1991).
Today, impactors claim that the Chicxulub structure on Yucatan marks the impact site of the "K-T killer." However, the age of the Chicxulub structure (older, the same, or younger than the time of the K-T boundary) is controversial.
For readings on the origin and development of the Alvarez theory see Luis Alvarez's book titled Alvarez: Adventures of a Physicist (1987), Walter Alvarez's T. rex and the Crater of Doom (1997), and Peter Trower's Discovering Alvarez (1987).
Origin of the VolcanoGreenhouse Theory
I first began studying the K-T extinctions while a Ph.D. student at Stanford University in the mid-late 1960s. My dissertation was on a type of microscopic marine phytoplankton known as dinoflagellates that had lived in the world's oceans soon after the K-T boundary extinctions. My readings took me into the K-T extinctions literature which whetted an interest in the cause of the extinctions. In 1969, I began developing a graduate research program at Virginia Tech on Cretaceous and Tertiary dinoflagellates on the Atlantic Coastal Plain along the eastern margin of the United States. By the middle 1970s, I was expending major time and effort on the cause of the K-T extinctions.
In my graduate program, we often worked along the K-T boundary. My theoretical work on the K-T extinctions grew out of my research program. For the K-T extinctions, I began by examining them within the context of variations in earth's carbon cycle. This seemed a good place to begin my theoretical research into an ancient world 66 millions years distant, about which precious little reliable information existed. The late, great, Roger Revelle (1985) had to this to say about carbon dioxide:
Carbon dioxide may be thought of as the most important substance in the biosphere: that part of the earth's atmosphere, hydrosphere,and solid crust in which life exists. It has supported the existence and development of life by serving as the source of carbon, the principle element of which all living things...are made. In past times it was a source of the free oxygen in the air and the ocean that makes animal life possible. By absorbing and backscattering the heat radiated from the earth's surface, it maintains, together with atmospheric water vapor, a sufficiently high temperature in the air and the sea to allow liquid water, and therefore life, to exist. Earth's uniquely benign environment for living things depends fundamentally, of course, on its relationship to a small, steady star, the sun; but this relationship is modulated in essential ways to carbon dioxide.
My approach to the searching for cause of the K-T extinction was to integrate elements of many branches of science to search for principles and laws of nature that influence bioevolution and extinction on our planet. The branches included: elements of the Cretaceous and Tertiary fossil records (animal and plant, marine and terrestrial, microscopic and megascopic), biostratigraphy, physical stratigraphy, plate tectonics, the carbon cycle, stable isotopes, internal earthly processes that include mantle degassing, paleobiology, paleoecology, climatology, oceanography, biochemistry, the solar-earth-space energy flow system, and system dynamics, to name some.
Knowledge of geological time-rock relationships is critical because they can create the illusions of instantaneous, catastrophic, extinctions where none occurred. Compounding the complexity, missing strata at the K-T boundary in most places has destroyed the data most critical to testing theories. Rebuilding the K-T transition world is like trying to assemble a gigantic jigsaw puzzle that has most of its pieces missing. Limitations confound us at every turn. For example, theories that evoke sudden, catastrophic, extinctions simply cannot be tested from the actual geobiological record because the K-T boundary rocks are usually missing at most localities.
By 1977, I had come to suspect that 66 million years ago, at K-T boundary time, earth experienced a major perturbation of the carbon cycle that unified the K-T geobiological record, including the mass extinctions. I published my findings in a paper titled "A terminal Mesozoic greenhouse: lessons from the past" (Science, 1978). For the K-T terrestrial extinctions (including the dinosaurs), I proposed climatic heat-induced reproductive failure (discussed later in this website), and for the marine extinctions a combination of pH change and warming. To read this paper please click on McLean, 1978.
In 1979, I began coupling the K-T carbon cycle perturbation to the Deccan Traps mantle plume volcanism in India, one of the greatest episodes of volcanism in earth history. In January 1981, at the AAAS National Meeting, Toronto, Canada, I proposed that the Deccan Traps volcanism triggered a major K-T carbon cycle perturbation, released the K-T boundary iridium onto Earth's surface, and caused the K-T mass extinctions. My abstract which was titled "Terminal Cretaceous Extinctions and Volcanism: a Link" can be read at: McLean (1981).
The Deccan Traps volcanism was one of the greatest episodes of mantle plume volcanism in Earth history, and the vast bulk of its lavas erupted right at K-T boundary time. The duration of its eruptions was coeval with major shifts in the carbon and oxygen stable isotope records, "Strangelove conditions" in the oceans, and the K-T bioevolutionary turnover. In addition, it occurred simultaneously with other phenomena such as marine transgression, reduced photosynthesis of terrestrial and marine floras, and reduced weathering rates that would all have contributed to producing a major trans-K-T perturbation of the carbon cycle (McLean, 1995).
In the broadest sense, the state of the biosphere at any time is a function of the rate of flow of energy from the sun to earth, and on to outer space. Variations in the carbon cycle influence the solar-earth-space (S-E-S) flow rates. Great volcanic events release greenhouse gases (water vapor and carbon dioxide) onto earth's surface, thus influencing the carbon cycle, and the S-E-S flow system. Thus, volcanism exerts control upon the state of earth's biosphere in ways to influence bioevolution and extinction. So vast was the Deccan Traps volcanism that it would have flooded earth's surficial systems with carbon dioxide faster than they could have absorbed it, creating fluctuations that would have grown into structure-breaking waves that would have invaded and destabilized them, forcing life to change, or become extinct. Some forms of life, such as the dinosaur could not do so, and became extinct. To examine how earth's systems are interconnected such that changes in one might affect others see the Holistic Earth Causal Loop Diagram.
Also in 1979, I isolated a physiological mechanism that links variations in earth's climate directly to vertebrate population dynamics, and thus to bioevolution and extinction. My abstract, "Global Warming and Late Pleistocene Mammalian Extinctions" can be read at McLean (1979). [For more details please see the text of A Climate Change Mammalian Population Collapse Mechanism (McLean, 1991) and Greenhouse Vertebrate Physiological Killing Mechanism. This mechanism works for mammals, reptiles, and birds, and shows how times of rapid greenhouse climatic warming can trigger global scale extinctions.]
Linking variations in the carbon cycle to a physiological mechanism by which climate influences population dynamics provides what I believed is a universal mechanism that exerts control upon vertebrate bioevolution and extinctions through geological time. Basically, I am interested in all phenomena that can trigger perturbations of the carbon cycle sufficiently to triggered changes in earth's life, and that includes impact events. If a K-T boundary impact can be shown to be linked meaningfully to the extinctions, I will accept it, and go on with my work. (Please see Proposed Law of Nature Linking Impacts, Plume Volcanism, and Milankovitch Cycles to Terrestrial Vertebrate Mass Extinctions via Greenhouse-Embryo Death Coupling [McLean, 1994]).
In May 1981, the impact and volcano-greenhouse theories met and crashed head-on at the K-TEC II (Cretaceous-Tertiary Environmental Change) meeting in Ottawa, Canada. That meeting marks the origin of the K-T impact versus volcanism extinctions debate. My abstract for that meeting which was titled "Deccan Volcanism and the Cretaceous-Tertiary Transition Scenario: A Unifying Causal Mechanism" can be read at: McLean (1981). A word for word coverage of the K-TEC II meeting can be found in K-Tec II Cretaceous-Tertiary Extinctions and Possible Terrestrial and Extraterrestrial Causes: Syllogeus Series 39, National Museums of Canada (Proceedings, May 1981 workshop), Russell, D. A., and Rice, G., eds., 151 pp.
The VolcanoGreenhouse Theory
Deccan Traps Mantle Plume Volcanism
In Late Cretaceous time, India was an isolated land mass drifting northward toward its collision with Asia. While India was east of Madagascar, and just south of the equator, it drifted over the head of a mantle plume. Mantle plumes are columns of buoyant molten rock material which rise through earth's mantle. They burn through the lithosphere plates to erupt as "hotspot" volcanos. Mantle plume volcanos release great volumes of basaltic lavas onto earth's surface. This type volcanism is also known as flood basalt volcanism because the relatively liquid lavas flood out over vast geographical areas. Click here for an enlarged view. Click here for an enlarged view.
Earth's outer portion is divided into several large, rigid, lithosphere plates, and numerous smaller ones. Convection in the mantle causes the plates to drift about on earth's surface relative to one another. Some plates support continents, and some do not. Plate movement can be up to several inches per year. The lithosphere plates are composed of from 20 to 100 km of outer mantle and, where present, continents.
Movement of the lithosphere plates over a stationary mantle plume produces chains of volcanos. The Hawaiian Island chain of volcanic islands in the Pacific Ocean is an example. These chains of volcanos are also known as hotspot tracks. Morgan (1981) relates the Deccan Traps volcanism to a hotspot volcano on Reunion Island in the Indian Ocean, about 700 km east of Madagascar. The hotspot is first indicated beneath India, with the bulk of the Deccan Traps lavas erupting at the time of the K-T extinctions. The track progresses along the Laccadive, Maldive, and Chagos Islands; the Carlsberg Rise migrates over the hot spot; and the track makes the southern part of the Mascarene Plateau, and the islands of Mauritius, and Reunion Island.
The hotspot volcano that produced the Deccan Traps lava pile still exists today on Reunion Island in the Indian Ocean. Known as Piton de la Fournaise, it is one of the world's most active volcanos with more than 100 eruptions in the past 300 years. The graphic to the left is an SIR-C (Spaceborne Imaging Radar) image of Reunion Island. This image was acquired by the Spaceborne Imaging Radar-C/X- Band Synthetic Aperture Radar (SIR- C/X-SAR) aboard the space shuttle Endeavour on October 5, 1994. The volcano Piton de la Fournaise is visible in the lower portion of the image. The area shown is about 50 km by 80 km. North is toward the upper right. (The graphic is used with the permission of Dr. R. B. Trombley of the Southwest Volcano Research Centre, Apache Junction, AZ. The detailed information on Reunion Island is from the website at //www.jpl.nasa.gov/radar/sircxsar/renis.html.) Click here for an enlarged view.
Incidentally, Piton de la Fournaise is still releasing the chemical, iridium--that provided the original basis for the impact theory--into the atmosphere today. I believe that the Deccan Traps volcanism released the K-T boundary iridium onto earth's surface.
About 66 million years ago, the mantle plume that gave rise to the Reunion hotspot volcano burned its way through earth's crust, flooding western India and surrounding areas with the Deccan Traps flood basalts. Deccan Traps basaltic lavas ultimately covered a large portion of India under successive horizontal lava flows, converting it into an immense volcanic plateau. The name Deccan Traps comes from the Terrace-like profile resulting from successive flows, "Deccan" from dakhan (= south), and "traps" from the Swedish trapp, trappa (= stair). The original lava coverage (in red) may have exceeded one million km2 (Krishnan, 1960). Pasco (1964) suggested that the original coverage of the Deccan Traps and related lavas was greater than 2.6 million km2. Today, after 66 million years of erosion, the lavas (in black) still cover 500,000 square kilometers, and are a mile and a half thick in western India. Click here for an enlarged view.
A great rift known the Narmada Son, extends east-west across India. Seismic data indicate that it crosses the Moho into the mantle. When the Narmada Son rift passed over the Deccan Traps plume head, basaltic lavas flooded through over vast geographical areas. According to Basu et al., 1993, and Basu, pers. comm.), about 90 percent of the vast Deccan Traps erupted right at K-T boundary time 66 million years ago, pouring out its vast volume of lavas in 100,000 to 200,000 years.
Rapid eruption of the vast Deccan Traps lava fields would have flooded earth's surface with CO2, overwhelming surficial systems and sinks, triggering rapid K-T transition greenhouse warming, chemical changes in the oceans (McLean, 1985a, b, c; 1988, 1995), and the K-T mass extinctions.
To read my paper "Deccan Traps mantle degassing in the terminal Cretaceous marine extinctions" (Cretaceous Research, 1985), please click on McLean (1985).
For evidence that a carbon cycle perturbation and greenhouse warming began at the same time as the Deccan Traps volcanism and persisted for the duration of the Deccan Traps volcanism, see Brazos River, Texas, Isotope Record). Other localities showing evidences of K-T transition warming are: Atlantic Ocean DSDP sites 384, 86, 95, 152, 144, 20C, 21, 356, 357, and 329; Indian Ocean DSDP sites 212, 217, 220, 237, and 253; South Atlantic DSDP site 524; Denmark; Biarritz, France; Lattengebirge, Germany; Zumaya, Spain; Caravaca, Spain; and Pacific and Atlantic Ocean DSDP sites.
K-T Boundary Iridium
In the early 1980s, the K-T boundary iridium enrichment provided the sole basis for the Alvarez impact theory. At the January 1981 national meeting of the American Association for the Advancement of Science meeting held in Toronto, Canada, I proposed that the Deccan Traps mantle plume volcanism likely released the K-T boundary iridium onto earth's surface. I did so later at the May 1981 Ottawa K-TEC II meeting, and at the October 1981 Snowbird I Conference (See References). Earth's core is rich in iridium and the Deccan Traps mantle plume, originating at earth's core-mantle interface, likely served as a conduit to transport iridium from the core to earth's surface. In fact, the hotspot volcano that produced the Deccan Traps (Piton de la Fournaise on Reunion) is still releasing iridium today (Toutain and Meyer, 1989).
Earth's Thermal Evolution as a Control of Bioevolution and Extinction
Earth is zoned into great spheres. At earth's center is the partially molten metallic core. The solid inner core is surrounded by the liquid core. Next outward are the rocky mantle, crust, hydrosphere (the waters of earth), atmosphere (the gaseous envelope that surrounds the earth), and the thin, discontinuous, patches of life which are known collectively as the biosphere. Via the 2nd Law of Thermodynamics, earth loses its internal heat to the cold outer space heat sink. This heat flow determines the direction and rate of evolution of the earth. It causes convection in the mantle which, in turn causes the continents to drift about on earth's surface. This convection also transports materials and greenhouse gases such as water vapor and carbon dioxide to earth's surface via volcanos, fumaroles, and hot springs. These greenhouse gases trap heat from the sun, allowing earth to warm sufficiently to support life. Through time, earth is losing its internal heat to outer space. As the earth loses its internal heat, the great spheres must evolve along with it. This includes the biosphere. Thus, thermal evolution of the earth, by forcing evolution of the biosphere, is a driving source of bioevolution and extinction.
Earth: A Variable Greenhouse Planet
In earth's early history while it was forming as a protoplanet, water and carbon dioxide were trapped inside it. Later, when the entire earth melted, water vapor and carbon dioxide were sweated out of earth's interior to the surface. This process is called mantle degassing. Mantle degassing continues today as volcanos, fumaroles, and hot springs release these gases into earth's atmosphere.
Water vapor and carbon dioxide in the atmosphere are called greenhouse gases because they trap heat from the sun, warming earth's surface. Because these gases are always present in the atmosphere, earth is a perpetual greenhouse planet. Without them, earth's surface would be frozen solid. As it is, earth's surface is about 30 degrees K warmer than it would be without them, allowing earth to support life. However, the greenhouse effect varies through time and, as it changes, earth's life must evolve along with it or become extinct.
Over long geological intervals, a steady state exists between release of greenhouse gases upon earth's surface and their uptake by surficial systems. At those times, relative ecological stability prevails on earth's surface. However, vast episodes of mantle plume volcanism, such as the Deccan Traps, releases vast amounts of CO2 onto earth's surface faster than it can be taken up by surficial sinks, disrupting the steady state to which earth's surficial systems are adapted, triggering a perturbation of the carbon cycle, ecological instability, and mass extinctions (McLean, 1985a, b, c).
Study of the Deccan Traps model promises to shed new light on the role of earth's thermal evolution upon the evolution of life. Most interestingly, the great Permian-Triassic mass extinction of 250 million years ago, the greatest mass extinction in earth history, coincided with the Siberian Traps volcanism in Siberia, one of the greatest episodes of flood basalt volcanism in earth history (Renne et al., 1995). The K-T and Permo-Triassic marine extinctions show striking parallels between environmental CO2 buildup and extinctions.
Fitting the K-T into Earth History
In the broadest sense, the state of the biosphere at any time is a function of the rate of flow of energy from the sun to earth, and on to outer space. Variations in the carbon cycle influence the solar-earth-space (S-E-S) flow rates. Great volcanic events release greenhouse gases (water vapor and carbon dioxide) onto earth's surface, thus influencing the carbon cycle, and the S-E-S flow system. Thus, volcanism exerts control upon the state of earth's biosphere in ways to influence bioevolution and extinction. So vast was the Deccan Traps volcanism that it would have flooded earth's surficial systems with carbon dioxide faster than they could have absorbed it, creating fluctuations that would have grown into structure-breaking waves that would have invaded and destabilized them, forcing life to change, or become extinct. Some forms of life, such as the dinosaursin the strict sensecould not do so, and became extinct. To examine how earth's systems are interconnected such that changes in one might affect others see the Holistic Earth Causal Loop Diagram.
NOTE: The Deccan Traps research is but a special theory within the general theory that variations in the carbon cycle exert control upon bioevolution and extinction.
K-T Transition into Chaos
Earth's surficial systems, including the biosphere, are open, nonequilibrium, dissipative, self-organizing structures, characterized by continuous oscillations, and self-renewal via exchanges with the environment. They are never truly stable, and must continually adjust to fluctuations from the environment. Whereas modest fluctuations may be absorbed, major environmental fluctuations above a critical threshold force systems to seek new stable configurations. Those that cannot do so cease to exist. Widespread inability to find stable configurations are times of mass extinctions. (Please see the text of my paper titled K-T Transition into Chaos [McLean, 1988]).
The state of earth's biosphere is, at any time, a function of the rate of solar-earth-space energy flow (S-E-S). The greenhouse gas composition of earth's atmosphere controls S-E-S. (See Holistic Earth Causal Loop Diagram). During the Deccan Traps volcanism, its release of carbon dioxide onto earth's surface was a massive addition to the pre-K-T steady state mantle carbon dioxide degassing to which surficial systems were adjusted. The Deccan Traps volcanic carbon dioxide fluctuation invaded surficial systems, becoming more powerful via positive feedback, shattering pre-K-T order, and triggering K-T transition into chaos (McLean, 1988a). Cessation of the Deccan Traps eruptions allowed order to again arise spontaneously out of chaos.
Evidences of a K-T Transition Greenhouse
Eruptions of 90 percent of the Deccan Traps lava pile began at K-T boundary time 66 million years ago (Basu et al., 1993). A carbon cycle perturbation and greenhouse warming began at the same time as the Deccan Traps volcanism and persisted for the duration of the Deccan Traps volcanism. (See Brazos River, Texas, Isotope Record). Other localities showing evidences of K-T transition warming are: Atlantic Ocean DSDP sites 384, 86, 95, 152, 144, 20C, 21, 356, 357, and 329; Indian Ocean DSDP sites 212, 217, 220, 237, and 253; South Atlantic DSDP site 524; Denmark; Biarritz, France; Lattengebirge, Germany; Zumaya, Spain; Caravaca, Spain; and Pacific and Atlantic Ocean DSDP sites.
Greenhouse Killing Mechanisms
Greenhouse Vertebrate Physiological Killing Mechanism
In the late 1970s, as I was developing the concept of a K-T carbon cycle perturbation, I searched for a vertebrate physiological mechanism by which to explain the extinction of the dinosaurs as a function of greenhouse climatic warming. I sought the mechanism via using dairy science reproductive physiology to study cause of the Pleistocene-Holocene mammalian extinctions during the greenhouse warming at the end of the last ice age 10,000-12,000 years ago. In 1979, I isolated a physiological mechanism involving female mammals by which environmental heat influences embryo survival, and thus population dynamics, and bioevolution and extinction. This greenhouse physiological killing mechanism involves environmental heat-induced reduction of blood flow to the uterine tract, that damages and kills embryos within their mothers (McLean, 1979, 1981c, and later). This vertebrate greenhouse killing mechanism, grounded in established dairy science reproductive physiology, also operates among mammals, reptiles, and birds. I recently extended it to the dinosaurs (McLean, 1995). (Please see the text of A Climate Change Mammalian Population Collapse Mechanism [McLean, 1991], and the Greenhouse Vertebrate Physiological Killing Mechanism. The text of my paper titled K-T Transition Greenhouse and Embryogenesis Dysfunction in the Dinosaurian Extinctions [McLean, 1995] pulls together much of my work on the K-T extinctions).
We modern mammals (including humans) are but the survivors of the Pleistocene-Holocene extinctions that occurred during the warming that ended the last ice age (see "A climate change mammalian population collapse mechanism" (McLean, 1991b). Today, we live in a hot interglacial greenhouse world in which many species likely exist near to their upper thermal limits. In this already hot world, every summer, all around us, the greenhouse physiological killing mechanism is already at work killing mammalian embryos. Because the mechanism operates silently and out of sight within pregnant females, we have not recognized the danger it poses for a modern human-generated greenhouse climatic warming. Greenhouse heat is already killing mammals on a vast global scale. Any additional greenhouse warming can only increase embryo death rates. A modern worst-case greenhouse could trigger collapse of mammalian populations in the vulnerable middle latitudes where most humans live (McLean, 1988b, Senate Hearing Testimony).
In 1994, I proposed a law of nature that couples earth's variable greenhouse to bioevolution and extinction (McLean, 1994).
K-T Marine Extinctions
The K-T marine extinctions involved microscopic plankton (floaters), swimmers, and organisms living on, or attached to, the ocean floor.
The microplanktonic coccolithophorids, CaCO3 shell producers that produced the great Cretaceous chalk deposits (e. g., the White Cliffs of Dover), suffered massive extinctions at the K-T boundary (Pospichal, 1996). These extinctions are explained via Deccan Traps volcanic CO2 injection into the upper layers of the oceans that produced "dead ocean" conditions via pH and temperature changes (McLean, 1985c). The microplanktonic dinoflagellates (organic walls) and diatoms (siliceous shells) were relatively unaffected.
For microscopic shelled animals known as foraminifera, new tran-K-T graphic correlation studies indicate that basal Tertiary stratigraphic successions display "progressive rather than instantaneous turnover in biotic, sedimentologic, and geochemical variables over at least 500,000 years." The impact "scenario fails to account for a large number of physical and biotic observations in both ancient and modern faunas and should be abandoned as a plausible model of tran-K/T events" (MacLeod, 1995).
Deccan Traps volcanic CO2 accumulation in marine waters also accounts for the trans-K-T extinction of both swimmers and organisms living on, or attached to, the ocean floor. Ward (1994) notes these extinctions commenced in phases. The earliest, just below the K-T boundary, involved inoceramid bivalves, reef facies, and other benthic mollusks. The next phase, at the K-T boundary, involved extinction of all the ammonites and the microscopic organisms discussed above. The final phase involved benthic foraminifera during earliest Tertiary time.
Accumulation of CO2 in marine waters is known to produce deleterious effects on many marine animals (Knoll et al., 1996, from which the following is abstracted). Elevated CO2 disrupts the acid-base balance of internal fluids leading to narcotizing acidosis. Increased acidity decreases the oxygen affinity of hemoglobin and other respiratory pigments (Bohr effect); high CO2 levels CO2 binds directly with respiratory pigments, reducing their capacity to carry oxygen. High CO2 levels also produce metabolic reduction and arrest. Animals that produce CaCO3 skeletons are especially sensitive because CO2 interferes with carbonate biomineralization.
MacLeod and Keller's Cretaceous-Tertiary Mass Extinctions: Biotic and Environmental Changes (1996) provide excellent overviews of the K-T biological record.
About the Author
Along the way, he received four undergraduate Teaching Excellence Awards (1973-1974, 1977, 1980, 1981). His graduate dinoflagellate research program all along the Atlantic Coastal Plain was cited by the American Association of Stratigraphic Palynologists (AASP) as the second most desirable program second only to his mentor, Bill Evitt's, program at Stanford. Two of his graduate students became President of the AASP. He was inducted into the Explorers Club, and Who's Who in Science. In 1977, he was an invited Resource to the World Business Council on the program with some Senators, and Bertram Lance, who was Director of the Office of Management and Budget under President James Carter. At Lance's suggestion, he submitted a letter and a research report on how climate change might affect our civilization directly to President Carter. In 1987, he was an invited speaker to the NASA Langley Research Center on its Colloquium Lectures series which had included scientists such as Werner von Braun and Carl Sagan, where he presented his research on a warming-mammalian embryo death coupling that makes a modern greenhouse exceedingly dangerous to our civilization. His talk was filmed and wound up in the U.S. Senate which invited him to testify at a Senate Hearing on his research on how a modern greenhouse climate change might damage our civilization; he was on the same panel with Sherwood Roland who later won the Nobel Prize. His testimony was published in the Global Environmental Protection Act of 1988. As an invited speaker at the 1989 United Nations International Climate Change meeting held in Cairo, Egypt, his research on how a modern greenhouse might trigger population collapse among mammalian populations was incorporated into the United Nations protocols on coping with climate change.
In 1978, he published the first research indicating that greenhouse climatic warming can trigger global mass biological extinctions (Science, 1978). In 1979, he began linking the global mass extinction at the Cretaceous-Tertiary (K-T) boundary with the Deccan Traps mantle plume flood basalt volcanism in India, and created the Deccan Traps volcanism K-T extinction theory. This brought him into conflict with the Berkeley team spearheaded by the Nobel Laureate, Luis Alvarez, that was simultaneously developing the theory that an extraterrestrial impact event had triggered the extinctions. The scientific debate on whether asteroid impact or Deccan Traps volcanism triggered the K-T extinctions, which is now one of the great debates in the history of science, originated at the 1981 K-TEC II meeting in Ottawa, Canada, where he first debated the Alvarez team.
He retired from his faculty position in 1995. He is now completing a book on the K-T extinctions debate.
E-mail address: [email protected]
Copyright © 1995 Dewey M. McLean