Exploring our Evolving Planet: An Introduction to Geophysics
Exploring our Evolving Planet: An Introduction to Geophysics
Sep 2030, Wiley-Blackwell
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DescriptionThe book we are proposing will be based on a beginning geophysics course introduced at Northwestern University about 20 years ago that has been evolving since. This course is required of geology majors, and is taken as a distribution course by engineering majors. It provides a relatively rigorous and homework-intensive overview of the structure and evolution of the Earth and terrestrial planets. The course aims to provide students with an intuitive understanding of the physical processes that have shaped our planet, and does this through many interesting examples, analogies and demonstrations. The book we are proposing will do the same: provide students with a clear, exciting and intuition-based presentation of the complex and interconnected structure and evolution of Earth.
The course at Northwestern is a bridge between 100-level (descriptive introduction for non-majors, aka "rocks for jocks", "moons for goons") and 300-level (seismology, plate tectonics, mineral physics, tectonophysics, etc) classes taken by seniors & 1st year grad students. Hence the class is more of an overview (broader but not as deep) than geophysics courses for seniors or first year graduate students like those for which most texts (Fowler, Stacey, etc.) are designed.
The course gets good reviews because its approach seems to serve the three types of students in the class:
1) Geology majors who plan to take higher-level geophysics courses are introduced to a range of concepts that allow them to "see the forest" when they move up to specialized higher-level courses. They learn many basic concepts and vocabulary terms, and, most crucially, understand how the different topics are interrelated.
2) Geology majors who do not plan to take higher-level geophysics courses learn enough about basic concepts to appreciate them. The presentation is such that they can learn concepts at a level beyond the purely descriptive.
3) Engineering majors and students majoring in other sciences, who typically have not had previous earth science classes, get a good introduction to many topics in the earth sciences at a higher level than in a 100-level course. They seem to enjoy the class and do as well as the geology majors.
Because no book was fully suitable, class notes have been developed that will form the basis of the book. In the past few years, the class notes, overheads, homework, and demonstrations/labs have been put on the web (http://www.earth.northwestern.edu/people/seth/202).
An article (EOS, 78, 521-532, 1997) describing the demonstrations, such as having students test partitioning during fractional crystallization with half-frozen apple juice, drew a great deal of interest. A lot of instructors say they like the web site and find it helpful in developing their courses. As such, it seems that there will be a market for a book based on the course.
In the proposed book, concepts like Snell’s law and the heat equation will be derived for simple cases. Topics will be tied to the students' beginning physics, chemistry, and calculus courses because experience has shown that these subjects benefit from reinforcement. We thus discuss Snell’s law in seismology but explore its applications to fiber optics, the rainbow, and tsunami propagation. Similarly, discussion of phase diagrams incorporates freeze-dried food and liquefied natural gas. Students seem to find these connections interesting and helpful.
A basic theme of the book will be “how do we know this?” Hence a variety of data acquisition systems including seismometers, magnetometers, mass spectrometers, X-ray diffraction, diamond anvils, satellite altimeters, GPS, space missions (NEAR, WMAP…), etc., will be discussed briefly with explanatory diagrams.
Another important theme of the course is that our geophysical hypotheses of our planet’s composition and dynamics are continuously evolving and there remains much to be learned. The idea here is to remind students that there are many first-order problems remaining, and that they could still be the ones to make major discoveries about the earth
Chapters will contain both problem sets and boxed demonstrations or examples. The demonstrations are very important for providing the students with a physical, geometrical or visual understanding of many of the complex topics discussed. Some can be done with pencil and paper, such as the plate kinematics labs. For example, one of these involves cutting out a map of western North America along the Pacific-North America boundary and rotating the plate about the Euler pole. Other demonstrations can be done with simple tools, such as the apple juice experiment, simulating radioactive decay with coin flips, or a ball-and-string experiment illustrating conservation of angular momentum.
Similar to the case of Stein & Wysession’s Seismology, there will be a book web site with downloadable figures and (by password for instructors) homework solutions.
Chapter 1: Overview of an evolving planet.
A. Introduction, using 2004 Indian Ocean earthquake and tsunami as an illustration of geophysical processes.
B. An overview of Earth's layered structure.
C. The age and history of the earth.
D. Transfer of heat as "the geological lifeblood of planets.".
E. Earth's unique style of heat transfer: plate tectonics.
F. Significance of plate tectonics for the origin of life and its survival, climate, resource generation and concentration.
G. Natural hazards: "civilization exists by geological consent.".
Demonstrations: finding what’s in a mystery box by different techniques, effects of shaking and liquefaction on structures.
Chapter 2: Shape and size of the earth.
A. Sphere: Earth's size, mass, density as function of radius.
B. Differentiated planet.
C. Rotating Ellipsoid: Ellipticity, moment of inertia of the earth.
D. Three-dimensional variations: Geoid, density anomalies.
E. Magnetic field and magnetosheath..
Demonstrations: measuring acceleration of gravity with pendulum or ball drop, moment of inertia, conservation of angular momentum, pressure..
Chapter 3: Earth structure from seismology.
A. Seismometers and seismograms.
B. Seismic wave propagation.
C. Snell's law.
D. Reflection and refraction.
E. Body and surface waves, normal modes.
F. Deriving layered velocity structures from travel times and waveforms.
G. Structure of crust, mantle, core.
H. Differences between continents and oceans.
I. Implications of three-dimensional variations..
Demonstrations: wave properties - slinky, gong, dominoes, diffraction, etc..
Chapter 4: Composition of the earth.
A. Review of Minerals.
B. Review of Rocks - focus on silicates.
C. Metamorphism and rock deformation.
D. Rock cycle and plate tectonics.
E. Magma composition and viscosity.
F. The causes of melting and the role of water in the rock cycle.
G. Composition of ocean: ocean lithosphere genesis and history.
H. Composition of continents: orogenesis, accretion, creation of granite.
I. Elastic Moduli as functions of P,T,X: mineral stability, phase diagrams.
J. Going deeper: Analogues, equations of state, high-pressure mineral physics.
K. Phase diagrams and mantle velocity discontinuities.
L. Composition of the upper mantle, transition zone, and lower mantle.
M. Composition of the inner and outer core: relation between them.
N. Anisotropy: Texture and Flow.
Demonstrations: fractional crystallization with juice, pressure melting of ice, volcano shapes from viscosity with chocolate syrup & jam.
Chapter 5: Earth as a heat engine.
A. Conductive heat equation, solutions.
C. Radioactivity & heat production.
D. Using radioactivity to determine the age of the earth.
E. Convection, Rayleigh number.
F. Viscosity and rock flow.
G. Core convection and generation of the magnetic field.
H. Convection in the oceans and atmosphere: climate change.
I. Role of thermal boundary layers.
J. Formation of the lithosphere as cold strong boundary layer.
K. Importance of core-mantle boundary on mantle convection.
L. Surface radiation and interaction with the atmosphere..
Demonstrations: convection, age dating with coin flips.
Chapter 6: Plate tectonics.
A. Relation to thermal evolution and convection.
B. Roles of continents and oceans in plate tectonics.
C. Global plate motions and space geodesy (GPS, VLBI, SLR, SAR).
D. Marine magnetic anomalies: age of ocean seafloor.
E. Seafloor topography and satellite gravity.
F. Continental paleomagnetism and early plate motions.
G. Historical geology: formation and history of the continents.
H. Earthquake focal mechanisms and the seismic cycle.
I. The earthquake prediction challenge.
J. Plate boundaries and kinematics (Euler vectors).
K. Mechanics of plate tectonics, thermal evolution of lithosphere, ridges, subduction zones.
L. Plate dynamics: slab pull, ridge push, slab suction.
M. The hotspot/plume controversy.
N. The onset of subduction, break-up of supercontinents, and the Wilson cycle.
O. Plate tectonics and mineral resources..
Demonstrations: paper cutouts for transform faults, Euler vectors, relative and absolute plate motions, inexpensive handheld GPS receiver.
Chapter 7: Earth in the solar system.
A. The Big Bang, baryogenesis, nucleosythesis, galaxies, and the shape of the universe.
B. The life cycle of stars.
C. Determining the age of the Earth.
D. Formation of the Solar System.
E. Meteorites and implications for earth composition.
F. Formation of Earth and the other planets.
G. Inner (terrestrial) versus outer planets.
H. Planets as evolving systems.
I. Different planetary styles of convection.
J. Relation of lithospheric thickness to other planets, role of size (Moon, Mars, Venus).
K. Evolution of atmosphere, relation to plate tectonics, role in surface temperature (greenhouse) and survival (or not) of life.
L. Unresolved issues for other planets.
M. The uniqueness or non-uniqueness of Earth in supporting advanced life..
Demonstrations: surface area/volume effects on cooling rate using ice, Drake equation for extraterrestrial life