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The Deccan Traps Volcanism-Greenhouse Dinosaur Extinction Theory
Dewey McLean
Introduction
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 victorous. 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.
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.
(fonte: immagini e articolo intero-->Dinosaur Volcano ). -
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Dinosaur Extinction Theory |
