Processes that Shape the Earth, Third Edition

By Sophia Chen and David Thompson

On Earth, nothing is still. Mountains rise and fall. Tides ebb and flow. Even the continents themselves are on the move. Beneath the surface, a restless engine powers earthquakes, volcanic eruptions, and the shifting of continents. Above ground, the sun causes the wind to howl, rain to pour, rivers to churn, and oceans to swell with waves. Processes That Shape the Earth, Third Edition surveys these forces and the ways they sculpt the planet. The modern theory of plate tectonics is introduced, along with other pertinent topics in physical geology. Several chapters add relevant historical context, presenting readers with fascinating discussions of Earth's origin, its history over billions of years, and the recent changes that have resulted from human activity.

• Language: English
• Publisher: Chelsea House
• Release date: Sep 1, 2021
• ISBN: 9781646937370

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Processes that Shape the Earth, Third Edition

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Contents

Chapters

Introduction to Physical Geology

Overview of Planet Earth

Plate Tectonics

Rocks

Freshwater Forces That Shape the Earth

Historical Geology

Glaciers

Wind Processes that Shape the Earth

The Shoreline

Humans Shape the Earth

Support Materials

Glossary

Bibliography

About the Authors

Index

Chapters

Introduction to Physical Geology

The word geology derives from the Greek words geo, meaning Earth, and logia, meaning study. Literally, geology is the study of Earth, and those who study Earth are called geologists. Many people imagine that geologists only study rocks, but this is far from true. Geologists can be found collecting gases from a volcano, using radar to look beneath the desert sands, drilling holes miles deep into ice, and mapping the ocean floor with sound. The quest to understand our planet takes geologists to some of its most remote locations.

The field has a long history, as humans have studied the planet for thousands of years. The ancient Greeks were among the first to ask basic questions such as, What is the shape of Earth? Today, with a globe in almost every classroom, almost everyone knows Earth is shaped like a sphere. But thousands of years ago, the answer to this question was far less obvious.

In the fourth century B.C., the Greek philosopher Aristotle wrote that Earth is spherical.¹ He arrived at this conclusion not by studying the rocks at his feet, but by studying shadows on the moon. During a lunar eclipse, Earth and the moon are aligned so that Earth casts a shadow on the moon. Aristotle noted that this shadow is always circular. Because the only shape that always casts a circular shadow is a sphere, he concluded that must be Earth's shape.

Other early truth-seekers also made important discoveries about Earth. In 250 B.C., the Greek mathematician Eratosthenes carefully measured the angle of sunlight at two different locations and correctly calculated the size of Earth.²

Although these early researchers learned a great deal, society did not always embrace or propagate their knowledge. Before societies fully embraced the principles of the Enlightenment, Christian religious leaders banned scientific results that they believed conflicted with the divine truth found in the Bible. They especially disliked the field of geology because a careful study of Earth could disprove the Bible's story of a six-day creation.

This led men like James Ussher, the archbishop of Armagh in Ireland, to try and reconstruct Earth's history based on the Bible and other esoteric sources. During the 1600s, he searched the Bible and other ancient sources for information on the Earth's creation. After intensive study, Ussher concluded, that Earth was created on Saturday, October 22, 4004 B.C., at around 6 p.m.³ While this result sounds absurd today, Ussher's calculation was just one of many attempts to determine the age of the Earth. When pressed to explain how all the mountains and valleys could have been made in only 6,000 years, religious philosophers invented catastrophism. The incorrect theory of catastrophism claims that major catastrophes, like the flood in the story of Noah and his ark, shaped Earth's features.

In the 1700s, James Hutton overturned the theory of Biblical catastrophism. Now often celebrated as the father of modern geology, Hutton replaced catastrophism with the principle of uniformitarianism. According to the principle of uniformitarianism, the slow processes at work on Earth today are the same processes that have acted on Earth in the past. Places like Mount Everest and the Grand Canyon were made by the same kinds of changes that are happening today. The slow movement of continents unfolds through millions of years. During equally long times, erosion by rivers carves valleys. To understand how these mountains and valleys formed in the past, Hutton deduced that we should study what is happening on Earth right now. This theory of uniformitarianism was later most famously summarized by the nineteenth century geologist Charles Lyell with the maxim that the present is the key to the past in his work Principles of Geology.

Geology now has two main branches: historical geology and physical geology. Historical geology is the study of Earth's history. Physical geology is the study of the physics, or processes, that shape the Earth. The main topic of this ebook is the field of physical geology. However, physical and historical geology are so closely related that it is impossible to study one without learning something about the other, so chapters include some discussion of Earth's history as well. We begin with a general overview of planet Earth. After a brief discussion of Earth's formation, we introduce Earth's sources of energy and the cycles powered by that energy. The two most important sources of energy are Earth's internal heat and the heat from sunlight.

Earth's internal heat causes the continents to move. The theory of plate tectonics, one of the most important ideas in all of modern geology, describes this process. Aside from explaining the formation of mountains and oceans, plate tectonics also plays an important role in the creation and destruction of rocks.

Sunlight, the other main source of Earth's energy, powers the rain and snow that delivers water from the oceans to the land in a cycle. During the Ice Age, when Earth was much colder than it is today, much more of the atmosphere's water fell on the land as snow instead of rain, creating gigantic chunks of ice called glaciers. These glaciers played a large role in shaping the landscape of Canada, northern Europe, and the northern United States.

The Sun also produces wind by heating the air. Wind can create distinctive features on land. The wind also produces waves on the ocean, and those waves shape the shoreline in various processes.

Humans have become the dominant force at work on Earth today. Powered by fossil fuels, humans have reshaped the land and altered the composition of the atmosphere. These activities have led to shifts in global-scale weather patterns known as climate change, a pressing concern of our time.

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1. Hogenboom, Megan. We Have Known That the Earth is Round for Over 2,000 Years, BBC, January 26, 2016. Available online. URL: http://www.bbc.com/earth/story/20160126-how-we-know-earth-is-round. Accessed July 19, 2021.

2. Ibid.

3. Bressan, David. October 23, 4004 B.C.: Happy Birthday Earth! Scientific American, October 22, 2013. Available online. URL: https://blogs.scientificamerican.com/history-of-geology/october-23-4004-bc-happy-birthday-earth/. Accessed July 20, 2021.

Overview of Planet Earth

The universe began with a big explosion about 14 billion years ago. For lack of a better name, scientists call this the Big Bang. Before the Big Bang, there was no light, no atoms, nor was there even any space or time. The Big Bang created only the three lightest elements: hydrogen, helium, and lithium. In the beginning, the universe was filled with clouds of these three elements and nothing else. How, then, did carbon, oxygen, and all of the other elements get created? Before answering that question, we will first review some facts about atoms.

Elements and Isotopes

Each atom can be described using two pieces of information: its atomic number and its isotope. The atomic number is the number of protons contained in an atom's nucleus. An element—such as hydrogen, carbon, or oxygen—is a group of atoms that all have the same atomic number. For example, every hydrogen atom has atomic number one, every helium atom has atomic number two, and so on.

Thus, all atoms of the same element have the same number of protons. But they do not necessarily have the same number of neutrons. An isotope is a subgroup