Chapter 1 - Introduction to Earth Science

This Earth Science course is an introduction to basic knowledge about the physical processes and materials of planet Earth. This website is a reference source for students, and serves as a companion to on-line courses, and class lectures and presentations. Many links to other web-based resources are provided—most links are to (hopefully) stable government websites intended for general science education.

This introductory chapter begins with a basic introduction to science, and then focuses on astronomy with an examination of Earth's place in space and time within the Observable Universe. Following chapters focus on the nature and origin of earth materials (land, sea, and air) and processes shaping and changing the surface of the Earth's physical environment.

Students are encouraged to explore beyond the materials presented herein by searching topics of interest on the Internet or searching through books and other materials found in local library collections. Be sure to click on images for a larger view.

What is Earth Science?

Earth science it the branch of science that deals with the physical nature of the Earth's materials, including rock and landscapes, oceans and water resources, and the atmosphere. Earth Science encompasses the study of all facets of the Earth's physical environment, but can apply to other planets and stellar objects as well. Earth science encompasses the branches of science including:

What do earth scientists do?

The Scientific Method

Making assumptions can be a dangerous thing!

Try the Scientific Method! Two Simple Exercises To Illustrate

Important Concepts In Chemistry and Physics

The following sections provide basic background information that are essential to understanding the physical and chemical properties of matter, particularly related to natural earth materials (rocks, seawater, air, organic matter, etc.).

The chemical characteristics of earth materials reveal information about the environments how and where they are formed, Their characteristics also determine their potential fate when exposed to chemical changes over time. For instance, rocks formed deep underground may not be stable in the surface environment where they are exposed to water, air, temperature changes, or other changing physical and chemical conditions. Much of what is presented throughout this on-line textbook is relevant to discussions on Climate Change - the growing body of evidence that shows how the consumption of fossil fuels (coal, oil, and natural gas), some agricultural practices, and other human interactions with the physical environment are slowly causing changes in the composition and energy interactions in the atmosphere and oceans.

Chemical Bonds

Ionic Bonds

Metallic Bonds

Covalent Bonds

Van der Waals Force (and Friction)

Isotopes (and Radioactivity)

Mass and Density

Electricity and Magnetism

Electricity and magnetism are separate phenomena related to a singular underlying force called electromagnetism. Electricity is related to atomic charges carried by electrons (negative) and protons (positive). The charges are equal but opposite, but protons have mass nearly 1,830 greater than electrons. (Neutrons have the same mass as protons, but have no electrical charge). As a result, electrons are freer to move than protons (hindered by their greater mass).

Electromagnetism is a force generated between electrically charged particles on a subatomic level. Within atoms, positively charged protons are trapped in the nucleus, whereas negatively charged electrons are in motion outside a nucleus. Electrons move in static shell-like orbits around the positively charged nucleus. Electrons are attracted to the positive forces of atomic nuclei (protons) but are repelled by other electrons (basically, opposites attract, similarly charged particles repel each other). Electrons are capable of being pulled away or expelled from atoms by attraction by other atoms or external energy forces.

Under the right conditions, with certain types of matter (such as iron in magnets, copper wires, and all substances that are metallic in nature) allow electrons to flow between atoms—this flow creates an electrical current (electricity). This flow of electrons generates a magnetic field, with the intensity of the magnetism generated is proportional to the volume or intensity of electrical flow. A magnetic field extends onto space beyond the matter generating the electrical current (Figure 1-16). As a result, magnets have positively and negatively ends—oppositely charged ends attract each other, where as similarly charged ends repel each other.

The Earth and other planets have special characteristics that allow them to generate great magnetic fields that extend into outer space (Figure 1-17). A compass is an instrument containing a pointer composed of a magnet that aligns itself with Earth’s magnetic field, pointing in the direction toward Earth’s magnetic north pole. Earth's magnetic field is preserved in iron-bearing rocks when they form. Earth's magnetic field is also responsible for the aurora borealis (Northern Lights) and aurora australis (Southern Lights) (discussed below).

The Electromagnetic Spectrum

● Photons are quantum features that have no mass but behave both like a vibrational wave and a particle, simultaneously. Photons transmit both energy and momentum.

● Photons travel at the speed of light, which in the vacuum of space is about 2.998 x 10⁸ meters per second, or about 186,000 miles per second.

● A discrete amount of energy is associated with a photon and is proportional to the vibrational frequency and wavelength of the electromagnetic wave—the faster the vibrational frequency, the shorter wavelength and the higher the energy transmitted.

● Photons can be destroyed or created when they are absorbed or emitted from atoms or atomic particles with mass. On a subatomic level, electromagnetic energy is either released or absorbed as electron orbits shift closer or further from the atomic nucleus.

● Photons move in a linear motion, such as illustrated by a ray of light radiating away from a light source.

Energy

Energy is the capacity for doing work. Energy may exist in various forms: chemical, electrical, nuclear, potential, kinetic, and other forms. Energy is integral to all processes taking place in our physical environment ranging from incoming sunlight to the movement of wind and water, weather, earthquakes, volcanic eruptions.

Most Abundant Elements In Earth's Physical Environment

What Is the Chemical Composition of the Earth's Crust?

Rock samples collected from around the world show that the chemical composition of the Earth's crust is not uniform, but certain elements are much more abundant than others (Figure 1-21).

Note that oxygen and silicon are the two most abundant elements in the Earth's crust. Therefore, compounds that contain some silicon and oxygen are most abundant in rocks in the Earth's crust. These compounds occur as common silicate minerals that occur in abundance wherever rocks of certain origins occur on the surface.

Early Contributions to Earth Science and Astronomy

Aristotle

Discoveries Leading To Modern Astronomy

Early Astronomers: Copernicus, Galileo, Kepler, and Newton

Gravity

Understanding Geologic Time

At the time of Galileo in the 16th Century, the general knowledge of the age of the Earth was interpreted by the biblical Genesis story and associated discussions by Greek and Roman philosophers. Early investigations in geology focused on describing landscape features, classifying rocks, minerals, geologic features, and mapping. As explorers returned with discoveries and maps from missions around the world, libraries and museums began to fill with enough materials for people to begin to recognize patterns in geologic data. Most of the early works in modern geology came out of Europe's scientific community. Although many thousands of individuals have contributed important ideas, several people stand out for making important early contributions, often at the risk of their own lives and well-being. The notion that the Earth was old (measured in billions of years) has not been all that popular with some religious organizations throughout the ages.

Although fossils have been marveled at throughout history, it was heresy to describe them as ancient life forms (for instance, Leonardo Da Vinci believed fossils were ancient life forms, older than the stories in the biblical book of Genesis, but he only wrote about it in secrecy). It was was a Danish Catholic bishop, Nicolas Steno (1638-1686), who first promoted science of the origin of fossils and the basic geologic principles associated with the science of stratigraphy.

A fossil is a remnant or trace of an organism of a past geologic age, such as a shell, skeleton or leaf imprint, embedded and preserved in the Earth's crust. The fossils found in ancient layers of strata appear unique to rocks of similar age, wherever they occur. The collective knowledge of fossil evidence from around the world is referred to as the fossil record, and follows a time line through Earth's history.

The Science of Stratigraphy

• earthquakes only happen occasionally, but many earthquakes in an area taking place over millions of years can result in the formation of a mountain range.
• the deposition of silt from annual floods over millions of years can built a great river delta complex.
• the slow growth and accumulation of coral and algal material over time can build a great barrier reef.
  

James Hutton also contributed to a theory of rock formations. A rock formation is the primary unit of stratigraphy, consisting of a succession of strata useful for mapping or description. A rock formation typically consists of a unique lithology (rock type) that has a relatively defined geologic age and is considered mappable (occurs throughout area or region, both on the surface and in the subsurface). The correlation of rock formations (and the fossils they contain) from one region to another lead to the development of the geologic time scale (Figure 1-27 and 1-28).

William Smith (1769–1839) used Hutton's theories to create the first geologic map of strata exposed throughout the British Isles. William Smith's map named Delineation of the Strata of England and Wales with part of Scotland published in 1815 was the first geologic map of an entire country (Figure 1-29). As nations began to understand the importance of geologic mapping for evaluating their natural resources, the science of geology began to grow. Once researchers had access to the distribution of materials and landscape features, they began to try to understand how and why landscape features like mountain ranges formed. What could explain the distribution of continents and oceans around the world? Why were some regions rich in certain kinds of mineral resources and others were not?

During the same period, there was an explosion of knowledge was happening in the world of biology. Swedish biologist, Carl Linnaeus (1707-1788) began the biological naming scheme of binomial nomenclature, establishing a logical way to chart and classify life forms. Taxonomy gave later scientist a means to classify both modern and ancient life forms. This helped Charles Darwin (1809-1882) to first propose a theory of evolution, an essential component to explaining the distribution of fossils through the geologic ages.

The Geologic Time Scale

The Geologic Age of the Earth

Demand For Energy and Mineral Resources Supported Geologic Research in the 20th Century

Fig. 1-26. Layers of strata (beds of sedimentary rocks) exposed in the Grand Canyon.

Fig. 1-27. The geologic time scale provides names to a chronology of established periods of time in the history of Earth and the Universe —time periods range from thousands, millions, and billions of years.

Fig. 1-28. If a second were 100,000 years - this classic diagram show the distribution of a different ages of time as if it were all squeezed into a 24 hour day. All of human history would fit in the last fraction of a second!

Fig. 1-29. William Smith's geologic map of 1815 was the first attempt to map an entire country.
^{(British Museum of Natural History)}

Fig. 1-30. The "Lucas Gusher" in 1901 started the rush to the Spindletop Oil Field in Beaumont, Texas.
^{(Beaumont Historical Society)}

Structure of the Earth (an introduction)

Discussion of the major components of Earth's physical environment involves discussion about the solid materials (rocks and landscapes), water resources, and its atmosphere. Each of these are discussed in more detail in following chapters.

In cross-section, the Earth has a central core, a mantle, and the crust (Figure 1-31).

A core is the innermost part of a rocky planet or moon. Earth's core, based on geophysical studies, is believed to consist of a 758 mile (1220 km) thick magnetic metallic inner core that is overlain by a 1400 mile (2250 km) thick zone of dense molten material in the outer core. This is overlain by the Earth's mantle.

A mantle is an inner layer of a terrestrial planet or other rocky body large enough to have differentiated in composition by density. On Earth, the mantle is a highly viscous layer between the outer core and the crust at the surface.

A crust is the outermost solid shell of a rocky planet or moon, which is chemically distinct from the underlying mantle.
Earth's crust ranges from about 6 to 40 miles thick (10 to 64 km).

The scientific evidence that reveals the structure of the Earth is discussed in detail in Chapter 7.

Earth's Atmosphere (An Introduction)

Earth's Water: The Hydrosphere and Cryosphere (an introduction)

Water moves through the atmosphere (involving evaporation, transport, and precipitation), and flows both on the surface and underground on its journey back to the oceans. The collective actions of water migration is called the hydrologic cycle (Figure 1-33).

The term hydrosphere is used to describe all the waters on the Earth's surface, such as oceans, lakes, rivers, and streams (discussed in Chapter 12).

The cryosphere is the frozen water part of Earth's systems, including all ice trapped in continental glaciers and sea ice (discussed in Chapter 13).

All life on Earth is associated with water. The term biosphere is used to describe all the regions of the surface, subsurface, and atmosphere of the Earth (and possibly other planets) occupied by living organisms.

Fig. 1-33. The hydrologic cycle is illustrated in this concept diagram.

Astronomy

Determining the Expanse of Space

It was in 1923 that Edwin Hubble found dozens of uniquely identifiable variable stars in the Andromeda nebula and then determined that Andromeda was at least 10 time more distant than the most distant stars in the Milky Way. He was first to determine that Andromeda was a separate system which he named a galaxy. The Milky Way is an obvious band of densely distributed stars and clouds of dust visible as a band in the clear night sky (Figure 1-34). Before Hubble's discovery, it was thought to be the Milky Way represented the entire Universe, and that unusual shaped spiral nebulae (galaxies) were part of the Milky Way. With Hubble's discovery, it became evident that Earth and the Sun's Solar System was within the greater Milky Way Galaxy, and that the abundance of other galaxies showed that the Observable Universe was drastically much, much larger that was previously known.

The Andromeda Galaxy is a spiral galaxy (Figure 1-35). It is the closest large galaxy to our Milky Way Galaxy and is one of the few visible to the naked eye. It is the most distant object in space that can be seen without magnification.

The Andromeda Galaxy can be seen in the northern hemisphere on clear autumn nights. It is located about 2.25 million light-years away from Earth. (A light year is the astronomical distance that light can travel in a year; approximately about 9.4607 x 10¹² kilometers or about 6 trillion miles.) Andromeda is estimated to contain about 1 trillion stars. Astronomers estimate that the Milky Way and Andromeda galaxies will eventually collide (merge) in about 4.5 billion years in the future.

Galaxies

A galaxy is a system of millions to trillions of stars, together with gas and dust, held together by gravitational attraction. Deep-space observing telescopes show distant field of galaxies—galaxies and clusters of galaxies can be seen in all directions in distant space. The distance to these objects are in the range of thousands to billions of light years away from Earth.

Figure 1-30 shows a field of galaxies observed in on small region in deep space. Using images like this, astronomers estimate there may be 100 billion galaxies within the Observable Universe.

Galaxies appear as many shapes and sizes, but there are three general classes: spiral, elliptical, and irregular galaxies, but each of these groups are subdivided into classes (Figures 1-36 to 1-39). Small elliptical galaxies are the most common, and unlike spiral galaxies their stars do not seem to revolve around their galactic centers in an organized way. The galactic center is where the greatest mass and concentration of stars exist in a galaxy. Irregular galaxies take on many shapes, and many are interpreted as galaxies that have collided or merged under gravitational attraction.

The Milky Way Galaxy is probably a spiral galaxy.

Fig. 1-36. A field of galaxies.

Fig. 1-37. A spiral galaxy.

Fig. 1-38. An elliptical galaxy

Fig. 1-39. An irregular galaxy

Earth's Place In the Observable Universe

The Big Bang Theory

The Big Bang Theory is a cosmological theory holding that the Observable Universe originated approximately 13.8 billion years ago from the violent explosion of a very small agglomeration of material of extremely high density and temperature (Figure 1-41). Current scientific though is that originally the material ejected from the Big Bang was too hot for subatomic particles with measurable mass to exist. It was probably many thousands of years after the Big Bang that it got cool enough for sub atomic particles and then atoms to form, and that gravitational attraction could influence the newly forming matter. Early in the history of the Universe matter began to condense and with time gravitation attraction pulled materials together to form galaxies.

In 2016, the Hubble Space Telescope was able to capture an image of the furthest distant galaxy known, estimated at about 13.4 billion light years away from Earth.

What is beyond the Observable Universe is unknown. See a NASA website about the Big Bang Theory.

Stars

A star is a self-luminous celestial body consisting of a mass of gas held together by its own gravity. Stars exist in a balance—their internal energy generated by nuclear fusion reactions results in an outflow of energy to the star's surface. This outward flow of directed gas and radiation pressures is balanced by the inward-directed gravitational forces.

Since ancient times, astronomers have been charting stars into constellations—recognizable grouping of starts that appear in the night sky and move with the seasons as the Earth orbits the Sun (Figure 1-42). Although stars in constellation often appear in association by appearance, they may be large distances apart and very greatly in brightness (intensity). In addition, stars exist in a wide range of colors, most obvious when observed through telescopes or from space (Figure 1-43). Many stars are clustered together, often sharing a common stellar history (Figure 1-44). Some stars orbit each other relatively close to one another as binary systems (Figure 1-45). Some star systems have multiples stars in orbit around each other.

Among the millions of stars observable in our galaxy, astronomers have been classifying them by size, color, and brightness (intensity) . Most stars in our galaxy fall into a class called the main sequence of which our Sun belongs (Figure 1-46). Astronomers have developed theories about star formation and the life cycle of stars in their different classes. With years of observation, abundance of knowledge has been gained about the life cycle of stars (Figure 1-47).

Nebulae and the Formation and Life Cycle of Stars and Solar Systems

Stars and solar systems form in giant interstellar clouds called nebulae. A nebula is an interstellar cloud within a galaxy consisting of gas and dust, typically glowing from radiant energy from stars nearby within them (Figures 1-48 to 1-53). Nebulae are the birth place of both stars and other objects within solar systems. Nebulae can form from the explosion of stars at the end of their life cycle, expelling gas and matter into interstellar space. Large nebula eventually begin to contract under the influence of gravity, resulting in the creation of new generations of stars and solar systems.

As stars form, gravity draws material in (mostly gas) and it mass increases until the internal heat and pressure is enough to start nuclear fusion reactions (converting hydrogen into helium), igniting a new star. As stars age, they consume their fuel and eventually run out of nuclear fuel. Stars like the Sun may take billions of years to consume their nuclear fuel. When the fuel runs out, stars collapse under the weight of their own gravity. However, the fate of a star depends upon its mass.

Stars up to about seven times the mass of the Sun fall within the main sequence grouping of stars. These go through stages as they consume their fuel. Young stars fuse hydrogen into helium. When stars run out of their hydrogen, the force of gravity causes them to collapse, which increases the heat and pressure within its core. During this phase of a star's life it will expand and become a red giant. Once the helium in the core of a star is consumed, stars in the main sequence will shed much of their mass into space (creating nebula), and the remaining core will shrink and cool and shrink to become a hot remnant called a white dwarf.

Fate of Supergiant Stars

Stars with masses greater than about seven times the mass of the Sun experience a more spectacular fate. More massive stars will burn through their fuel much faster than stars of the main sequence because their cores are hotter and under greater pressure. One these massive stars burn through their hydrogen and helium, this increase in heat and pressure allows fusion to convert helium into carbon, then carbon into neon, and then into iron. As the star continues to burn through it's fuel it eventually shuts down because it the fusion process of creating iron actually consumes more energy than it produces and the star looses it balance and collapses under it own gravity. The collapsing core reaches temperatures in the range of 100 billion degree and the core recoils as a massive explosion called a nova. Great star collapses produce supernova where a star may shed the majority of it mass into space, creating a new nebulae. What happens to the core depends on the mass of the star. Stars about 7 to 20 times the mass of the Sun produce massively dense objects called neutron stars (their density is so great that electrons and protons collapse to form a great mass of neutrons). Stars with masses greater than about 20 times the mass of the Sun may collapse to form black holes. Black holes of so dense that their gravity prevents light from escaping from within their event horizons where matter is pulled into an inner space where nothing escapes.

Fig. 1-42. A constellation chart of stars visible in the fall night sky.

Fig. 1-43. A view of stars of many different colors in the Alpha Centari region. Color is a reflection of how hot stars are: blue are hottest, red are cooler. White and yellow are intermediate.

Fig. 1-44. The Pleiades star cluster, perhaps the most recognizable constellation, contains over 3000 stars and is about 400 light years away and about 13 light years in diameter.

Fig. 1-45. Albireo is the name of a binary star system visible about 380 light years distant.

The Solar System

The Sun

Structure of the Sun

Fig. 1-56. Internal structure of the Sun.

Fig. 1-57. The Sun's corona is visible during a solar eclipse.

Sunspots and Coronal Mass Ejections

Sunspots are relatively dark patches that appear temporarily on the Sun's photosphere (Figures 1-58 and 1-59). Sunspots are cause by a flux in magnetic fields that appear to inhibit convection. Sunspots usually occur in pairs, like the two ends of a U-shaped magnet. Sunspots last a few days to a few months before they dissipate. The concentration of sunspots on the solar surface tend to follow an 11 year cycle that also flows a small variation is the total amount of solar energy output.

Coronal mass ejections are unusually large eruptions of streaming plasma and radiation (composed of charged particles) under the influence of solar magnetism. Eruptions result in the formation of solar flares and prominences (arching flares) that erupt from the Sun's surface (Figures 1-60 and 1-61). Plasma streaming from the Sun's corona results is the source of the solar wind, and coronal mass ejections in form of large solar flares and prominences can result in solar storms that can severely impact radio communications and potentially satellites orbiting Earth.

The Solar Wind

Solar storms associated with coronal mass ejections can interfere with radio communications, cause damage to satellites, and impact electrical transmission lines and facilities (resulting in power outages). During strong solar storms long lines of metal (like electrical power lines, pipelines, and railroad lines in northern regions can overload with electrical charges which and spark to nearby objects and have been reported to have started brush fires. Because massive solar ejections can be observed, the possible impacts of solar storms can be predicted.

Planets and Planetary Systems of the Solar System

A planet is a large spherical celestial body moving in an elliptical orbit around a star.

A planetary system is a set of gravitationally bound celestial objects in orbit around a star or star system. Planets with orbiting moons are planetary systems. The Solar System consists of four inner rocky planets, four outer gas planets, and orbiting belts of asteroids, comets, planetesimals, and other objects under the gravitation influence of the Sun.

The 4 Inner Rocky Planets
Fig. 1-64. Mercury	Fig. 1-65. Venus	Fig. 1-66. Earth	Fig. 1-67. Mars
• a rocky planet • no atmosphere • no moons • planet radius: 1,516 miles (2440 km) • average distance from sun: 36 million miles (58 million km) • orbital period: 88 days • gravity: 3.7 m/sec2	• a rocky planet • hot atmosphere, mostly CO2 (with a sulfur-rich cloud cover) • no moons • planet radius: 3,760 miles (6050 km) • average distance from sun: 67.24 million miles (108 million km) • rotation (day): -243 day (it rotates backwards!) • orbital period: 224.7 days • gravity: 8.87 m/sec2	• a rocky planet with oceans, ice cap, and atmosphere • supports life! • one moon (the Moon!) • planet radius: 3,959 miles (6370 km) • average distance from sun: 92.96 million miles (150 million km) • rotation (day): 24 hours • orbital period: 365.24 days • gravity: 9.8 m/sec2	• a rocky planet • has ice caps at poles • thin atmosphere, mostly CO2 • 2 small moons (Phobos and Deimos) • planet radius: 2,106 miles (3390 km) • average distance from sun: 141.6 million miles (228 million km) • rotation (day) 24.67 hours • orbital period: 687 days • gravity:
The 4 Outer Gas Planets (or Planetary Systems)
Fig. 1-68. Jupiter	Fig. 1-69. Saturn	Fig. 1-70. Uranus	Fig. 1-71. Neptune
• largest of the gas planets • mostly hydrogen and helium • has 67 moons, of which 4 are much larger than other moons. • very active storms are visible in its atmosphere. • planet radius: 43,441 mile 70,000 km) *average distance from sun: 483.8 million miles (779 million km) • orbital period: 12 years • rotation (day): 9 hr, 56 min	• a gas planet famous for its visible rings (mostly dust, ice, and rock fragments). • Currently has 62 moons, including Titan, the largest in the Solar System. • planet radius: 36,184 miles (36,200 km) • average distance from sun: 888.2 million miles (1.42 billion km) • orbital period: 29 years • rotation (day): 10 hr, 42 min	• a gas planet • has 5 medium-sized moons (many smaller ones too) • planet radius:15,759 miles (25,400 km) • average distance from sun: 1.784 billion miles (2.87 billion km) • orbital period: 84 years • rotation (day): 17 hr, 14 min	• the outermost gas planet • has 13 known moons • planet radius: 15,299 miles (24,620 km) • average distance from sun: 2.795 billion miles (4.5 billion km) • orbital period: 165 years • rotation (day): 16 hr, 6 min

Earth's Moon

Earth's Moon is the fifth largest of at least 168 known moons orbiting planets in the Solar System (Figure 1-72).

The Moon rotates ate the same rate that it revolves around the Earth (a synchronous rotation that keeps the same side of the Moon facing Earth).

The Moon lacks an atmosphere, and does not display any active geologic activity (such as earthquakes or volcanic eruptions). Like Earth, the Moon has a core, mantle, and a crust; geophysical data suggest the part of the Moon's core and mantle may be molten. The lack of atmosphere has helped to preserve geologic features that date back to early stages in the formation of the Solar System.

Most of what we have learned about the physical environment, composition, and origin of the Moon comes from the Apollo Missions (between 1961 and 1975) which culminated in a series of manned Moon landings between 1969 and 1972. Rock and lunar soil sample collected during those missions have helped resolving many questions and supporting theories about the origin of the Earth and Moon within the Solar System (discussed below).

Asteroids and Comets

The Outer Solar System

Nebular Hypothesis of the Origin of the Solar System

Proto-Earth Formed

Formation of the Earth-Moon System

Zones of the Earth Climate System and Seasons

Evolution of Earth’s Layered Structure

Origin of Earth's Atmosphere and Oceans

Water and Oceans On Other Planets and Moons