Geology For Dummies

Alecia M. Spooner has been teaching at the college level for more than 15 years. She currently teaches at Seattle Central College, where she is Professor of Earth and Environmental Sciences. Alecia teaches earth science courses that are accessible and engaging, while stressing scientific literacy and critical thinking.

Introduction 1

About This Book 1

Foolish Assumptions 2

Icons Used in This Book 2

Beyond the Book 3

Where to Go from Here 3

Part 1: Studying The Earth 5

Chapter 1: Rocks for Jocks (and Everybody Else) 7

Finding Your Inner Scientist 8

Making observations every day 8

Jumping to conclusions 8

Focusing on Rock Formation and Transformation 8

Understanding how rocks form 9

Tumbling through the rock cycle 9

Mapping Continental Movements 10

Unifying geology with plate tectonics theory 10

Debating a mechanism for plate movements 11

Moving Rocks around on Earth’s Surface 11

Interpreting a Long History of Life on Earth 12

Using relative versus absolute dating 12

Witnessing evolution in the fossil record 13

Chapter 2: Observing Earth through a Scientific Lens 15

Realizing That Science Is Not Just for Scientists 15

Using a Methodical Approach: The Scientific Method 16

Sensing something new 17

I have a hypothesis! 18

Testing your hypothesis: Experiments 18

Crunching the numbers 19

Interpreting results 21

Sharing the findings 21

Building New Knowledge: A Scientific Theory 21

It’s never “just a theory” 22

Scientific theory versus scientific law 22

The road to paradigms 23

Speaking in Tongues: Why Geologists Seem to Speak a Separate Language 23

Lamination vs foliation: Similar outcomes from different processes 24

Gabbro vs basalt: Different outcomes from similar processes 24

Chapter 3: From Here to Eternity: The Past, Present, and Future of Geologic Thought 27

Catastrophe Strikes Again and Again 28

Early Thoughts on the Origin of Rocks 28

Developing Modern Geologic Understanding 29

Reading the rock layers: Steno’s stratigraphy 29

These things take time! Hutton’s hypothesis 30

What has been will be: Lyell’s principles 31

Uniformi-what? Understanding the Earth through Uniformitarianism 32

Pulling It All Together: The Theory of Plate Tectonics 32

Forging Ahead into New Frontiers 33

Asking how, where, and why: Mountain building and plate boundaries 33

Mysteries of the past: Snowball earth, first life, and mass extinctions 34

Predicting the future: Earthquakes and climate change 35

Out of this world: Planetary geology and the search for life 37

Chapter 4: Home Sweet Home: Planet Earth 39

Earth’s Spheres 39

Examining Earth’s Geosphere 41

Defining Earth’s layers 41

Examining each layer 43

Part 2: Elements, Minerals, And Rocks 49

Chapter 5: It’s Elemental, My Dear: A Very Basic Chemistry of Elements and Compounds 51

The Smallest Matter: Atoms and Atomic Structure 52

Getting to know the periodic table 53

Interpreting isotopes 56

Charging particles: Ions 56

Chemically Bonding 57

Donating electrons (ionic bonds) 57

Sharing electrons (covalent bonds) 57

Migrating electrons (metallic bonds) 58

Formulating Compounds 60

Chapter 6: Minerals: The Building Blocks of Rocks 61

Meeting Mineral Requirements 62

Making Crystals 62

Identifying Minerals Using Physical Characteristics 63

Observing transparency, color, luster, and streak 63

Measuring mineral strength 64

If it tastes like salt, it must be halite: Noting unique mineral properties 68

Measuring properties in the lab 69

Realizing Most Rocks Are Built from Silicate Minerals 70

Finding silicates in many shapes 71

Grouping silicate minerals 74

Remembering the Nonsilicate Minerals 74

Carbonates 74

Sulfides and sulfates 75

Oxides 75

Native elements 76

Evaporites 76

Gemstones 77

Chapter 7: Recognizing Rocks: Igneous, Sedimentary, and Metamorphic Types 79

Mama Magma: Birthing Igneous Rocks 80

Remembering how magma is made 80

Classifying melt composition 81

Reacting in sequence: Bowen’s reaction series 81

Evolving magmas 83

Crystallizing one way or another: Igneous rocks 84

Classifying igneous rocks 85

Studying volcanic structures 89

Looking below the surface 92

Merging Many Single Grains of Sand: Sedimentary Rocks 94

Weathering rocks into sediments 95

Changing from sediment into rock 98

Sizing up the grains: Classifying sedimentary rocks 99

Searching for sedimentary basins 102

Telling stories of the past: Sedimentary structures 103

Stuck between a Rock and a Hard Place: Metamorphic Rocks 106

Turning up the heat and pressure: Metamorphism 106

Grading metamorphism with index minerals 107

Between the mineral sheets: Foliation, or maybe not 108

Categorizing metamorphic rocks 110

Tumbling through the Rock Cycle: How Rocks Change from One Type to Another 112

Part 3: One Theory To Explain It All: Plate Tectonics 115

Chapter 8: Adding Up the Evidence for Plate Tectonics 117

Drifting Apart: Wegener’s Idea of Continental Drift 118

Continental puzzle solving 118

Fossil matching 119

Stratigraphic stories 120

Icy cold climates of long ago 122

Meeting at the equator 123

Searching for a mechanism 123

Coming Together: How Technology Sheds Light on Plate Tectonics 124

Mapping the seafloor 124

Flip-flopping magnetic poles: Paleomagnetism and seafloor spreading 125

Measuring plate movements 127

Unifying the theory 127

Chapter 9: When Crustal Plates Meet, It’s All Relative 129

Density Is Key 130

Two of a Kind: Continental and Oceanic Crust 131

Dark and dense: Oceanic crust 131

Thick and fluffy: Continental crust 131

Understanding Why Density Matters: Isostasy 132

Defining Plate Boundaries by Their Relative Motion 133

Driving apart: Divergent plate boundaries 134

Crashing together: Convergent plate boundaries 136

Slip-sliding along: Transform plate boundaries 139

Shaping Topography with Plate Movements 141

Deforming the crust at plate boundaries 141

Compressing rocks into folds 142

Faulting in response to stress 144

Building mountains 146

Chapter 10: Who’s Driving This Thing? Mantle Convection and Plate Movement 149

Running in Circles: Models of Mantle Convection 150

Mantle plumes: Just like the lava in your lamp 152

The slab-pull and ridge-push models 152

Using Convection to Explain Magma, Volcanoes, and Underwater Mountains 153

Plate friction: Melting rock beneath the earth’s crust 154

Creating volcanic arcs and hotspots 154

Birthing new seafloor at mid-ocean ridges 158

Shake, Rattle, and Roll: How Plate Movements Cause Earthquakes 158

Responding elastically 159

Sending waves through the earth 160

Measuring magnitude 160

Part 4: Superficially Speaking: About Surface Processes 163

Chapter 11: Gravity Takes Its Toll: Mass Wasting 165

Holding Steady or Falling Down: Friction versus Gravity 166

Focusing on the Materials Involved 167

Loose materials: Resting at the angle of repose 167

Bedrock: Losing its stability 168

Triggering Mass Movements 168

Adding water to the mix 168

Changing the slope angle 169

Shaking things up: Earthquakes 170

Removing vegetation 170

Moving Massive Amounts of Earth, Quickly 171

Falls 171

Slides and slumps 171

Flows 172

A More Subtle Approach: Creep and Soil Flow (Solifluction) 173

Chapter 12: Water: Above and Below Ground 175

Hydrologic Cycling 176

Driving the cycle with evaporation 176

Traveling across a continent 177

Streams: Moving Sediments toward the Ocean 178

Draining the basin 178

Two types of flow 179

Measuring stream characteristics 180

Carrying a heavy load 180

Measuring what is transported 181

Eroding a Stream Channel to Base Level 182

Seeking Equilibrium after Changes in Base Level 183

Leaving Their Mark: How Streams Create Landforms 184

Draining the basin 184

Meandering along 185

Depositing sediments along the way 187

Reaching the sea 187

Flowing beneath Your Feet: Groundwater 188

Infiltrating tiny spaces underground 188

Measuring porosity and permeability 189

Setting the water table 189

Springing from rocks 190

That sinking feeling: Karst, caves, and sinkholes 192

Chapter 13: Flowing Slowly toward the Sea: Glaciers 195

Identifying Three Types of Glaciers 196

Understanding Ice as a Geologic Force 196

Transforming snow into ice 197

Balancing the glacial budget 197

Flowing solidly down the mountain 198

Eroding at a Snail’s Pace: Landforms Created by Glacial Erosion 199

Plucking and abrading along the way 200

Creating their own valleys 200

Speaking French: Cirques, arêtes, et roche moutonnées 201

Leaving It All Behind: Glacial Deposits 203

Depositing the till 203

Plains, trains, eskers, and kames 204

Behaving erratically: Large boulders in odd places 206

Where Have All the Glaciers Gone? 206

Filling the erosional gaps 206

Cycling through ice ages 207

Rebounding isostatically 209

Chapter 14: Blowing in the Wind: Moving Sediments without Water 211

Lacking Water: Arid Regions of the Earth 212

Transporting Particles by Air 212

Skipping right along: Bed load and saltation 213

Suspending particles in air 214

Deflating and Abrading: Features of Wind Erosion 214

Removing sediments 215

Scratching the surface 215

Just Add Wind: Dunes and Other Depositional Wind Features 216

Migrating piles of sand: Dunes 217

Shaping sand 218

Laying down layers of loess 219

Paving the Desert: Deposition or Erosion? 221

Chapter 15: Catch a Wave: The Evolution of Shorelines 223

Breaking Free: Waves and Wave Motion 223

Dissecting wave anatomy 223

Starting to roll 224

Going with the flow: Currents and tides 226

Shaping Shorelines 228

Carving cliffs and other features 228

Budgeting to build sandbars 228

Categorizing Coastlines 230

Part 5: Long, Long Ago In This Galaxy Right Here 233

Chapter 16: Getting a Grip on Geologic Time 235

The Layer Cake of Time: Stratigraphy and Relative Dating 236

Speaking relatively 236

Sorting out the strata 236

Putting rock layers in the right order 237

Losing time in the layers 238

Show Me the Numbers: Methods of Absolute Dating 240

Measuring radioactive decay 241

Common radioactive isotopes for geological dating 244

Other exacting methods of geological dating 245

Relatively Absolute: Combining Methods for the Best Results 248

Eons, Eras, and Epochs (Oh My!): Structuring the Geologic Timescale 249

Chapter 17: A Record of Life in the Rocks 253

Explaining Change, Not Origins: The Theory of Evolution 254

The Evolution of a Theory 254

Acquiring traits doesn’t do it 254

Naturally, selecting for survival 255

Mendel’s peas please 255

Genetic nuts and bolts 256

Spontaneously mutating genes 256

Speciating right and left 257

Putting Evolution to the Test 258

Against All Odds: The Fossilization of Lifeforms 259

Bones, teeth, and shell: Body fossils 259

Just passing through: Trace fossils 260

Correcting for Bias in the Fossil Record 261

Hypothesizing Relationships: Cladistics 262

Chapter 18: Time before Time Began: The Precambrian 265

In the Beginning Earth’s Creation from a Nebulous Cloud 266

Addressing Archean Rocks 267

Creating continents 267

Revving up the rock cycle 267

Feeling hot, hot, hot: Evidence for extreme temperatures 269

Originating with Orogens: Supercontinents of the

Proterozoic Eon 270

Single Cells, Algal Mats, and the Early Atmosphere 271

Hunting early prokaryotes and eukaryotes 271

You know it as pond scum: Cyanobacteria 272

Waiting to inhale: The formation of Earth’s atmosphere 275

Questioning the Earliest Complex Life: The Ediacaran Fauna 278

Chapter 19: Teeming with Life: The Paleozoic Era 281

Exploding with Life: The Cambrian Period 282

Toughen up! Developing shells 282

Ruling arthropods of the seafloor: Trilobites 283

Building Reefs All Over the Place 284

Swimming freely: Ammonoids and nautiloids 285

Exploring freshwater: Eurypterids 287

Spinal Tapping: Animals with Backbones 287

Fish evolve body armor, teeth, and legs? 287

Venturing onto land: Early amphibians 290

Adapting to life on land: The reptiles 290

Planting Roots: Early Plant Evolution 291

Tracking the Geologic Events of the Paleozoic 293

Constructing continents 293

Reading the rocks: Transgressions and regressions 294

Fossilizing carbon fuels 297

Pangaea, the most super of supercontinents 297

Chapter 20: Mesozoic World: When Dinosaurs Dominated 299

Driving Pangaea Apart at the Seams 300

One continent becomes many 300

Influencing global climate 301

Creating the mountains of North America 302

Repopulating the Seas after Extinction 303

The Symbiosis of Flowers 304

Recognizing All the Mesozoic Reptiles 306

Flocking together 308

Climbing the Dinosaur Family Tree 308

Branching out: Ornithischia and Saurischia 308

Horned faces and armor: Ornithischian dinosaurs 309

Long necks and meat eaters: Saurischian dinosaurs 312

Flocking Together: The Evolutionary Road to Birds 313

Laying the Groundwork for Later Dominance: Early

Mammal Evolution 314

Chapter 21: The Cenozoic Era: Mammals Take Over 315

Putting Continents in Their Proper (Okay, Current) Places 316

Creating modern geography 316

Consuming the Farallon Plate 317

Carving the Grand Canyon with uplift 319

Icing over northern continents 320

Entering the Age of Mammals 320

Regulating body temperature 322

Filling every niche 323

Living Large: Massive Mammals Then and Now 323

Nosing around elephant evolution 324

Returning to the sea: Whales 325

Larger than life: Giant mammals of the ice ages 326

Right Here, Right Now: The Reign of Homo Sapiens 327

Arguing for the Anthropocene 329

Altering the climate 329

Shaping the landscape 330

Leaving evidence in the rock record 332

Chapter 22: And Then There Were None: Major Extinction Events in Earth’s History 333

Explaining Extinctions 334

Heads up! Astronomical impacts 334

Lava, lava everywhere: Volcanic eruptions and flood basalts 335

Shifting sea levels 337

Changing climate 337

End Times, at Least Five Times 337

Cooling tropical waters 338

Reducing carbon dioxide levels 338

The Great Dying 339

Paving the way for dinosaurs 340

Demolishing dinosaurs: The K/T boundary 340

Modern Extinctions and Biodiversity 342

Hunting the megafauna 342

Reducing biodiversity 343

Part 6: The Part of Tens 345

Chapter 23: Ten Ways You Use Geologic Resources Every Day 347

Burning Fossil Fuels 347

Playing with Plastics 348

Gathering Gemstones 348

Drinking Water 349

Creating Concrete 349

Paving Roads 350

Accessing Geothermal Heat 350

Fertilizing with Phosphate 350

Constructing Computers 351

Building with Beautiful Stone 351

Chapter 24: Ten Geologic Hazards 353

Changing Course: River Flooding 353

Caving In: Sinkholes 354

Sliding Down: Landslides 354

Shaking Things Up: Earthquakes 355

Washing Away Coastal Towns: Tsunamis 355

Destroying Farmland and Coastal Bluffs: Erosion 356

Fiery Explosions of Molten Rock: Volcanic Eruptions 356

Melting Ice with Fire: Jokulhlaups 357

Flowing Rivers of Mud: Lahars 357

Watching the Poles: Geomagnetism 358

Index 359