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 Science 11 explores the fundamental processes that have shaped and continue to shape the Earth and environment in which we live. The physical processes causing earthquakes, volcanic eruptions, tsunamis, windstorms, floods, landslides, meteorite impacts, 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.

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 15 billion years ago or the ensuing history of star supernovas that created the heavy materials 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 eventual 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 produce 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 [Charles Lyell 1797-1875, author of Principles of Geology, 1830]. 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 times yield substantial results

d) Uniformity of Conditions: (non-directionalism) There is no progress in the system, it is in equilibrium.

*"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.

Modern Earth Science 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.

Later in 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 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?

Lastly we 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.

"SCIENCE, in its most fundamental definition, is a fruitful mode of inquiry, not a list of enticing conclusions. The conclusions are the consequence, not the essence."

-- Stephen Jay Gould, The Flamingo's Smile

The underlying theme of this section is the evolution of scientific methodology for addressing questions about the Earth around us, and the nature of processes both routine and catastrophic in our environment. We'll proceed from the ridiculous to the sublime, asking questions that have puzzled humankind from the earliest moments of leisurely circumspection. Let's begin with looking at a rock.....

A chunk of rocky material, comprised of bluish Fluorite crystals is our starting point. From the earliest exploitation of the materials in the environment, humans have explored the physical properties of rocks and other natural substances. Initially this was prompted by the practical necessity of tool and weapon making. As civilization advanced, the consideration of the fundamental essence of our surroundings also deepened. By the time of the Greek civilization, continual scraping for subsistence had subsided, and leisure time allowed intellectual pursuit of fundamental questions: what is a rock, why do they differ, and why are rocky substances different from human tissue, plants, or other living organisms?

The Greek intellectuals began to organize the mode of human inquiry, bringing in the notion of experimentation and hypothesis testing of a formal type. Practical observation led them to adopt the notion that solid, inanimate material was comprised of atoms, tiny building blocks of all materials. For rocks, these atoms are organized in regular structures, yielding crystals, that in turn comprise distinct mineral forms. Regular ordering of the atoms in crystal lattices is controlled by fundamental properties of the atoms, and their ability to interact with one another. While the Greeks lacked any analytic tools capable of probing the details of atomic structure, their systematic thought processes led them in the correct direction. This birth of Scientific Method was short-lived, and unfortunately disciplined human inquiry lapsed into conflict with theological dogma over the next 1500 years, and little more was learned for a long time about the nature of a rock.

Similar consideration of materials that grow and change, such as a toenail, led to a recognition that tiny atoms also comprise the materials of animate objects, but the atoms are organized differently, into molecules that are organized structures, but do not have the lattice structures characterizing rocky materials. The Greeks also made the association that life forms were deriving their subsistence from the environment around them, consuming other life forms, some of which seemed to derive their very essence from the rocks and soils in which they grew. This led to the appreciation that human organisms are very much a product of their environment, indeed evolutionary theory now sees us as having evolved in a manner so as to optimize our utilization of our environment (for example our eyes are tuned to be most sensitive to the peak in the spectrum of solar radiation). As inquiry broadened into a more profound consideration of what are human organisms, there was some tension between the recognition that we were in some way a product in harmony with our environment and the philosophical perception that we are so special that divine explanations must be invoked. Again, the advance of scientific approaches to the nature of living organisms was impeded for many centuries by theological dogma.

With the flourishing of knowledge that followed the upheavals of the Renaissance and the onset of the Industrial Age, scientific method was reinvigorated and greatly expanded as an intellectual mode of inquiry. The ability to experiment and measure advanced rapidly with a proliferation of discoveries and technical innovations. Fields of science emerged, such as chemistry and physics, followed by applied fields such as geology. Scientists developed many new ways to determine compositions of minerals and molecules, adding depth to the fundamental understanding of matter. Chemistry and physics systematically identified the distinctive atomic materials, charting out the Periodic Table of the Elements. Tools such as mass spectrometers, which are able to take tiny samples of materials and break them apart to measure the relative abundance of their constituent atoms. Such machines are now widely used. Another critical tool was spectroscopy, the analysis of radiation emitted by an object when it is heated. The light given off is generated by the excitation states of the constant atoms in the material, which imparts a distinctive 'color' to the light. By using methods of chemistry and physics, mass spectrometers, and spectroscopic sensors, humans began to count and measure the materials in our environment...

Let's up the scale a bit, and now ask a question germane to this class: What is the Earth and what is it made of? This was an issue also probed by the early Greeks, who came to the recognition that the Earth is a rocky planet with fluid envelopes in the oceans and atmospheres. They also recognized that descending deep into mines led to hotter conditions, and combined with the outpourings of magma during volcanic eruptions, it was decided that the planet was hotter in its interior. Even after the ups and downs of the Dark Ages and the Scientific revolution, geologists have been confronted with the question even up to today. Given that the deepest drill hole ever achieved is a scant 10 km deep, out of the 6371 km radius of the Earth, and that even the deepest rocks brought up to the surface in volcanic eruptions appear to have originated no deeper than a few hundred kilometers, how can we answer this question?

In part, the answer comes from looking outside the Earth rather than into its unreachable depths. This is one of the most important attributes of scientific method, the sometimes unexpected directions to solution of a problem that emerge from rethinking the problem logically. The approach is as follows: to understand the Earth, we must understand the system in which it evolved. Initially, this led us to consider the Earth as part of the Solar System, and then the Solar System as part of the Milky Way Galaxy, and the Milky Way as part of the Universe. Each expanding perspective probes more deeply into the question of what is the Earth, and ultimately what are we humans, which are products of the Earth itself.

The Greeks again were on the right track, viewing the Earth as one of the planets orbiting the Sun. The Heliocentric notion of a solar system was born with Pythagoras (580-500B.C.), but languished through the Dark Ages as theological perspectives placed the Earth in the center of the Cosmos. Copernicus (1473-1543 A.D.) and Kepler (1571-1630 A.D.) drew upon new tools such as the telescope and systematic measurements using careful scientific method to establish the correctness of the Heliocentric solar system and the laws of planetary motion. The recognition that the Earth was but one of a system of diverse planetary bodies orbiting a star of vastly greater mass led to a profound enlightenment. Given that stars themselves evolve (a notion made clear by observations of supernova explosions), one secret to understanding what the Earth is made of is to address how it formed when the entire solar system did. Assuming that the Sun and its planets formed together (as strongly suggested by the common rotational plane of the planets - the plane of the ecliptic), it is very reasonable to think that the Earth must have a distribution of rocky materials very similar to that of the Sun, as the primary mass of the solar system resides in the star. To make progress, we must ask: What is the Sun made of?

The composition of the Sun is not readily subject to direct measurement, so once again it is scientific method that leads to a non-obvious solution of this question. A critical development was provided by an eyeglass maker, Frauenhofer, in 1814. He developed the first glass prisms, which refracted white light from the Sun, separating the different wavelengths of radiation. (If we think of each color of light as a propagating light wave, the wavelength is the spatial distance between crests of the wave. For a surfer this would be length between peaks in a set of waves. The period of the wave is the time it takes between the passage of one wave crest and the next past a fixed point. The wavelength, L, is equal to the speed of the wave, c, times the period, T. L=cT. In this case the speed is the speed of light, which is the same for all light in a vacuum.)

Using a prism to separate 'white' sunlight into its separate colors (as happens naturally by air moisture to produce a rainbow), one finds colors ranging from blue to green to yellow to orange to red to violet, but in the colors there are dark lines. The colors represent emissions, and the dark lines represent absorptions of certain wavelengths of light. By doing experiments and theory, scientists established what wavelengths of light are emitted or absorbed by different materials under very hot conditions. From comparing the observed spectrum of the sun, resolved in great detail in the range 3900 to 6000 angstroms, we are able to state with good accuracy the relative abundance of elements in the Sun (!).

Now, even if we accept the notion that the composition of the Sun, inferred by the unexpected method of looking at its light radiation, tells us the primary composition of the entire solar system (since most of the mass of the solar system is in the sun), clearly there are important differences between the Earth and Sun. For example, the Sun's spectrum indicates a great relative abundance of hydrogen (H) and helium (He) relative to, say, Silicon (Si). Silicon is a major component of the (silicate) rocks of the Earth, so there would have to be vast amounts of H and He somewhere in the Earth if our planet had the exact same composition as the Sun, but this cannot be reconciled with measurements of the atmosphere, the ocean, or the mean density of the Earth. Clearly, the Earth has fewer of the light, volatile gasses that the Sun has retained, which makes sense because the Earth's gravity is so much less than that of the Sun that very light gasses easily escape into space, leaving only a modest amount of nitrogen (N) and oxygen (O) on the planet. But, this difference raises the question: if the Earth's size modifies its composition relative to the Sun, what other differences are there? So, we need another estimate of the bulk composition of the solar system, preferably provided by a sample more similar to the rocky Earth.

Well, such samples fall to Earth daily, in the form of meteorites. Such objects are believed to share some common origins with the Earth, forming as small chunks of cool debris from the cloud of gas and dust that the solar system emerged from. But meteorites come in vastly different types, some being pure metal, some extensively melted rock, some rock-metal combinations that have little evidence of melting, and a special class, called Carbonaceous Chondrites, being meteorites that have experienced very little heating, remixing, or melting, and appear to have formed from the most primitive soup of the solar nebula, just as did the Sun. While almost devoid of light gasses like, H, He, O, N, these meteorites have been carefully studied, as they may represent what the ingredients were that went into the Earth 4.5 billion years ago when it formed. Prior melting and mixing of the Earth has undoubtedly redistributed the components internally, but the bulk composition may be very similar to the Carbonaceous Chondrite.

Strong support for this hypothesis comes from comparing the bulk composition of the Sun, inferred from spectroscopy, with that of the bulk composition of the meteorite inferred from mass spectrometry. The correlation is astounding for all materials other than the volatile gasses H, He, O, C, and N. The inference that the same relative abundance of the more refractory heavier elements exists in the Earth as exists in the Sun and the primitive meteorites gives us our best answer as to what is the Earth.

So, we can say now, based on this form of Scientific inference, coupled with other direct observations that we will hear about later, that the Earth is:

A Layered Planet:

Atmosphere has Nitrogen, Oxygen, Neon

Oceans have Water (H2O), Salt, trace elements

Crust (from 6-70 km thick)

Mantle (from below the crust to 2890 km deep)

Core (down to the center of the Earth).

The compositions are:

Crust + Mantle 69% Total Mass

Compound Weight %

SiO2 48%

MgO 34%

FeO 7.9%

Al2O3 5.2%

CaO 4.2%

Core

Compound Weight %

Fe (iron) 89

Ni (nickel) 6

S,O,Si 5

While the process of inference is such that these numbers have some uncertainty, most scientists debate values at the level of 1%, not the bulk numbers at all. Strange, isn't it, that we can come to strong conclusions about material deep in the Earth that we have never directly seen or touched, largely as a result of looking up at the Sun and catching small rocks that tumble from the sky?

Now, having some idea of the bulk composition of the Sun, the Earth, and the Solar System, one can follow up with the obvious question: Is the composition of the Earth unusual relative to the whole Universe? This probes to the heart of the uniqueness of this planet and of the processes leading to its existence. Spectroscopy again supplies much of the answer, as we can look at the radiation from distant stars, even distant galaxies, and infer gross chemical compositions from the absorption/radiation spectra. This leads to an estimate of the Cosmic Abundances of the Elements:

#Atoms/atom of Silicon (Si)

H 27,200 Hydrogen

Ne 3.8 Neon

N 2.5 Nitrogen

Mg 1.1 Magnesium

Si 1.0 Silicon

Fe 0.0008 Iron