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...