The shrinking earth….continued.
(Quote) : “It started as a discussion in 1983 between two experimental physicists, Richard Muller and Luis Alvarez, regarding a paper they had received. The paper came from David Raup and John Sepkoski, two respected paleontologists, and they were making the remarkable claim that great catastrophes occur on the Earth every 26 million years, like clockwork. It was only 4 years earlier in 1979 that Alvarez had proposed that the extinction of the dinosaurs had been triggered 65 million years ago by an asteroid crashing into the Earth. Many paleontologists had initially paid no regard to this theory, and one had publicly dismissed Alvarez as a 'nut', regardless of his Nobel Prize in physics. But David Raup and John Sepkoski had both liked Alvarez's asteroid theory and now were sending their own theory to Alvarez, or rather their findings, as they offered no explanation. Muller and Alvarez agreed to research their bizarre claim that great catastrophes occur on the Earth every 26 million years.
Raup and Sepkoski had collected a vast amount of data on family extinctions in the oceans, far more than had previously been assembled, and their analysis showed that there were intense periods of extinctions every 26 million years. It wasn't surprising that there should be extinctions this often, but it was surprising that they should be so regularly spaced. Alvarez's work had already shown that at least two of these extinctions were caused by asteroid impacts, the one that killed the dinosaurs at the end of the Cretaceous period, 65 million years ago, and one that killed many land mammals at the end of the Eocene, 35-39 million years ago. But these new findings beggared belief, what could be the cause of such regular events? Was it credible that an asteroid would hit the Earth every 26 million years? An asteroid passing close to the sun has only slightly better than one chance in a billion of hitting our planet. The impacts that do occur should be randomly spaced. not hitting us a precise intervals of every 26 million years. What could make them hit on such a regular schedule? It was ludicrous, but physicists have a wry saying: "If it happens, then it must be possible."
Muller replotted the data using the conventions of physicists rather than paleontologists, giving each extinction an uncertainty in age as well as in intensity. He then placed arrows at regular 26 million year intervals. Eight of them pointed right at the extinction peaks, only two missed. The new chart was more impressive than Muller had expected.
The figures looked impressive, there WERE mass extinctions every 26 million years, two of them were known to be caused as a result of asteroid impacts, but could they ALL be? What could cause it? What model could they come up with to explain it?
Alvarez challenged Muller to come up with a model, and Muller duly obliged: "Suppose there is a companion star that orbits the sun. Every 26 million years it comes close to the Earth and does something, I'm not sure what, but it makes asteroids hit the Earth. Maybe it brings the asteroids with it." Alvarez agreed it was possible, and they carried out calculations to see if the orbit of a companion star was possible without being so big that it would be carried away by the gravity of other nearby stars. The major diameter of an elliptical orbit is the period of the orbit, in this case 26 million years, raised to the 2/3 power, and multiplied by two. Muller quickly showed this to be about 2.8 light years. That put the companion star close enough to the sun so it would not get pulled away by other stars. Alvarez agreed, the model was holding up. The hypothetical star was named "Nemesis". It was proposed that Nemesis, in passing through the Oort cloud, (a comet belt that orbits the outer reaches of the solar system) would perturb the orbit of some of the comets and send them towards the inner parts of the solar system and towards our planet. It is believed to be a dark star, a large mass, much larger than a planet, but not large enough to form a bright star, probably a red or brown dwarf,
Nemesis has not yet been discovered, if it exists it is currently as lost as a needle in a hay stack. among a million brighter stars. If we knew which one it was we could see it through binoculars. With a small telescope its distance from the sun could easily be measured , once we knew where it was.
What do we know for sure? We know that an extraterrestrial object, either a comet or an asteroid, hit the Earth 65 million years ago and brought to an end the great Cretaceous period of the dinosaurs. Other than that we believe that the Earth is subject to periodic storms of comets and asteroids. The important discovery of periodic mass extinctions by Dave Raup and John Sepkoski lies on firm and careful analysis of the data. The periodic extinctions, and the periodic cratering that goes along with them, appear firmly established. The Nemesis theory is consistent with everything we know about physics, astronomy, geology, and paleontology. But it is circumstantial and requires verification. We need to find Nemesis.
When Walter Alvarez became interested in "an inconspicuous layer of clay in the Apennines." Luis Alvarez had suggested that trace analysis of iridium could be used to measure sedimentation rate, but to everyone's surprise it demonstrated that an extraterrestrial impact had taken place. The clay layer was found worldwide, and analysis showed it was about 10% asteroid or comet material, the rest coming from the vaporized rock thrown up by the impact. Five mass extinctions are now known to have iridium signals. The studies of the effects on climate of dust thrown into the air by the impacts led to the discovery of the nuclear winter. The connection between mass extinctions and nuclear winters was made when Edward Anders found soot in the boundary clay layer suggesting that vast firestorms had been set by the impact. The attempts of Raup and Sepkoski to show that mass extinctions occur frequently led them to a surprising, and at first totally inexplicable, conclusion: that mass extinctions take place on a nearly regular 26 -30 million year schedule. Based on this discovery Muller, Marc Davis, and Piet Hut, proposed Nemesis, a companion star to the sun that triggers comet storms, a theory simultaneously proposed by David Whitmire and Albert Jackson. The theory immediately led Muller and Alvarez to the discovery that impacts on the Earth follow the same schedule as the mass extinctions, a correlation found independently by Michael Rampino and Richard Stothers. The concept of storms of comets proved to be more general, and testable, than the Nemesis theory itself, and led to the discovery that the mass extinctions were punctuated during the several million years of their duration. A belief in the comet storms led Donald Morris and Muller to a method of explaining some of the geomagnetic reversal. All this from "an inconspicuous layer of clay in the Apennines." (End quote)
So lets see, a cataclysmic extinction event that takes place every 26 million years caused by a heavenly object impacting the earth.
Nemesis has still not been found even with the help of Hubble and recent deep space probes. Perhaps it was never there in the first place. Perhaps what Alvarez and others like him believe are impact craters, are in fact the remains of gigantic seismic events.A layer of clay containing Iridium does not prove that an asteroid or comet hit the earth as Iridium can be emitted by volcanic action.
The above has been lifted from Keith Mayes’ site, “theories with problems”
“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”
And the Deccan Traps eruption did not take place as an isolated incident. Numerous other volcanic eruptions were taking place at the same time all over the world.
Here follows the article in full:
The Deccan Traps Volcanism-Greenhouse Dinosaur Extinction Theory
A mass extinction involves the relatively rapid elimination (in a geological sense) of many diverse types of organisms on a global scale. The causes of mass extinctions are one of the hottest topics in science today, and have attracted the attention of researchers from many branches of science.
Today, we live in the geological Phanerozoic Eon. The Geologic Time Scale shows that the Phanerozoic is divided into three eras. These are 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 the mass extinctions. On a finer scale, it defines the boundary between the Permian and Triassic periods. The mass extinction that defines the boundary between the Mesozoic and Cenozoic is the best known, primarily because the dinosaurs became extinct at that time. On a finer scale, it defines the boundary between the Cretaceous and Tertiary periods. This website focusses upon the latter event.
Sixty-five million years ago, some phenomenon triggered mass extinctions on the lands and in the oceans so profound that they define the geological boundary between the older Mesozoic Era, often called the "Age of Reptiles," and the modern Cenozoic Era, the "Age of Mammals." On a finer scale, the extinctions define the boundary between the Cretaceous (geological symbol, "K"), and Tertiary ("T") periods. This mass extinction is usually referred to as the K-T extinctions.
The cause of the K-T extinctions is one of the great mysteries in science, and scientists have proposed many kinds of theories to account for it. They range from asteroid or comet impacts, volcanism, sea level changes, supernova explosions, and on and on. Beginning in the 1980s, two theories became the topic of intense scientific debate. These are: (1) the K-T impact extinction theory originated by the Nobel physicist, Luis Alvarez, and his team, and (2) the K-T Deccan Traps volcanism-induced carbon cycle perturbation extinction theory originated by the author which, for short, I call the volcano-greenhouse theory.
In May 1981, I met, and debated, Luis Alvarez and his Berkeley impact team at the K-TEC II (Cretaceous-Tertiary Environmental Change) meeting in Ottawa, Canada. The K-TEC II meeting marks the origin of the K-T impact versus volcanism K-T extinctions debate.
Today, after more than 20 years of often rancorous public debate, and intense efforts by scientists who have collected a huge geobiological data base, neither theory has emerged as victorious. The world of the K-T mass extinctions is so distant in time, vast, and complex, that cause of the extinctions remains controversial. For now, each theory remains but a theoretical framework for future research.
However, much good has come out of the debate. Asteroids and comets have struck earth in the geological past, and some scientists argue that the impacts have triggered mass extinctions. For a species with a short history—that might like to have a long one—we must learn how to protect our civilization from future impacts. And, increasingly, scientists are presenting information showing that other mass extinctions, such as the Permo-Triassic extinctions, the greatest in earth history, coincided with the Siberian Traps flood basalt volcanism.
I will discuss briefly the impact versus volcanism K-T extinctions debate, but will devote this website mostly to the Deccan Traps coupling to the K-T mass extinctions.
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.
Effects of a Major Carbon Cycle Perturbation
Major carbon cycle perturbations affect nearly every aspect of earth's surficial systems, and in often drastic ways. As carbon dioxide builds up in the atmosphere, causing greenhouse climatic warming, climate zones shift causing tropical conditions to migrate over temperate zones. These shifts in climate zones trigger great ecological instability, migrations of animal and plant populations, expand the range of tropical diseases to plague temperate-adapted organisms, and cause them to experience elevated body temperatures, a condition known as hyperthermia, beyond their experiences.
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. Based on my studies of the impact of greenhouse warming upon life, I believe that a major perturbations of the carbon cycle can trigger transitions in the biosphere from order into chaos, and are the most dangerous phenomenon that life can experience.
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 mammals—including humans—are 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).
Welcome to the my Earth Systems and Biosphere Evolution studies.
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 65 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, 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 Volcano–Greenhouse 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 65 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 bioshpere: 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 ofwhich 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 relatioship 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 65 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 Peistocene 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 Volcano–Greenhouse Theory
Sixty-five million years ago, right at K-T boundary time, and coinciding with major shifts in the oxygen and carbon stable isotope records, and the K-T extinctions, the vast bulk of the Deccan Traps lavas erupted onto earth's surface (Basu et al., 1993). One of the greatest episodes of volcanism in earth history, it flooded over a million square miles of India and surrounding areas with layer upon layer of basaltic lava flows, one over the other, forming a lava pile that today, after 65 million years of erosion, is still about one and one-half miles thick in western India, near Bombay. The duration of the eruptions was coeval with major shifts in the carbon and oxygen stable isotope records, "Strangelove conditions" in the oceans, and the K-T mass extinctions. 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).
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 bouyant 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 enlaged 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 Mauritus, 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. 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 65 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 65 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 65 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 bioshpere. 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 dinosaurs—in the strict sense—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.
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 65 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
The author is a Professor Emeritus of Geology in the Department of Geological Sciences, Virginia Polytechnic Institute, Blacksburg, VA, 24061. He has the Ph. D. in geology from Stanford University, and all course work for the Ph. D. in biology. His teaching specialties were: Paleontology, Paleobotany, Palynology, Stratigraphic Palynology, Historical Geology, and Earth Systems and Biosphere Evolution. Since 1969, he directed a Cretaceous-Tertiary marine phytoplankton graduate program. A decade ago, he subsumed it into an Earth Systems and Biosphere Evolution Studies program. His primary interests involve a multidisciplinary, integrative, search for principles and laws of nature concerning the driving sources of the evolution of earth's biosphere through time. In the 1970s, he began laying foundations for a new field of science showing that variations in earth's greenhouse climate caused by variations in the amount of CO2 released onto earth's surface via variations in: (1) mantle degassing from the interior of the earth, and (2) orbital dynamics (Milankovitch cycles) exert control upon mammalian, bird, and reptilian reproductive physiology, and thus population dynamics, and bioevolution, and extinctions. In 1994, he proposed a law of nature linking greenhouse climate change associated with mantle plume volcanism, impacts, and Milankovitch cycles to bioevolution and extinctions (McLean, 1994).
E-mail address: email@example.com
Copyright © 1995 Dewey M. McLean
I hate to mention my shrinking earth theory again but…..is our world subject to an occasional cataclysmic seismic event that not only reshapes the surface, changes all life on its surface but also reduces in size?
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shrinking earth.Two opposing theories.
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