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- Herausgeber: John Wiley & Sons
- Kategorie: Lebensstil
- Sprache: Englisch
Get a rock-solid grasp on geology Geology For Dummies is ideal reading for anyonewith an interest in the fundamental concepts of geology, whether they're lifelong learners with a fascination for the subject or college students interested in pursuing geology or earth sciences. Presented in a straightforward, trusted format--and tracking to a typical introductory geology course at the college level--this book features a thorough introduction to the study of earth, its materials, and its processes. * Rock records and geologic time * Large-scale motion of tectonic plates * Matter, minerals, and rocks * The geological processes on earth's surface Rock that geology class with Geology For Dummies!
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Veröffentlichungsjahr: 2020
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Geology For Dummies®, 2nd Edition
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Library of Congress Control Number: 2020902701
ISBN 978-1-119-65287-8 (pbk); ISBN 978-1-119-65292-2 (ebk); ISBN 978-1-119-65291-5 (ebk)
Geology For Dummies®
To view this book's Cheat Sheet, simply go to www.dummies.com and search for “Geology For Dummies Cheat Sheet” in the Search box.
Table of Contents
Cover
Introduction
About This Book
Foolish Assumptions
Icons Used in This Book
Beyond the Book
Where to Go from Here
Part 1: Studying the Earth
Chapter 1: Rocks for Jocks (and Everybody Else)
Finding Your Inner Scientist
Focusing on Rock Formation and Transformation
Mapping Continental Movements
Moving Rocks around on Earth’s Surface
Interpreting a Long History of Life on Earth
Chapter 2: Observing Earth through a Scientific Lens
Realizing That Science Is Not Just for Scientists
Using a Methodical Approach: The Scientific Method
Building New Knowledge: A Scientific Theory
Speaking in Tongues: Why Geologists Seem to Speak a Separate Language
Chapter 3: From Here to Eternity: The Past, Present, and Future of Geologic Thought
Catastrophe Strikes Again and Again
Early Thoughts on the Origin of Rocks
Developing Modern Geologic Understanding
Uniformi-what? Understanding the Earth through Uniformitarianism
Pulling It All Together: The Theory of Plate Tectonics
Forging Ahead into New Frontiers
Chapter 4: Home Sweet Home: Planet Earth
Earth’s Spheres
Examining Earth’s Geosphere
Part 2: Elements, Minerals, and Rocks
Chapter 5: It’s Elemental, My Dear: A Very Basic Chemistry of Elements and Compounds
The Smallest Matter: Atoms and Atomic Structure
Chemically Bonding
Formulating Compounds
Chapter 6: Minerals: The Building Blocks of Rocks
Meeting Mineral Requirements
Making Crystals
Identifying Minerals Using Physical Characteristics
Realizing Most Rocks Are Built from Silicate Minerals
Remembering the Nonsilicate Minerals
Gemstones
Chapter 7: Recognizing Rocks: Igneous, Sedimentary, and Metamorphic Types
Mama Magma: Birthing Igneous Rocks
Merging Many Single Grains of Sand: Sedimentary Rocks
Stuck between a Rock and a Hard Place: Metamorphic Rocks
Tumbling through the Rock Cycle: How Rocks Change from One Type to Another
Part 3: One Theory to Explain It All: Plate Tectonics
Chapter 8: Adding Up the Evidence for Plate Tectonics
Drifting Apart: Wegener’s Idea of Continental Drift
Coming Together: How Technology Sheds Light on Plate Tectonics
Chapter 9: When Crustal Plates Meet, It’s All Relative
Density Is Key
Two of a Kind: Continental and Oceanic Crust
Understanding Why Density Matters: Isostasy
Defining Plate Boundaries by Their Relative Motion
Shaping Topography with Plate Movements
Chapter 10: Who’s Driving This Thing? Mantle Convection and Plate Movement
Running in Circles: Models of Mantle Convection
Using Convection to Explain Magma, Volcanoes, and Underwater Mountains
Shake, Rattle, and Roll: How Plate Movements Cause Earthquakes
Part 4: Superficially Speaking: About Surface Processes
Chapter 11: Gravity Takes Its Toll: Mass Wasting
Holding Steady or Falling Down: Friction versus Gravity
Focusing on the Materials Involved
Triggering Mass Movements
Moving Massive Amounts of Earth, Quickly
A More Subtle Approach: Creep and Soil Flow (Solifluction)
Chapter 12: Water: Above and Below Ground
Hydrologic Cycling
Streams: Moving Sediments toward the Ocean
Eroding a Stream Channel to Base Level
Seeking Equilibrium after Changes in Base Level
Leaving Their Mark: How Streams Create Landforms
Flowing beneath Your Feet: Groundwater
Chapter 13: Flowing Slowly toward the Sea: Glaciers
Identifying Three Types of Glaciers
Understanding Ice as a Geologic Force
Eroding at a Snail’s Pace: Landforms Created by Glacial Erosion
Leaving It All Behind: Glacial Deposits
Where Have All the Glaciers Gone?
Chapter 14: Blowing in the Wind: Moving Sediments without Water
Lacking Water: Arid Regions of the Earth
Transporting Particles by Air
Deflating and Abrading: Features of Wind Erosion
Just Add Wind: Dunes and Other Depositional Wind Features
Paving the Desert: Deposition or Erosion?
Chapter 15: Catch a Wave: The Evolution of Shorelines
Breaking Free: Waves and Wave Motion
Shaping Shorelines
Categorizing Coastlines
Part 5: Long, Long Ago in This Galaxy Right Here
Chapter 16: Getting a Grip on Geologic Time
The Layer Cake of Time: Stratigraphy and Relative Dating
Show Me the Numbers: Methods of Absolute Dating
Relatively Absolute: Combining Methods for the Best Results
Eons, Eras, and Epochs (Oh My!): Structuring the Geologic Timescale
Chapter 17: A Record of Life in the Rocks
Explaining Change, Not Origins: The Theory of Evolution
The Evolution of a Theory
Putting Evolution to the Test
Against All Odds: The Fossilization of Lifeforms
Correcting for Bias in the Fossil Record
Hypothesizing Relationships: Cladistics
Chapter 18: Time before Time Began: The Precambrian
In the Beginning … Earth’s Creation from a Nebulous Cloud
Addressing Archean Rocks
Originating with Orogens: Supercontinents of the Proterozoic Eon
Single Cells, Algal Mats, and the Early Atmosphere
Questioning the Earliest Complex Life: The Ediacaran Fauna
Chapter 19: Teeming with Life: The Paleozoic Era
Exploding with Life: The Cambrian Period
Building Reefs All Over the Place
Spinal Tapping: Animals with Backbones
Planting Roots: Early Plant Evolution
Tracking the Geologic Events of the Paleozoic
Chapter 20: Mesozoic World: When Dinosaurs Dominated
Driving Pangaea Apart at the Seams
Repopulating the Seas after Extinction
The Symbiosis of Flowers
Recognizing All the Mesozoic Reptiles
Climbing the Dinosaur Family Tree
Flocking Together: The Evolutionary Road to Birds
Laying the Groundwork for Later Dominance: Early Mammal Evolution
Chapter 21: The Cenozoic Era: Mammals Take Over
Putting Continents in Their Proper (Okay, Current) Places
Entering the Age of Mammals
Living Large: Massive Mammals Then and Now
Right Here, Right Now: The Reign of Homo Sapiens
Arguing for the Anthropocene
Chapter 22: And Then There Were None: Major Extinction Events in Earth’s History
Explaining Extinctions
End Times, at Least Five Times
Modern Extinctions and Biodiversity
Part 6: The Part of Tens
Chapter 23: Ten Ways You Use Geologic Resources Every Day
Burning Fossil Fuels
Playing with Plastics
Gathering Gemstones
Drinking Water
Creating Concrete
Paving Roads
Accessing Geothermal Heat
Fertilizing with Phosphate
Constructing Computers
Building with Beautiful Stone
Chapter 24: Ten Geologic Hazards
Changing Course: River Flooding
Caving In: Sinkholes
Sliding Down: Landslides
Shaking Things Up: Earthquakes
Washing Away Coastal Towns: Tsunamis
Destroying Farmland and Coastal Bluffs: Erosion
Fiery Explosions of Molten Rock: Volcanic Eruptions
Melting Ice with Fire: Jokulhlaups
Flowing Rivers of Mud: Lahars
Watching the Poles: Geomagnetism
Index
About the Author
Supplemental Images
Advertisement Page
Connect with Dummies
End User License Agreement
List of Tables
Chapter 5
TABLE 5-1 Common Elements in Earth’s Crust
Chapter 6
TABLE 6-1 Silicate Mineral Groups
TABLE 6-2 Common Carbonate Minerals
TABLE 6-3 Sulfide and Sulfate Minerals
TABLE 6-4 Common Oxide Minerals
TABLE 6-5 Common Native Element Minerals
Chapter 7
TABLE 7-1 Classification of Igneous Rocks
TABLE 7-2 Detrital Sedimentary Rocks
TABLE 7-3 Chemical Sedimentary Rocks
TABLE 7-4 Metamorphic Rocks
Chapter 9
TABLE 9-1 Characteristics of Oceanic and Continental Crust
Chapter 11
TABLE 11-1 Types of Mass Wasting
Chapter 16
TABLE 16-1 Commonly Used Radioactive Isotopes for Dating
Chapter 18
TABLE 18-1 Comparing Banded Iron Formations (BIFs) and Continental Red Beds (CRB...
Chapter 19
TABLE 19-1 Major Developments in Paleozoic Plant Evolution
List of Illustrations
Chapter 2
FIGURE 2-1: a) Pie graph; b) Bar graph; c) Line graph; d) Scatterplot.
Chapter 3
FIGURE 3-1: In this sketch of rock layers, the oldest is A, and the youngest is...
Chapter 4
FIGURE 4-1: The five major spheres of Earth’s planetary system.
FIGURE 4-2: The path of wave travel if Earth’s interior were a continuous solid...
FIGURE 4-3: The recorded path of P waves and S waves.
FIGURE 4-4: The layers of the earth.
Chapter 5
FIGURE 5-1: The parts of an atom.
FIGURE 5-2: The parts of one square of the periodic table of elements.
FIGURE 5-3: The periodic table of the elements.
FIGURE 5-4: The ionic bond between sodium and chloride to form a molecule of Na...
FIGURE 5-5: Covalent bonding in a water molecule.
FIGURE 5-6: Metallic bonding between atoms in a sea of electrons.
Chapter 6
FIGURE 6-1: Mohs relative mineral hardness scale.
FIGURE 6-2: Cleavage planes of muscovite, feldspar, halite, and flourite.
FIGURE 6-3: The appearance of a conchoidal mineral fracture.
FIGURE 6-4: The silicon-oxygen tetrahedron.
FIGURE 6-5: The single chain silicate structure.
FIGURE 6-6: The double chain silicate structure.
FIGURE 6-7: The sheet silicate structure.
FIGURE 6-8: The framework silicate structure.
FIGURE 6-9: The ring silicate structure.
Chapter 7
FIGURE 7-1: Bowen’s reaction series.
FIGURE 7-2: Features of a volcano.
FIGURE 7-3: Features of a shield volcano.
FIGURE 7-4: Features of a stratovolcano or composite cone.
FIGURE 7-5: Features of a cinder cone volcano.
FIGURE 7-6: Types of intrusive igneous features.
FIGURE 7-7: Mechanical weathering of a rock into sediment.
FIGURE 7-8: Weathering by exfoliation.
FIGURE 7-9: Poorly sorted and well-sorted sediments.
FIGURE 7-10: Cross-bedding.
FIGURE 7-11: Graded bedding.
FIGURE 7-12: Current ripple marks.
FIGURE 7-13: Mud cracks.
FIGURE 7-14: Contact metamorphism.
FIGURE 7-15: Index minerals in shale metamorphism.
FIGURE 7-16: Indirect and direct pressure.
FIGURE 7-17: The foliation of minerals by direct pressure.
FIGURE 7-18: The rock cycle.
Chapter 8
FIGURE 8-1: The continents today.
FIGURE 8-2: South America and Africa connected.
FIGURE 8-3: Distribution of fossil evidence on Gondwana continents.
FIGURE 8-4: Stratigraphic sequences of rock from continents, suggesting they we...
FIGURE 8-5: Reconstruction of the continents together, based on glacial striati...
FIGURE 8-6: The continents forming Laurasia.
FIGURE 8-7: The relative age of oceanic crust along the seafloor of the Atlanti...
Chapter 9
FIGURE 9-1: The equilibrium line for continental and oceanic crust.
FIGURE 9-2: Characteristics of a mid-ocean ridge and rift valley.
FIGURE 9-3: A region of active rifting around the Arabian Peninsula and Africa.
FIGURE 9-4: A continental-oceanic plate convergent boundary subduction zone and...
FIGURE 9-5: An oceanic-oceanic convergent plate boundary and associated geologi...
FIGURE 9-6: A continental-continental plate convergent boundary and associated ...
FIGURE 9-7: Features of a transform boundary.
FIGURE 9-8: Fracture zone transform faulting across a mid-ocean divergent bound...
FIGURE 9-9: Three types of rock stress.
FIGURE 9-10: Anticline and syncline features.
FIGURE 9-11: Dome and basin features.
FIGURE 9-12: Features of a fault.
FIGURE 9-13: Dip-slip faults.
FIGURE 9-14: Accretion of volcanic islands onto continental crust.
Chapter 10
FIGURE 10-1: A cross-section of the earth illustrating the focus of each model ...
FIGURE 10-2: A cross-section view of how a volcanic island arc is created.
FIGURE 10-3: A cross-section view of how a continental margin arc is created.
FIGURE 10-4: The Pacific Plate moving across a volcanic hot spot created (and c...
FIGURE 10-5: A seismometer.
FIGURE 10-6: A seismogram of S and P waves.
Chapter 11
FIGURE 11-1: In (a), the friction overcomes the pull of gravity, so everything ...
FIGURE 11-2: Sediments of different grain size have different angles of repose.
FIGURE 11-3: Stream erosion, undercutting the angle of repose, leads to mass wa...
FIGURE 11-4: Rock falls occur when materials fall through the air from a steep ...
FIGURE 11-5: A slide of intact rock material and a slump leaving a scarp.
FIGURE 11-6: As soil creep occurs, objects in the soil begin to tilt downhill.
Chapter 12
FIGURE 12-1: Earth’s hydrologic cycle.
FIGURE 12-2: A watershed.
FIGURE 12-3: (a) Laminar flow; (b) turbulent flow.
FIGURE 12-4: (a) Dendritic drainage; (b) rectilinear drainage; (c) radial drain...
FIGURE 12-5: A braided stream channel.
FIGURE 12-6: A meandering stream channel that creates an oxbow lake.
FIGURE 12-7: Beneath the surface as water infiltrates sediment and rock layers.
FIGURE 12-8: Springs often occur on hillsides, where groundwater flows out onto...
FIGURE 12-9: Groundwater heated by magma rises to the surface as a geyser.
Chapter 13
FIGURE 13-1: Glacier zones of accumulation and ablation.
FIGURE 13-2: Landscape features of alpine glacial erosion.
FIGURE 13-3: How ice sheet flow creates a roche moutonnée.
FIGURE 13-4: Different types of glacial moraines.
FIGURE 13-5: Features of glacial deposition.
FIGURE 13-6: Milankovitch cycles of (a) eccentricity, (b) obliquity, and (c) pr...
Chapter 14
FIGURE 14-1: Creep, bed load, and suspended load layers in a wind current.
FIGURE 14-2: Creation of a ventifact by abrasion.
FIGURE 14-3: A typical sand dune.
FIGURE 14-4: Creation of bedding on the dune slip face and the appearance of cr...
FIGURE 14-5: Dune types.
FIGURE 14-6: Desert pavement created by wind erosion.
FIGURE 14-7: The formation of desert pavement through deposition.
Chapter 15
FIGURE 15-1: Parts of a wave.
FIGURE 15-2: Oscillatory wave motion.
FIGURE 15-3: Transition of waves from oscillatory to translatory motion in shal...
FIGURE 15-4: The pull of the moon creates a bulge, resulting in tides.
FIGURE 15-5: Generating a longshore current.
FIGURE 15-6: Motion of a rip current.
FIGURE 15-7: Coastal features of erosion.
FIGURE 15-8: Features of coastal deposition.
Chapter 16
FIGURE 16-1: How an angular unconformity is created.
FIGURE 16-2: How a disconformity is created.
FIGURE 16-3: The Grand Canyon exhibits a nonconformity (1), an angular unconfor...
FIGURE 16-4: Alpha decay of a radioactive isotope.
FIGURE 16-5: Beta decay of an isotope.
FIGURE 16-6: Beta capture of an isotope.
FIGURE 16-7: The geologic timescale.
Chapter 17
FIGURE 17-1: Trace fossils include tracks and burrows.
FIGURE 17-2: Two styles of cladograms, or phylogenetic trees.
Chapter 18
FIGURE 18-1: Cratons of the modern continents.
FIGURE 18-2: A prokaryotic cell and a eukaryotic cell.
FIGURE 18-3: The biological process of photosynthesis.
FIGURE 18-4: Formation of a stromatolite as algae strands trap sediments.
Chapter 19
FIGURE 19-1: A trilobite.
FIGURE 19-2: Changes in ammonoid shell sutures through time.
FIGURE 19-3: A straight-shelled nautiloid from the Paleozoic.
FIGURE 19-4: A eurypterid.
FIGURE 19-5: An ostracoderm, the earliest fish.
FIGURE 19-6: Armored head bones of a Dunkleosteus.
FIGURE 19-7: Plants common in the Carboniferous coal swamps of the Paleozoic: L...
FIGURE 19-8: The pattern of sedimentary rock formation in the ocean.
FIGURE 19-9: Rock types indicating a marine transgression.
FIGURE 19-10: Rock types indicating a marine regression.
Chapter 20
FIGURE 20-1: The arrangement of modern continents when they formed Pangaea.
FIGURE 20-2: North America during the Mesozoic era.
FIGURE 20-3: Planktonic foraminifera.
FIGURE 20-4: The reptile family tree.
FIGURE 20-5: A flying reptile of the Mesozoic, the pteranodon.
FIGURE 20-6: Bird- and lizard-like hip structure of dinosaurs.
FIGURE 20-7: Ornithischian dinosaurs.
FIGURE 20-8: Saurischian dinosaurs.
Chapter 21
FIGURE 21-1: The Alpine-Himalayan orogenic belt.
FIGURE 21-2: The Circum-Pacific belt, called the Ring of Fire.
FIGURE 21-3: Geographic features of North America formed during the Cenozoic.
FIGURE 21-4: A
Uintatherium
mammal from the Eocene epoch.
FIGURE 21-6: Mammoth and mastodon teeth.
FIGURE 21-5: A Moeritherium.
FIGURE 21-7: Stages in whale evolution from land-dwelling to fully aquatic mari...
Chapter 22
FIGURE 22-1: Regions of the modern continents covered in flood basalt rock laye...
FIGURE 22-2: Extinction rates for five major extinction events.
FIGURE 22-3: The location of the Chicxulub crater in the Gulf of Mexico.
Guide
Cover
Table of Contents
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Introduction
Geology is the study of the earth. By default this means that geology is a vast, complex, and intricate topic. But “vast, intricate, and complex” does not necessarily mean difficult. Many folks interested in geology just don’t know where to start. Minerals? Rocks? Glaciers? Volcanoes? Fossils? Earthquakes? The sheer number of topics covered under the heading “geology” can be overwhelming.
Enter Geology For Dummies! The goal of this book is to break through the overwhelming array of geology information and provide a quick reference for key concepts in the study of the earth.
My hope is that you find this book both interesting and useful, whether you’ve purchased it to accompany a course you’re taking in school or to help you find answers to questions you have about the planet you live on.
About This Book
In Geology For Dummies, you can start anywhere. This book is written as an introduction to the most common topics in geology. Follow your interest from one topic to the next, or start at the beginning and read the chapters in order. I wrote the book in a style that allows you to open to any page and learn something. But if you want to start at the beginning, you’re introduced to the concepts in a logical and structured order that (I hope!) answers your questions almost as soon as you ask them.
Throughout the book you find cross-references to other chapters. I use them because it’s impossible to explore one topic in geology without touching on many others. The multiple cross-references weave together the different parts of geologic study into a complex whole.
Wherever possible, I include illustrations to accompany my explanations. Geology is all around you, so while you are busy reading this book and examining the illustrations, I encourage you to also look around and find real-world examples of the processes and features I describe. To this end, I have also included a color photo section in the middle of the book featuring vivid images that help bring the subject matter to life.
Foolish Assumptions
As I was writing this book, I had to make a few assumptions about you, the reader. I assume that you live on Earth and are familiar with rocks, streams, and weather (rain, wind, and sun). I also assume that you are familiar with a very basic geography of the earth, including the continents, oceans, and major mountain ranges.
I do not assume that you have any scientific background in chemistry, which you may find useful if you want to dig deeper into the details of rock formation and transformation. Similarly, when I discuss evolution I do not assume that you have any background in biology or anatomy (and none is needed to understand the concepts I present). If the subject of evolution interests you, you may find that your questions lead you to pick up other reference books on that topic.
If you find that your interest in geology is further fueled by this book, I recommend that you purchase an earth science or geology dictionary. Geology is full of terms with precise and informative meanings. With this kind of dictionary on hand, you’ll find you can easily interpret even the most befuddling geological explanations.
Icons Used in This Book
Throughout this book, I use icons to draw your attention to certain information:
The Tip icon indicates information that may be especially useful to you as you prepare for a geology exam or assignment or as you begin studying geology on your own.
This icon, which appears only rarely in this book, points out situations that may be dangerous.
Information highlighted with the Remember icon is foundational to understanding the concept being explained. Sometimes this icon indicates a definition or concise explanation. Other times it indicates information that will help you tie multiple concepts together.
This icon indicates that the information goes a little beyond the surface into some technical details. These details are not necessary for your broad understanding of the topic or concepts, but you may find them interesting and informative.
Beyond the Book
In addition to what you’re reading right now, this product also comes with a free access-anywhere Cheat Sheet that tells you about plate tectonics and the geologic timescale.. To get this Cheat Sheet, simply go to www.dummies.com and type Geology For Dummies Cheat Sheet in the Search box.
Where to Go from Here
You have most likely purchased this book with a question about geology already in mind. In that case, I encourage you to follow your interest. Use the table of contents or index to find where I answer your question, flip to that page, and get started!
If you don’t have a particular question in mind, here are a few of my favorite topics that will get you started on your study of Earth:
Chapter
8
, “Adding Up the Evidence for Plate Tectonics”:
In this chapter, I tell you the story of how an early geologist, Alfred Wegener, began to think about plate movements. He collected evidence to support his ideas, but it took many years before the idea of plate tectonics was accepted by the scientific community. This chapter is a great introduction to how science really happens, as well as an overview of the foundational theory of modern geology.
Chapter
12
, “Water: Above and Below Ground”:
If you want to get started by reading about something you can relate to, start with flowing water. Streams and rivers are the most common geologic processes on Earth. Regardless of where you live, you have probably witnessed the action of flowing water moving sediment or rocks. This chapter provides details from how water picks up and carries particles, to how rivers carve canyons and caves. It also covers the topic of groundwater, which is where most of the water you drink comes from.
Chapter
18
, “Time before Time Began: The Precambrian”:
Long ago in Earth’s deep, dark, murky past lay the beginnings of life. This chapter describes the first few billion years of Earth’s existence, from its formation from a gaseous cloud, up to and including the earliest evidence for life — in the form of trace fossils called
stromatolites.
Part 1
Studying the Earth
IN THIS PART …
Discover you are already a scientist, asking questions and seeking answers every day!
Learn the history and development of geologic study.
Go on a guided tour of Earth’s systems, from the atmosphere to the inner core and everything in between.
Chapter 1
Rocks for Jocks (and Everybody Else)
IN THIS CHAPTER
Discovering the scientific study of Earth
Learning how rocks transform through the rock cycle
Putting together plate tectonics theory
Recognizing surface processes
Exploring Earth’s history
Geology and earth sciences seem to have a reputation for being easy subjects, or at least the least difficult of the science courses offered in high school and college. Perhaps that’s because the items observed and studied in geology —rocks — can be held in your hand and seen without a microscope or telescope, and they can be found all around you, anywhere that you are.
However, exploring geology is not just for folks who want to avoid the heavy calculations of physics or the intense labs of chemistry. Geology is for everyone. Geology is the science of the planet you live on — the world you live in — and that is reason enough to want to know more about it. Geology is the study of the earth, what it’s made of, and how it came to look the way it does. Studying geology means studying all the other sciences, at least a little bit. Aspects of chemistry, physics, and biology (just to name a few) are the foundation for understanding Earth’s geologic system, both the processes and the results.
Finding Your Inner Scientist
You are already a scientist. Maybe you didn’t realize this, but just by looking around and asking questions you behave just like a scientist. Sure, scientists call their approach of asking and answering questions the scientific method, but what you do every day is the very same thing, without the fancy name. In Chapter 2, I present the scientific method in detail. Here, I offer a quick overview of what it entails.
Making observations every day
Observations are simply information collected through your five senses. You could not move through the world without collecting information from your senses and making decisions based on that information.
Consider a simple example: Standing at a crosswalk, you look both ways to determine if a car is coming and if the approaching car is going slow enough for you to safely cross the street before it arrives. You have made an observation, collected information, and based a decision on that information — just like a scientist!
Jumping to conclusions
You constantly use your collected observations to draw conclusions about things. The more information you collect (the more observations you make), the more solid your conclusion will be. The same process occurs in scientific exploration. Scientists gather information through observations, develop an educated guess (called a hypothesis) about how something works, and then seek to test their educated guess through a series of experiments.
No scientist wants to jump to a false conclusion! Good science is based on many observations and is well-tested through repeated experiments. The most important scientific discoveries are usually based on the educated guesses, experiments, and continued questioning of a large number of scientists.
Focusing on Rock Formation and Transformation
As I explore in detail in Part 2 of this book, the foundation of geology is the examination and study of rocks. Rocks are, literally, the building blocks of the earth and its features (such as mountains, valleys, and volcanoes). The materials that make up rocks both inside and on the surface of the earth are constantly shifting from one form to another over long periods of time. This cycle and the processes of rock formation and change can be traced through observable characteristics of rocks found on Earth’s surface today.
Understanding how rocks form
Characteristics of rocks such as shape, color, and location tell a story of how and where the rocks formed. A large part of geologic knowledge is built on understanding the processes and conditions of rock formation. For example, some rocks form under intense heat and pressure, deep within the earth. Other rocks form at the bottom of the ocean after years of compaction and cementation. The three basic rock types, which I discuss in detail in Chapter 7, are:
Igneous:
Igneous rocks form as liquid rock material, called
magma
or
lava,
cools. Igneous rocks are most commonly associated with volcanoes.
Sedimentary:
Most sedimentary rocks form by the cementation of sediment particles that have settled to the bottom of a body of water, such as an ocean or lake. (There are also some sedimentary rocks, which are not formed this way. I describe these in
Chapter 7
as well.)
Metamorphic:
Metamorphic rocks are the result of a sedimentary, igneous, or other metamorphic rock being squeezed under intense amounts of pressure or subjected to high amounts of heat (but not enough to melt it) that change its mineral composition.
Each rock exhibits characteristics that result from the specific process and environmental conditions (such as temperature, or water depth) of its formation. In this way, each rock provides clues to events that happened in Earth’s past. Understanding the past helps us to understand the present and, perhaps, the future.
Tumbling through the rock cycle
The sequence of events that change a rock from one kind into another are organized into the rock cycle. It is a cycle because there is no real beginning or end. All the different types of rocks and the various earth processes that occur are included in the rock cycle. This cycle explains how materials are moved around and recycled into different forms on the earth’s surface (and just below it). When you have a firm grasp on the rock cycle, you understand that every rock on Earth’s surface is just in a different phase of transformation, and the same materials may one day be a very different rock!
Mapping Continental Movements
Most of the rock-forming processes of the rock cycle depend on forces of movement, heat, or burial. For example, building mountains requires force exerted in two directions, pushing rocks upward or folding them together. This type of movement is a result of continental plate movements. The idea that the surface of the earth is separated into different puzzle-like pieces that move around is a relatively new concept in earth sciences, called plate tectonics theory (the subject of Part 3).
Unifying geology with plate tectonics theory
For many decades, earth scientists studied different parts of the earth without knowing how all the features and processes they examined were tied together. The idea of plate movements came up early in the study of geology, but it took a while for all the persuasive evidence to be collected, as I describe in Chapter 8.
By the middle of the twentieth century, scientists had discovered the Mid-Atlantic Ridge and gathered information about the age of sea floor rocks across the ridge. With this evidence they proposed the theory of plate tectonics suggesting the earth’s crust is broken into pieces, or plates. Where two plates touch and interact is called a plate boundary.
Exactly how the earth’s crustal plates interact is determined by the type of motion and type of crustal material. These interactions are described as plate boundary types and include:
Convergent boundaries:
At convergent boundaries, two crustal plates are moving toward one another and come together. Depending on the density of the crustal plates, this collision builds mountains, or causes plate
subduction
(meaning one plate goes beneath another), producing volcanoes.
Divergent boundaries:
At divergent plate boundaries, two crustal plates are separating or moving apart from one another. These boundaries are most commonly observed along the sea floor, where the upwelling of magma along the boundary creates a mid-ocean ridge, but they may also occur on continents, such as in the African rift valley.
Transform boundaries:
At transform boundaries, the two plates are neither colliding nor separating; they are simply sliding alongside one another.
In Chapter 9, I provide the details on the different characteristics of continental plates and how they interact as they move around Earth’s surface, including the particular geologic features associated with each plate boundary type.
Debating a mechanism for plate movements
While the unifying theory of plate tectonics has been well-accepted by the scientific community, geologists have yet to agree on what, exactly, drives the movement of continental plates.
Three dominant forces are thought to work together to drive plate tectonic motion:
Mantle convection:
The
convection
of the mantle — the movement of heated rock materials beneath Earth’s crust is thought to be the dominant driver of plate motion. Mantle rock moves outward towards the crust when it is heated, and then cools and sinks back towards the core (sort of like the wax in a lava lamp). As it moves, the crustal plates resting on the outer mantle are carried along.
Ridge-push:
The ridge-push force is a result of new crustal rock forming at a mid-ocean ridge. The addition of new crust at the plate edge will push the plate away from the ridge and towards the plate boundary along its outer or opposite edge.
Slab-pull:
As the ridge is pushing the plate away, the outer edge of such a plate will be sinking into the mantle, and as this slab sinks, it pulls the plate along behind it — creating the slab-pull force.
Mantle convection, ridge-push, and slab-pull forces work together to drive plate tectonic motion. In Chapter 10, you will find more details on how these three forces are constantly reshaping the surface of the earth.
Moving Rocks around on Earth’s Surface
On a smaller than global scale, rocks are constantly being moved around on Earth’s surface. Surface processes in geology include changes due to gravity, water, ice, wind, and waves. These forces sculpt Earth’s surface, creating landforms and landscapes in ways that are much easier to observe than the more expansive processes of rock formation and tectonic movement. Surface processes are also the geologic processes humans are more likely to encounter in their daily lives.
Gravity:
Living on Earth you may take gravity for granted, but it is a powerful force for moving rocks and sediment. Landslides, for example, result when gravity wins over friction and pulls materials downward. The result of gravity’s pull is
mass wasting,
which I explain in
Chapter 11
.
Water:
The most common surface processes include the movement of rocks and sediment by flowing water in river and stream channels. The water makes its way across Earth’s surface, removing and depositing sediment, reshaping the landscape as it does. The different ways flowing water shapes the land are described in
Chapter 12
.
Ice:
Similar to flowing water but much more powerful, ice moves rocks and can shape the landscape of an entire continent through glacier erosion and deposition. The slow-flowing movement of ice and its effect on the landscape are described in
Chapter 13
.
Wind:
The force of wind is most common in dry regions, and you are probably familiar with the landforms it creates, called
dunes.
You may not realize that the speed and direction of wind create many different types of dunes, which I describe in
Chapter 14
.
Waves:
Along the coast, water in the form of waves is responsible for shaping shorelines and creating (or destroying) beaches. In
Chapter 15
, I describe in detail the various coastal landforms created as waves remove or leave behind sediments.
Interpreting a Long History of Life on Earth
One of the advantages of studying geology is being able to learn what mysteries of the past are hidden in the rocks. Sedimentary rocks, formed layer by layer over long periods of time, tell the story of Earth’s living history: changing climates and environments, as well as the evolution of life from single cells to modern complexity.
Using relative versus absolute dating
Scientists use two approaches to determine the age of rocks and rock layers: relative dating and absolute dating.
Relative dating provides ages of rock layers in relation to one another — for example, stating that one layer is older or younger than another is. The study of rock layers, or strata, is called stratigraphy. In methods of relative dating, geologists apply principles of stratigraphy such as these:
Rock layers below are generally older than rock layers above.
All sedimentary rock layers are originally formed in a horizontal position.
When a different rock is cutting through layers of rock, the cross-cutting rock is younger than the layers it cuts through.
These principles and a few others that I describe in Chapter 16 guide geologists called stratigraphers in interpreting the order of rock layers so that they can form a relative order of events in Earth’s history.
However, sometimes simply knowing that something is older than — or younger than — something else is not enough to answer the question being asked. Absolute dating methods use radioactive atoms called isotopes to determine the age in numerical years of some rocks and rock layers. Absolute dating methods may determine, for example, that certain rocks are 2.6 million years old. These methods are based on the knowledge, learned from laboratory experiments, that some atoms transform into different atoms at a set rate over time. By measuring these rates of change in a lab, scientists can then measure the amount of the different atoms in a rock and provide a fairly accurate age for its formation.
If the process of obtaining absolute dates from isotopes seems very complex, don’t worry: In Chapter 16, I explain in much more detail how absolute dates are calculated and how they are combined with relative dates to construct the geologic timescale: a sequence of Earth’s geological history separated into different spans of time (such as periods, epochs, and eons).
Witnessing evolution in the fossil record
The most fascinating story told in the rock layers is the story of Earth’s evolution. To evolve simply means to change over time. And indeed, the earth has evolved in the 4.5 billion years since it formed.
Both the earth itself and the organisms that live on Earth have changed through time. In Chapter 17, I briefly explain the biological understanding of evolution. Much of modern understanding about how species have changed through time is built on evidence from fossilized or preserved life forms in the rock layers. Fossilization occurs through different geologic and chemical processes, but all fossils can be described as one of two forms:
Body fossils:
Remains of an organism itself, or an imprint, cast, or impression of the organism’s body.
Trace fossils:
Remains of an organism’s activity, such as movement (a footprint) or lifestyle (a burrow) but without any indication of the organism’s actual body.
Earth did not always support life. In Chapter 18, I describe the very early Earth as a lifeless, hot, atmosphere-free planet in the early years of the solar system’s formation. It took billions of years before simple, single-celled organisms appeared, and their origins are still a scientific mystery.
Simple, single-celled life ruled Earth for many millions of years before more complex organisms evolved. Even then, millions of years passed with soft-bodied life forms that are difficult to find in the fossil record. It wasn’t until 520 million years ago that the Cambrian explosion occurred. Chapter 19 describes this sudden appearance of shell-building, complex life as well as the millions of years that followed when life was lived almost entirely in the oceans until amphibians emerged on the land.
Chapter 20 delves into the Age of Reptiles, when dinosaurs ruled the earth and reptiles filled the skies and seas. During this period, all the earth’s continents were connected as Pangaea, Earth’s most recent supercontinent. But before the Age of Reptiles ended, Pangaea broke apart into the separate continents you recognize today. Evidence for Pangaea is still visible in the coastal outlines of South America and Africa — indicating where they used to be attached as part of the supercontinent.
In relatively recent time, geologically speaking, mammals took over from reptiles to rule the earth. The Cenozoic era (beginning 65.5 million years ago), which we are still experiencing, is the most recent and therefore most detailed portion of Earth’s history that can be studied in the geologic record (the rocks). Many of the most dramatic geologic features of the modern Earth, such as the Grand Canyon and the Himalayan Mountains, were formed in this most recent era. In Chapter 21, I describe the evolution of mammal species (including humans) and the geologic changes that occurred to bring us to today.
At various times in the history of Earth, many different species have disappeared in what scientists call mass extinction events. In Chapter 22, I describe the five most dramatic extinction events in Earth’s history. I also explain a few of the common hypotheses for mass extinctions, including climate change and asteroid impacts. Finally, I explain how the earth may be experiencing a modern-day mass extinction due to human activity.
Chapter 2
Observing Earth through a Scientific Lens
IN THIS CHAPTER
Finding your inner scientist
Applying the scientific method
Distinguishing scientific laws from scientific theories
Understanding the language of geology
Geology is one of many sciences that study the natural world. Before moving on to the details of geologic science, I want to spend a little time sorting out what exactly science is and does. In this chapter, I describe the elements of science and the scientific method, and I explain how you do science every day perhaps without even realizing it!
Realizing That Science Is Not Just for Scientists
Science is not a secret society for people who like to wear lab coats and spend hours looking into microscopes. Science is simply the asking and answering of questions. Any time you make a decision by considering what you know, collecting new information, forming an educated guess, and figuring out whether your guess is right, you participate in acts of science.
Take a very simple example: choosing a shampoo. You’ve probably tried different types or brands of shampoo, observed how each one leaves your hair looking and feeling, and then decided which shampoo you wanted to purchase the next time. This process of observation, testing, and decision-making is all part of the scientific approach to problem-solving. You follow this process every day in multiple situations as you make decisions about what to buy, what route to take in your car, what to eat for dinner, and so on.
Don’t underestimate the role of science in your daily life. Every interaction you participate in — with the physical world and with other people — is governed by the natural laws discovered and described by scientists in multiple fields of specialization. New products and technologies are the result of ongoing answer-seeking in the sciences. And explanations of how human beings effect and are effected by the natural world are constantly being updated by new scientific discoveries. Keep reading to find out how science is done using a step-by-step approach called the scientific method.
Using a Methodical Approach: The Scientific Method
Scientists seek to answer questions using a sequence of steps commonly called the scientific method. The scientific method is simply a procedure for organizing observations, making educated guesses, and collecting new information. The scientific method can be summarized as the following steps:
Ask a question.
Scientists begin by asking, “Why does that happen?” or “How does that work?” Any question can be the start of your scientific journey. For example, “Why are my socks, which used to be white, now colored pink?”
Form a hypothesis that answers your question.
A
hypothesis
is a proposed answer to your question: an educated guess based on what you already know. In science, a hypothesis must be testable, meaning that you (or someone else) must be able to determine if the hypothesis is true or false through an experiment. For example, “I think my socks turned pink because I washed them with pink laundry soap.”
State a prediction based on your hypothesis that can be tested.
Using the proposed explanation in your hypothesis, form a prediction that you can test. For example, “I predict that if I wash a white T-shirt with pink laundry soap, it will turn from white to pink.”
Design an experiment to test your prediction.
A good experiment is designed to best answer your question (see the upcoming “
Testing your hypothesis: Experiments
” section) by controlling as many factors as possible. For example, to test the above prediction, I will wash one white T-shirt with white laundry soap and one white T-shirt with pink laundry soap. I will wash them in the same washing machine with the same type of water so that everything (except the soap) is the same.
Perform the experiment.
Time to do the laundry! If my prediction is correct, the shirt washed with pink soap will turn pink.
Observe the outcome.
Both white T-shirts are still white after being washed with the different types of soap.
Interpret and draw conclusions from the outcome of the experiment.
Scientists may run a single experiment multiple times in order to get as much information as possible and make sure that they haven’t made any mistakes that could affect the outcome. After they have all this new information, they draw a conclusion. For example, in my experiment, it appears that the color of the laundry soap is not what turns white T-shirts pink in the washing machine. At this point I can propose a new hypothesis about why my T-shirts have turned pink, and I can conduct a new experiment.
Share the findings with other scientists. This is possibly the most important step in the process of science. Sharing your results with other scientists provides you with new insights to your questions and conclusions. In my example, I did not confirm my hypothesis. Quite the opposite: I confirmed that the color of the laundry soap is not responsible for changing the color of my T-shirts. This is still very important information for the community of scientists trying to determine what, exactly, turns white T-shirts pink in the washing machine. Knowing my results will lead other scientists to develop and test new hypotheses and predictions.
Next, I describe in more detail each step of the scientific method approach to answering questions.
Sensing something new
The first step in the scientific method is simply to use your senses. What do you see, feel, taste, smell, or hear? Each of your senses helps you collect information or observations of the world around you. Scientific observations are information collected about the physical world without manipulating it. (Manipulations come later, with experiments; keep reading for the details!)
After you have collected multiple observations, you may find that there is a pattern — each dog you pet feels soft — or you may find that some observations are different from the others — most of the dogs have brown fur, but some have white fur with black spots. By summarizing your observations in this way, you prepare to take the next step in the scientific method, developing a hypothesis.
I have a hypothesis!
After you have summarized your observations, it’s time to propose an educated guess about the processes behind the patterns you observe. That educated guess is your hypothesis. In everyday speech people often say, “I have a theory” when they really mean “I have a hypothesis.” (I’ll get to theories in a few pages.)
A hypothesis is an inference about the patterns you have observed, based on your observations and any previous knowledge you have about the topic. It’s possible to have many different hypotheses about the observed patterns. How do you know which one is correct? You test it with an experiment, which I describe next.
Testing your hypothesis: Experiments
Now the real fun begins: experimenting to determine if one of your hypotheses is correct. Scientists use their hypotheses to develop predictions that can be tested. Based on the observations about the color of dog fur, a prediction could be this: “I predict that all dogs have either brown fur or white fur with black spots.” The prediction is a restatement of my hypothesis, based on my observations.
To determine if my prediction is correct I need to collect more information. I will make new observations, but this time I will manipulate the situation and observe the outcome. In other words, this time my observations will be the result of an experiment.
In science, the experimental design, or the way you go about collecting the new information, is very important. An experimental design describes the parameters of your experiment: how many samples you will take (how many observations you will make) and how you will choose those samples. These decisions are partly determined by the question you are asking and partly determined by the nature of the observations you are collecting.
In most cases it’s impossible to observe every single instance of the physical world that you are exploring. Therefore, you must take a sample that can represent the rest. For example, I can’t look at every dog in the world to see what color their fur is, so I may decide that looking at 100 dogs will provide me with enough observations to determine if my prediction is correct. Those 100 are a sample of the worldwide population of dogs. If I choose those 100 dogs wisely, they may be a very accurate representation of the worldwide dog population. The best sample size is different for each experiment; it all depends on the question being asked.
In earth science, experiments are often natural or observational. This means that scientists go out into the field and observe events that have already happened, such as the formation of rocks, rock layers, or features of the landscape. Scientists make these observations without changing any aspect of the event or its result.
Geologists also use another kind of experiment called a manipulative experiment. A manipulative experiment is done in a laboratory, where the scientist can manipulate or change certain factors in order to test which factors are most important in creating the observed outcome. In this case, multiple experiments can be done, each one testing the importance of a different factor (or variable), with the goal of zeroing in on the one (or ones) that explain the observed outcome.
Most importantly, a scientific experiment, whether it is a natural or manipulated experiment, must be repeatable. This means that the scientists must clearly describe the steps they have taken so that another scientist can repeat the same experiment and see if she too, gets the same result.
Crunching the numbers
After running experiments and making observations, a scientist is left with a large collection of information, or data, to use to draw a conclusion. Trying to find patterns in page after page of descriptive observations or lists of numbers is almost impossible. To find patterns in the data, a scientist uses statistics.
Statistics are a mathematical tool for describing and comparing information (observations) quantitatively, which simply means using numbers. By using numbers to describe the data, such as the number of times a certain characteristic is observed in different rock samples, scientists can organize and compare the patterns in the data using simple arithmetic.
Some people find statistics intimidating because they seem like complicated mathematical formulas. But really, statistical methods are simple mathematics combined in a step-by-step sequence to uncover patterns in the data. Some statistics determine if two sets of data have overall similarities or differences. Others determine which variables are most important in creating the observed outcomes.
Another reason scientists organize and describe their data quantitatively is so that they can display it using graphs. Many different types of graphs are used, and a scientist must determine which type of graph best displays the data in an understandable way. The most suitable graph depends on what type of data is being displayed. Figure 2-1 illustrates a few common graph types used in earth science:
Pie graph:
This type of graph is best used for illustrating different pieces of a whole. The total of a pie chart must always add up to 100 percent.
Bar graph:
Also called
histograms,
bar charts are used to display information that can be sorted into different categories.
Scatterplot:
Scatterplot graphs illustrate how two types of data are related. Sometimes a scientist will use a scatterplot to look for patterns of relationship between the data types — by finding clusters of data points.
Line graph:
This type of graph is most commonly used to plot changes in a type of data over time, distance, or other variable.
FIGURE 2-1: a) Pie graph; b) Bar graph; c) Line graph; d) Scatterplot.
Interpreting results
After data has been described, compared, and graphed, the next step is interpreting the data to draw new conclusions and perhaps propose a new hypothesis for further testing. Often scientists will find that the patterns in their data bring up new questions for exploration.
If an experiment is designed well, the outcome (and collected data) should clearly prove or disprove the initial hypothesis. It is much easier and more common for a scientist to prove a hypothesis wrong than to prove it right. Finding that the hypothesis is incorrect helps rule out wrong ideas and is a very important step toward eventually finding an answer to larger questions that are being asked — and toward determining which hypothesis to test next.
The challenge at this stage is applying previous knowledge (perhaps from previous experiments) to understand what the patterns in the data — or the relationships between variables — mean. Rather than finding answers to all the questions, scientists often find themselves asking new questions and circling back to the hypothesis stage, preparing to test another hypothesis.
