Geology For Dummies - Alecia M. Spooner

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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.

      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.

      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!

      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

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