Catastrophe: Katos: over, down, very + Strephein: to turn
"A momentus, tragic, usually sudden event marked by effects ranging from extreme misfortune to utter overthrow or ruin": Disaster
Disaster: Dis + Aster: Evil Star
Earth Catastrophes (EART 80A) explores the fundamental processes that have shaped and continue to shape the Earth and environment in which we live. The physical processes causing supernovas, moon formation, meteroite impacts, mass extinctions, earthquakes, volcanic eruptions, tsunamis, windstorms, floods, landslides, ozone hole depletion, global warming and other phenomena will be described, along with the role played by these rapid processes in the geological and biological evolution of Earth. The entire time scale from formation of the Universe to the present and future Earth system will be considered.
Eart 80A is a Physical and Biological Sciences Division Topical Course, satisfying a distribution requirement for a Topical in the Physical and Biological Sciences (T2). It also now satisfies the Q, for quantitative experience. This will be obtained through homework exercises that will use basic mathematics to further explore some of the topics in the lectures. The class will be divided into three parts:
I. Cosmology and Global Catastrophes
II. Internal Earth Processes and Catastrophes
III. External Earth Processes and Catastrophes
Each part will culminate in an in-class quiz addressing only that Part. There is no Final Exam. Each exam will comprise 25% of the course credit. The final 25% will be based on participation in Discussion sections and about 7 weekly homework exercises that will be handed out throughout the term. Several videos will be shown during the term to help illustrate some of the complex notions in the material.
This class will take a broad perspective of catastrophes in the Earth System, striving to introduce you to the field of Earth Sciences via a panorama of Earth phenomena. The first third of the class will establish the long-term history of the planet, from the creation of its elements in either the Big Bang, some 14 billion years ago or the ensuing history of star supernovas that created the heavy materials now comprising the Earth. We will discuss the processes of nucleosynthesis and stellar collapse by which stars build up heavy elements and them disgorge them in cataclysmic explosions for eventually incorporation into the Earth. As the materials cool and collide to build up planetisimals and asteroids, the role of gravity asserts itself in sweeping the debris in a solar nebula into planets orbiting the central star. The Earth assembled rapidly, and near the final stages of its growth it is believed that it was suddenly hit by a Mars-sized 'final' planetisimal, resulting in a splaying off of material that consolidated in orbit to produced the Moon. This last major in-fall led to the Earth's seasons, tides, and a massive melting of the surface. As the Earth subsequently cooled, it began a long course of evolution as a dynamic system, now in its 4.5 billionth year! From an initially inhospitable surface environment, with no atmosphere or oceans, and no life forms, the system has evolved to its present state, benevolent for humans because we evolved in response to the environment existing in this stage of the planet's history. As life sprung up, it pursued a course of evolution involving both gradualism and catastrophism, with changes induced by mutation, environmental adaptation, and punctuated extinction. Much of the class will explore the relative role of gradual processes versus catastrophic processes in shaping Earth's history and the evolution of its life forms.
Earth Sciences has long been influenced by two basic schools of thought:
Uniformitarianism [formulated by James Hutton 1726-1797, author of Theory of the Earth in 1795, John Playfair, who wrote Illustrations of the Huttonian Theory in 1802, and Charles Lyell 1797-1875, author of Principles of Geology from 1830-1833]. This is the notion that the 'present is the key to the past' via several fundamental laws:
a) Uniformity of Law: Natural laws are invariant in space and time*
b) Uniformity of Process: (actualism) Can explain past results as outcome of causes in operation today
c) Uniformity of Rate: (gradualism) Ordinary processes operating over long timesyield substantial results
d) Uniformity of Conditions: (non-directionalism) There is no progress in the system, it is in equilibrium.
Based on the notion of Uniformitarianism, observations of processes in the environment today can be extrapolated back in time to say what took place in the past. The slow etching away of a mountain as it erodes by rainfall, landslide, or subsidence at slow rates in the present suggests that great spans of time are needed for wearing away mountains. That the rocks are themselves comprised of eroded remains of early rocks indicates that there is a 'great geological cycle' of rock deposition in ocean basins, uplift and mountain formation, erosion and deposition, again and again, with, to Hutton, 'no vestige of a beginning, no prospect of an end'. The notion of great age of the Earth required to explain the surface geology ran afoul of theological dogma which invoked a literal interpretation of the bible suggesting an age of the Earth no more than 6000 years.
*"The most incomprehensible thing about the Universe is that it is comprehensible" -- Albert Einstein
Catastrophism [Georges Cuvier 1769-1832]. The doctrine that changes in the Earth have been brought about suddenly, by physical forces operating in ways that cannot be observed today. This line of thought was in part inspired by theological foundations in the myth of the Noahnic Flood, and in the story of genesis itself, but it had the plausible assertion that not all of the processes that have shaped the Earth are observable today. Some geological formations, such as massive piles of basaltic rock are unlike anything being produced by volcanoes today, and one can invoke the notion that past outpourings of lava were simply much vaster than any witnessed in human history. Sudden flash floods are known to excavate moderate size canyons in flat terrain; why not a greater storm of the past as an agent for scouring the Grand Canyon? Fossils of strange life forms are found which bear no resemblance to known animals; why not catastrophic devastations of past life? While some catastrophists strove to conform all geological observations to a biblical time scale (as do modern day 'Creationists'), many were scientifically oriented thinkers, skeptical of the notion that only rates and processes observed today have acted (or will act) in the Earth in the past (and future).
Modern Earth Sciences acknowledges the importance of both Uniformitarianism and Catastrophism. Much of the uniqueness of our human existence is a precarious balance of past catastrophic and gradual events, leading to the current state of the Earth. We will see how these have influenced the long-term evolution of the Earth in Part I.
In Part II of the class we will consider how the present-day state of the internal Earth system drives catastrophic processes such as earthquakes and volcanoes. These are surface manifestations of large-scale motions of the interior and the surface. The key to understanding these phenomena is considering them in the context of how the internal system works, as a large planetary-scale heat engine that is trying to find the most effective way to cool off the planet. The prevailing paradigm of Plate Tectonics will be explained, as this represents the surface manifestation of the overall heat engine in the planet.
Even upon understanding the nature of dynamic Earth catastrophes, we are confronted with the need to make societal decisions regarding mitigation efforts. How much money can/should society invest in reducing the future losses from foreseeable natural disasters? What are the strategies for earthquake and volcanic eruption prediction that may enable us to reduce the effect of such events?
Part III will explore the surface processes shaping the environment in which humans exist, largely involving the heat energy from the sun and the action of gravity. Atmospheric circulation and evolution are of great importance, as the source of storms, for providing protection from radiation, and in controlling the circulation of water and oxygen in the system. We will seek basic understanding of long-term changes in the atmosphere that are responsible for ice ages, global warming, and even the evolution of life. Floods, avalanches, and landslides will be explored as other surface phenomena. The role of human activity in modifying the chemistry of the atmosphere, and the response of the surface to erosion and slope stability will be considered, along with agricultural practices that have resulted in desertification.
Throughout these three parts of the class, each of which culminates in an in-class quiz, we will consider how human inquiry and rationale thought pose, address, and often solve problems related to the Earth system that we live in. While undeniably complex, and many events will never be fully understood due to lack of preservation of information, the scientific consensus is that natural processes account for what has transpired, without the need to captiulate and invoke the 'solution' of Intelligent Design.
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