Earth System Geophysics

Steven R. Dickman, Binghamton University, USA

Preface 

Acknowledgments 

About the Companion Website 

Part I An Earth System Science Framework   

1. The Birth of the Earth   

1.0 Motivation

1.1 The Formation of the Solar System

1.1.1 Overview: Contrasting Theories versus Solar System Basics

1.1.2 A Monistic Description of Solar System Formation

1.2 Properties of the Solar System

1.2.1 The Spacing of the Planetary Orbits

1.2.2 Moment of Inertia: A Diagnostic Tool for Planetary Interiors 

1.2.3 A Brief Description of the Properties of Planets and Moons 

1.3 Life in the Solar System, and Beyond

1.3.1 The Search for Planets

1.3.2 Evidence for Life in the Universe 

1.3.3 Evidence for Life in our Solar System 

2. The Evolution of Earth’s Atmosphere 

2.0 Motivation

2.1 The Differentiation of the Earth

2.1.1 A Core by Condensation?

2.1.2 An Act of Differentiation Created the Core 

2.1.3 Consequences of Core Formation 

2.2 The Faint Young Sun

2.2.1 The Young Sun’s Changing Luminosity was Inevitable

2.2.2 A Paradox, and its Resolution

2.2.3 The Urey Cycle 

2.3 Constraints on the Evolution of Atmospheric CO2

2.3.1 Levels of CO2 were (Relatively) Low during Ice House Climates

2.3.2 Other Approaches, and a Synthesis 

2.4 The Development of an Oxygen Atmosphere 

2.4.1 A Mostly Geology-based Chronology of the Rise of Oxygen on Earth 

2.4.2 Oxygen and Evolution: An Overview

2.4.3 Oxygen Chronology: A Synthesis 

3. The Climate System and the Future of Earth’s Atmosphere 

3.0 Motivation

The Climate System

3.1 The Circulation of the Atmosphere

3.1.1 The Sun is the Ultimate Driving Force

3.1.2 Basic Concepts Underlying Atmospheric Circulation

3.1.3 Global Atmospheric Circulation on a Non-Rotating Earth

3.1.4 Global Atmospheric Circulation on the Rotating Earth

3.1.5 Complications of the Three-Cell Model

3.1.6 Implications of the Three-Cell Model for Climate and Regional Circulation

3.1.7 A Jovian Perspective, Briefly

3.1.8 Jet Streams in the Atmosphere

3.1.9 Hurricanes 

3.2 The Circulation of the Oceans

3.2.1 Thermohaline Convection

3.2.2 Wind-driven Circulation

3.2.3 The Wind-driven Oceans Move Heat, Too 

3.3 El Niño and the Southern Oscillation: a coupled atmosphere – ocean phenomenon

3.3.1 El Niño

3.3.2 Southern Oscillation

3.3.3 The Mechanism of a Strong ENSO Event

3.3.4 The Mechanism of a Weak ENSO Event

3.3.5 The Return to Normalcy

3.3.6 There’s an even Bigger Picture 

The Immediate Future of our Atmosphere

3.4 Preliminary Comments

3.5 Solar Variability on Human Time Scales

3.5.1 Sunspot Cycles 

3.5.2 A Connection between Sunspots and a Dramatic Change in Earth’s Climate?

3.5.3 A Few Final Comments on Sunspots 

3.6 Anthropogenic Variations in Climate by the Emission of Greenhouse Gases

3.6.1 Increases in Greenhouse Gas Abundances

3.6.2 Direct and Indirect Impacts on Climate Expected from an Increase in Greenhouse Gas Abundances 

3.6.3 Tempered Expectations: Complications in how these consequences play out 

3.6.4 Anthropogenic Variations in Climate: Evidence concerning direct consequences (– if you insist)

3.6.5 Anthropogenic Variations in Climate: Evidence concerning indirect consequences 

3.6.6 Anthropogenic Climate Change: Some final thoughts 

3.7 A Geophysical Perspective: the rest of this textbook

Part II A Planet Driven by Convection   

4. Basics of Gravity and the Shape of the Earth   

4.0 Motivation

4.1 The Nature of Gravity

4.1.1 Simple Expressions of the Law of Gravitation 

4.2 Newton’s Second Law and the Gravity Field

4.2.1 Cause and Effect, Mass and Weight

4.2.2 Earth’s Gravity Field, and the Answer to a Really Fundamental Question 

4.2.3 Weighing the Earth 

4.3 The Gravity Field of a Three-Dimensional Earth

4.3.1 A Guiding Principle

4.3.2 More Consequences of Gravity Being an Inverse-Square Law Force

4.3.3 Revisiting Newton’s Law of Gravitation, with Superposition 

4.4 The Shape of the Earth, and Variations of Gravity with Latitude

4.4.1 A Motivation to get Complicated

4.4.2 The Earth is not Spherical

4.4.3 Earth’s Rotation is the Cause

4.4.4 A Thorough Description of Centrifugal Force

4.4.5 Gravity versus Centrifugal Force on a Rotating Earth

4.4.6 Indirect Effects of Centrifugal Force on Gravity, and the Idealized Earth 

4.5 Kepler’s Laws

5. Gravity and Isostasy in the Earth System   

5.0 Motivation

5.1 Exploring the Earth System with Gravity

5.1.1 Scaling Down for Gravity Exploration

5.1.2 The Reduction of Gravity Data 

5.1.3 An Application to the Earth System

5.1.4 Gravity Data Measured on a Moving Platform 

5.2 Isostasy and the Earth System

5.2.1 Bouguer’s Discovery and the Principle of Isostasy

5.2.2 Mechanisms to Achieve Isostatic Balance

5.2.3 The Moho and Other Evidence of Airy Isostasy

5.2.4 Airy Isostasy and the Oceanic Response to Atmospheric Pressure Fluctuations 

5.2.5 A Third Mechanism for Achieving Isostatic Compensation 

5.2.6 Isostatic Response to Surface Loads in the Earth System: Anomalous Regions 

5.2.7 Isostatic Response to Surface Loads: Implications for Mantle Rheology 

5.2.8 Global Constraints on Mantle Viscosity 

6. Orbital Perspectives on Gravity 

6.0 Motivation

6.1 Tides

6.1.1 Ebbs and Flows

6.1.2 Tidal Forces

6.1.3 The Response of the Oceans to Tidal Forces

6.1.4 The Response of the Solid Earth to Tidal Forces 

6.2 Precession of the Equinoxes and Orbital Effects on Climate

6.2.1 Precession 

6.2.2 Precession, the Core, and the Geomagnetic Field of the Earth

6.2.3 Precession Can Affect the Earth’s Climate 

6.2.4 Milankovitch and Mars 

6.3 Satellite Geodesy

6.3.1 Satellite Orbital Precession 

6.3.2 The Geoid and Satellite Altimetry 

6.3.3 Geoid versus Spheroid, and Geoidal Heights

6.3.4 More Perspectives on Global Gravity and the Global Geoid 

6.4 Tidal Friction

6.4.1 Another Way of Looking at Tides

6.4.2 The Solid Earth will End Up in the Middle of It All, and Suffer Greatly

6.4.3 Tidal Friction Also Affects the Moon’s Orbit

6.4.4 Tidal Friction has Consequences for the Earth System

6.4.5 Tidal Friction without Oceans, and Astronomical Implications

6.4.6 Theories of the Origin of the Moon 

7. Basics of Seismology  

7.0 Motivation

7.1 Stress and Strain

7.1.1 Stress

7.1.2 Stress: a Rigorous Description

7.1.3 Strain

7.1.4 Strain: a Rigorous Description 

7.2 Relations between Stress and Strain in Elastic and Non-elastic Materials

7.2.1 Ideal Models of Different Materials

7.2.2 Material Properties of an Elastic Medium: Elastic Parameters 

7.3 Elastic Waves

7.3.1 Descriptions of Waves

7.3.2 Elastic Waves: the Wave Equation

7.3.3 Elastic Waves: Reflection and Refraction 

7.4 Surface Waves and Free Oscillations

7.4.1 Surface Waves

7.4.2 Free Oscillations 

7.5 Seismic Waves and Exploration of the Shallow Earth

7.5.1 Refraction Surveys; or, First Arrivals on a Flat Earth

7.5.2 Refraction Surveys: an Illustration with Possible Hydrogeological Implications

7.5.3 Refraction Surveys: Thoughts about Multilayered Situations 

7.6 Seismic Waves and Exploration of the Whole Earth: Preliminaries

7.6.1 Travel Times: Lateral Homogeneity within the Earth

7.6.2 Travel Times: Locating Earthquakes

7.6.3 Travel Times: Identifying Phases on a Seismogram

8. Seismology and the Interior of the Earth 

8.0 Motivation

8.1 Seismology and the Dynamic Earth

8.1.1 Defining Plate Tectonics

8.1.2 Quantifying Plate Motions

8.1.3 Plate Motions through the Ages

8.1.4 A Last Look at Plates and Plate Motions

8.1.5 Travel Times and the Interior of the Earth 

8.2 Seismology and the Large-Scale Structure of the Earth

8.2.1 Travel Times: the Shadow Zone and the Core

8.2.2 Travel Times: Determining Seismic Velocities within the Earth 

8.3 Seismic Velocities and the State of Earth’s Interior

8.3.1 Birch’s Rule 

8.3.2 The Adams-Williamson Equations 

8.3.3 Seismic Tomography 

8.4 Using Earth Models to Learn About the Composition of the Interior

8.4.1 Equations of State

8.4.2 High-Pressure Experiments 

9. Heat from Earth’s Interior 

9.0 Motivation

9.1 Measuring Heat Flow

9.1.1 Basic Ideas and Practical Challenges

9.1.2 Heat Flow Data

9.1.3 Strengthening our Theoretical Foundation of Heat Flow: an Introduction to Del 

9.2 Heat Sources

9.2.1 Radioactivity

9.2.2 Gravitational Energy, Part One

9.2.3 Heat of Compression

9.2.4 Gravitational Energy, Part Two

9.2.5 Moon-forming Impact

9.2.6 Tidal Friction

9.2.7 Another Look at Radioactivity

9.2.8 Growth of the Inner Core

9.2.9 Some Reflections, and What Must Come Next 

9.3 Transmission of Heat in Solids

9.3.1 Conduction Plus Conservation Equals Diffusion 

9.3.2 The Nature of Diffusion

9.3.3 Some Solutions to the Diffusion Equation

9.3.4 Learning from Failure: a Deeper Look into Heat Flow by Conduction

9.4 Transmission of Heat in Fluids

9.4.1 Fluid Stability

9.4.2 How Convection Works in a Fluid

9.4.3 Heat Transmission in a Convecting Fluid

9.4.4 Horizontal Convection

9.4.5 Temperatures within a Convecting Fluid; Fluid versus Solid-State Convection 

9.5 More on Surface Heat Flow in the Earth System

9.5.1 Geothermal Heat and the Thermohaline Circulation 

9.5.2 Subsurface Temperature Variations and Climate Change

10. Geomagnetism and the Dynamics of the Core   

10.0 Motivation

10.1 The Earth’s Magnetic Field

10.1.1 Dipole Fields

10.1.2 An ‘Elemental’ Description of Magnetic Fields, with Reference to the Earth

10.1.3 Magnetic Fields: An Overview of the Earth System 

10.2 Global Descriptions of the Internal Field

10.2.1 Satellite Missions Dedicated to Observing Earth’s Magnetic Fields

10.2.2 Spherical Harmonics, Once Again 

10.2.3 Back to the Surface: A Closer Look at the Crustal (and Geomagnetic) Fields

10.3 Snapshots in Time of the Geomagnetic Field

10.3.1 Current and Recent Snapshots 

10.3.2 Snapshots Further Back in Time 

10.4 Generation of the Geomagnetic Field

10.4.1 Preliminary Assessments 

10.4.2 Fields Weaken, Fields Strengthen

10.4.3 Examples of Simple Dynamos

10.4.4 Inescapable Wisdom from Unavoidable Equations

10.4.5 Dynamo Flow in a Taylor-Proudman World

10.4.6 Some Final Thoughts

References

Index