Earth Materials

Components of a Diverse Planet

Dexter Perkins, Kevin Henke, Adam Simon, Lance Yarbrough

• Publisher: CRC Press
• Year: 2019
• ISBN:
  9780429589256
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

There is a large and growing need for a textbook that can form the basis for integrated classes that look at minerals, rocks, and other Earth materials. Despite the need, no high-quality book is available for such a course. Earth Materials is a wide-ranging undergraduate textbook that covers all the most important kinds of (inorganic) Earth materials. Besides traditional chapters on minerals and rocks, this book features chapters on sediments and stratigraphy, weathering and soils, water and the hydrosphere, and mineral and energy deposits. Introductions to soil mechanics and rock mechanics are also included.This book steers away from the model of traditional encyclopedic science textbooks, but rather exposes students to the key and most exciting ideas and information, with an emphasis on thinking about Earth as a system. The book is written in such a manner as to support inquiry, discovery and other forms of active learning. All chapters start with a short topical story or vignette, and the plentiful photographs and other graphics are integrated completely with the text.Earth Materials will be interesting and useful for a wide range of learners, including geoscience students, students taking mineralogy and petrology courses, engineers, and anyone interested in learning more about the Earth as a system.

Part I
Introduction to Earth

1 The Origin of the Elements and Earth

1.1 Orion

Orion is shown in Figure 1.1. It is the brightest and most noticeable winter constellation in the Northern Hemisphere (and summer constellation in the Southern Hemisphere) and is distinctive because of its hourglass figure and the three bright stars that make up Orion’s belt. We easily see it during winter months, but during the summer it does not rise until close to sunrise and so is difficult to discern. The constellation is named after the Greek hunter Orion. In one version of Greek mythology, Orion, a storied huntsman, was placed in the heavens by Zeus after he was killed by an arrow shot by Artemis (twin sister of Apollo and daughter of Zeus and Leto). An alternative legend is that Orion died because of the sting of a giant scorpion (that later became the constellation Scorpius). The myths are inconsistent and perhaps originally did not refer to the same individual.

Figure 1.1Orion in the night sky.

Photo from Akira Fujii/David Malin Images. Inset from Joe Tucciarone.

The Orion constellation contains 8–10 bright stars (Fig. 1.2). Three noticeably aligned stars make up the narrow part of the hourglass, equivalent to Orion’s belt. Two of the brightest stars in the sky, Rigel and Betelgeuse, mark Orion’s left knee and right shoulder. Other bright stars distinguish the sword (or club depending on interpretation) and shield he is carrying and the dagger that is hanging from his belt.

The bright stars in Orion are mostly supergiants, and all of Orion’s visible stars are more massive and brighter than our Sun. They include some of the most distant stars that we can see without the aid of a telescope. Rigel and Betelgeuse are two of the ten brightest stars in the night sky. Rigel is a relatively young blue-white supergiant star, and Betelgeuse is an older red supergiant star. Blue and red refer to the most intense colors of light that the stars emit, but it sometimes takes good eyesight to discern these colors when looking at the stars in the sky. Red supergiants, like Betelgeuse, are the largest stars by volume, but not the most massive, because other stars are much denser.

Figure 1.2The stars of Orion.

However, what sets Orion apart from other constellations is that it includes the Orion Nebula, the brightest nebula in the sky. It is shown in Figure 1.3. We easily see the nebula with the naked eye. It appears as a single star in the dagger hanging from Orion’s belt, but it is not a star. At 1500 light years (10¹⁶ kilometers) away, it is one of the closest nebulas to Earth and is the closest region associated with massive amounts of star formation. A closer look reveals this bright spot to be more diffuse and hazier than most stars and to have a reddish color. Viewing with binoculars or a telescope reveals many more fascinating features.

The Orion Nebula is a nuclear furnace made of a glowing cloud of dust, hydrogen, helium, and super-hot gas called plasma. Red and green hydrogen- and sulfur-rich gases, and some carbon molecules similar to components in car exhaust, surround the white-hot center of the nebula. All these gases are heated to extreme temperatures and blown about by winds generated during star formation. Four to six relatively energetic stars are forming near the center of the nebula, in the nebula’s brightest white-yellow region. The photographs of the Orion Nebula (Fig. 1.4), taken with the Hubble telescope, show four relatively young protoplanetary disks with bright centers. The “hot spots” are the sites of the newly forming stars. At least 700 stars of lesser energy, in various stages of formation, lie within the nebula, and the nebula’s total mass is 2000 times that of our sun. The stars may eventually be at the centers of planetary systems like our solar system.

Nebulas like Orion start as clouds of gaseous hydrogen and helium that collapse toward a focal point due to gravity. Gravitational and kinetic energy cause heating and, when hot enough, nuclear fusion begins. So, hydrogen and helium fuse to create heavier elements, and this process is occurring in many stars within the Orion Nebula. Elements have been created this way since the beginning of the universe, nearly 14 billion years ago, and this is one of only a few processes accounting for all the elements existing today.

Figure 1.3The Orion Nebula.

Photo from NASA.

1.2 The big picture

Figure 1.4Protoplanetary disks in the Orion Nebula.

Photo from NASA.

The universe, also called the cosmos, is everything. It is more than just planets, stars, and galaxies. It includes every known physical object, including our planet Earth, its life forms, and everything else that is on it, including you. The universe, estimated to be more than 93 billion light years (10²⁴ kilometers) in diameter, is all of space and matter together. It has been expanding since it first formed about 13.8 billion years ago.

Gravity causes the matter of the universe to form and collect in large concentrations called galaxies. The word galaxy comes from the Greek galaxias, which means milky, in reference to our galaxy, the Milky Way. The Milky Way Galaxy, the galaxy that contains our solar system, shown in Figure 1.5, appears as a bar with spiral arms composed of giant stars that illuminate interstellar gas and dust. The Sun (labeled in the drawing), and the planets of our solar system, are in part of the galaxy called the Orion Spur; the radial lines and numbers in Figure 1.5 are the galactic longitude in relation to the Sun.

Every galaxy is a collection of gas, dust, stars and star remnants, and dark matter, all orbiting around a center point and held together by gravity. Galaxies range in size from dwarfs to giants. Small ones contain only a few billion stars; large ones may contain as many as 100 trillion stars. Spinning causes galaxies to flatten and become disk shaped, but they have diverse shapes—some are irregular, and others are elliptical, spiral, or spiral with bars extending across them (like our galaxy). Perhaps as many as 200 billion galaxies exist in our visible universe. They are separated by nearly empty space, estimated to contain less than one atom per cubic meter.

The Milky Way is about 100,000 light years (10¹⁸ kilometers) across and contains more than 100 billion stars. In the past, astronomers described the Milky Way as a simple spiral galaxy, like our closest galactic neighbor, the Andromeda galaxy. However, recent research suggests that it is a bar-spiral (Fig. 1.5). The Milky Way is in what astronomers call the Local Group of galaxies, which contains about 40 other galaxies.

In the Northern Hemisphere, on a clear summer night, the Milky Way stretches across the sky, appearing as a diffuse swath of light and stars (Fig. 1.6). When we look up and see the Milky Way, we are seeing an edge view of the entire galaxy. The galaxy’s center is near the “Teapot” in the constellation Sagittarius, which appears on the southern horizon during the Northern Hemisphere summer. So, if you look just right and above Sagittarius, you are looking toward the center of our Milky Way galaxy. Our Sun is one star in the Milky Way’s spiral arms about halfway between the center and outer edge of the galaxy (Fig. 1.5).

The planets, asteroids, and most other bodies of our solar system, shown in Figure 1.7, rotate around Sol (as in the adjective solar), more commonly called the Sun. Earth is the third planet from the sun after Mercury and Venus. It is tempting to think that our planet is special. It might be, but within the past 20 years, astronomers have found evidence of planets orbiting other stars. So, other planets and other solar systems exist where, perhaps, planets could be like ours. Yet, within our solar system, Earth is special because it has liquid water, an atmosphere of nitrogen and oxygen that shields Earth from harmful radiation, a constantly evolving outer crustal layer due to plate tectonics, and life.

A strong solar wind of charged particles, in many ways similar to the gases of the Orion Nebula, blows away from the Sun in all directions (Fig. 1.8). One consequence is that gases are swept away from the inner portions of our solar system. Consequently, the outer planets (Jupiter, Saturn, Uranus, and Neptune) are gaseous, mostly hydrogen and helium, but the inner planets (Mercury, Venus, Earth, and Mars) are mostly composed of solid material. The solid parts of all four inner planets have similar overall compositions. They also have a differentiated structure, meaning they contain layers that have different compositions.

Figure 1.5Conceptual view of our Milky Way galaxy.

Modified from a NASA drawing.

Figure 1.6The Milky Way and two constellations: the Teapot (Sagittarius) and Scorpius.

Photo credit: Stellarium with additions by Bob King.

Figure 1.7The planets and some other bodies of our solar system.

Drawing from NASA.

Figure 1.8The Sun and its solar wind.

Photo from NASA.

The inner planets, unlike the outer planets, also have an evolved atmosphere—significantly different from their original atmospheres—that developed mainly by volcanism delivering gases from planetary interiors to exteriors and by comet impacts that added additional material. Earth’s atmosphere has changed greatly over time and today is 78% nitrogen and 21% oxygen. In contrast, none of the other terrestrial planets contain more than a few percent nitrogen. Additionally, Mars and Venus atmospheres are about nearly all carbon dioxide, and Mercury’s very thin atmosphere is heterogeneous but contains more than 40% oxygen and significant amounts of sodium. Earth also has the perfect temperature range that supports life, and this along with a life-supporting atmosphere separates Earth from the ot...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Contents
• Preface
• About the Authors
• Acknowledgments
• Part I Introduction to Earth
• Part II Fundamental Earth Materials
• Part III Surficial Geology and Resources
• Part IV Engineering Properties
• References
• Index