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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 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 Universe. Following chapter 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.

Click on images throughout this website for a larger view.
Earthrise as photographed by the Lunar Reconnaissace Orbiter in 2013
Fig. 1-1. Earth rise over the Moon as seen from the Lunar Reconnaissance Orbiter in December, 2013.


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:

    Geology—the study of the Earth. The scientific study of the origin, history, and structure of the earth. The structure of a specific region of the earth's crust. And, the scientific study of the origin, history, and structure of the solid matter of a celestial body. Geology is also subdivided into:

* Physical geology—that branch of geology concerned with understanding the composition of the earth and the physical changes occurring in it, based on the study of rocks, minerals, and sediments, their structures and formations, and their processes of origin and alteration.

* Historical geology
—the study of the composition, relative positions, etc., of rock strata in order to determine their geological history. Historical geology is dependent on concepts and order of events related to deep time, as defined by a geologic time scale.

Hydrology—the branch of science of the earth's water resources, especial it movement in relation to land.

Oceanography—the branch of science concerned with the physical and biological properties of the world's oceans, seas, and coastal marine environments.

Meteorology—the branch of science concerned with atmospheric processes and phenomena, including weather.

Astronomy—the branch of science that concerns celestial objects in space, and physical Universe as a whole. The physical environments of other planets and objects in the Solar System provide insights into what is happening here on Earth (utilizing space-based observation of the Earth's systems (earth, water, and air).

What do earth scientists do?
* Earth scientist study earth processes: floods, storms and atmospheric phenomena, earthquakes, landslides, volcanic eruptions.
* Earth scientists explore and manage resources: marine resources, oil & gas, water, metals, rock byproducts.
* Earth scientists work in environmental fields: climate change, water and waste management, and resource protection.
* Earth scientists work in construction and engineering: archeology, urban planning, coastal and marine port management.
* Earth scientists serve in national security and are involved in public health and safety.
* Earth scientists study ocean basins, glaciers, predict weather patterns, and are involved in space exploration programs.
* Earth scientists work in education: schools, parks, and museums.

Federal organizations conduct research and employ many earth scientists. Note that the abbreviations for these agencies are used throughout this website.
Name and Abbreviation website
National Oceanic and Atmospheric Administration (NOAA)
Many states and cities also have agencies that employ marine scientists.

Scientists are involved in all aspects of management of water resources, coastal and marine wildlife resources and fisheries. They conduct natural hazard investigations. They work for organizations involved with with offshore energy extraction and with shipping and port management.

Many teachers in public schools and colleges have degrees in marine sciences!

For instance, in California, many marine scientists are employed are employed by the CA Department of Conservation, and are employed by the branches of the University of California marine research programs.

US Geological Survey (USGS)
Fish & Wildlife Service (FWS)
National Park Service (NPS)
National Atmospheric and Space Administration (NASA)
Department of Agriculture (DOA)
Department of Defense (DOD)
Department of Energy (DOE)
Environmental Protection Agency (EPA)
Center For Disease Control (CDC)


Define science, scientific methods. observation, hypothesis, fact, theory, and scientific law.

The Scientific Method

The Scientific Method is how scientific ideas are tested and validated. It involves:
• Collection of data and observations leads to multiple hypotheses (educated guesses).
• Each hypothesis is rigorously tested and it fails (rejected) or passes (and become a theory).
• Tests/experiments must be thoroughly researched and accurately reported.
• Tests/experiments result must be reproducible.

Define science, observation, hypothesis, fact, theory, scientific law, and scientific methods.

is the systematic knowledge of the physical or material world gained through observation and experimentation. The overall goal of science is to understand how the natural world works. The fundamental assumption of science is that the natural world behaves in a consistent and predictable manner.

The scientific method involves the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to demonstrate the truth or falseness of the hypothesis, and a conclusion that validates or modifies the hypothesis.

Observation is the act of noting and recording something, such as a phenomenon, with instruments, in order to gain information. An example is the collection for data for temperature, oxygen levels, and pollutants in seawater at different depths in a harbor to monitor water quality for sea life protection.

A fact is knowledge or information based on real occurrences; something demonstrated to exist or known to have existed.

A hypothesis is a tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation. An example of the testable hypotheses: Observed high levels of certain types of bacteria in seawater samples from a harbor might be linked to an influx of raw sewage leaking from a nearby sewage treatment facility.

A theory is a set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena. Note that in science the word THEORY means something far more certain and concrete than the popular use of the word, which we can define as an assumption based on limited information. Established scientific theories are based on vast amounts of information and knowledge, giving us high confidence that they are correct.

Data: Grades vs. Attendance
Try out the Scientific Method! (A very valuable start to a college course!)

Use the scientific method to evaluate the data on this table comparing two variable factors: student attendance (number of classes missed in an introductory science class) compared with final grades of students in three classes. Discuss observations, facts, hypotheses, and theories. How can these hypotheses be tested? What other factors not listed might explain observable facts?

What would it take to make these hypotheses into a proven theory?
Fig. 1-2. Data: Attendance vs. Grade


2. Matter and Energy (basic concepts)

Basic concepts of chemistry are essential to understanding the physical and chemical properties of matter, particularly 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, and other physical and chemical conditions.

Basic chemistry concepts needed to be understood for this oceanography course include:
* All matter is made up of atoms, and atoms are made up of atomic particles (electrons, protons, and neutrons. An atom is the smallest unit of a chemical element. Atoms have a nucleus composed of neutrons & protons and has a positive charge. Negatively charged electrons orbit around the nucleus in shell-like layers.
* A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Elements have equal balance in numbers of positively charged protons and negatively charged electrons. Common examples of elements are iron, copper, silver, gold, hydrogen, carbon, nitrogen, and oxygen.
* An element is a substance that cannot be broken down into simpler substances by chemical means.
* An element is composed of atoms that have the same atomic number, that is, each atom has the same number of protons in its nucleus as all other atoms of that element.
* The Periodic Table is a list of known chemical elements arranged in order from smallest to largest and by group chemical properties. It is a list of 108 known elements arrange by atomic number. Of these, 92 are naturally occurring (prior to development of artificial nuclear research and development). The lightest element, hydrogen, has one proton, whereas the heaviest naturally occurring element, uranium, has 92 protons. In general elements on the left side of the periodic table are metals, and elements on the right (shown in blue in Figure 1-15) are nonmetals.
* Atoms bond together to form molecules. A molecule is a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.
* A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together in a defined spatial arrangement by chemical bonds. All minerals are chemical compounds, but by comparison relatively few compounds are naturally occurring minerals!
* Types of molecular bonds include metallic (for metals), ionic (compounds that dissolve easily), covalent (most others).
* A mixture is a combination of two or more pure substances in which each pure substance retains its individual chemical properties. Examples of mixtures include rocks, magma (molten rock) air, and seawater.
* Chemical formulas are used to describe compounds such as H2O (for water), NaCl (for salt), CO2 (for carbon dioxide)

The most abundant elements in our physical environment are: H, C, N, O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Fe (Be prepared to name these elemental symbols! -- see Figure 1-4.)

These elements are:
* ingredients of common rocks and sediments (solids)
* components of seawater and air (liquids & gases)
* essential nutrients for life (organic compounds)

An atom of lithium is composed of a nucleus with 3 protons and several nuetron, and surrounded by a cloud of 3 spinning electrons
Fig. 1-3
. Atoms are composed of protons, neutrons, and electrons.Periodic Table
Fig. 1-4.
The periodic table of the elements is an arrangement of the elements based on atomic number (number of protons in an atom).


Chemical Bonds

Molecular compounds are held together on an atomic level by chemical bonds. Three types of chemical bonds include ionic bonds, metallic bonds, and covalent bonds. The types of chemical bond influence the physical properties of the molecular compounds they form.

Molecular compounds held together by ionic bonds are salts. An ionic bond is a chemical bond between two oppositely charged ions. Typically, metals lose valence electrons (loose electrons in their outer shell of orbiting electrons) to become positively charged cations, whereas the nonmetal accepts electrons to become negatively charged anions. For example, common salt (NaCl) has ionic bonds between sodium (Na+) has a positive charge and chlorine (Cl-) has a negative charge. Salts readily dissolve in water as their charged ions are attracted to parts of water molecules that can also have positive and negative charges. As water evaporates, the ions dissolved in water will precipitate again as salts. Natural salts like halite (NaCl) and gypsum (CaSO4) are generally soft minerals and can dissolve in water.

Metals are held together by metallic bonds. Compounds with metallic bonds transmit electricity. With metallic bonds, the valence electrons disassociated from orbiting a single atom and become more of a cloud electrons that surround the positively charged nuclei of interacting metallic ions. Metalloids are intermediate between those of metals and solid nonmetals. Although most elements are metals (all those on the left and center parts of the Periodic Table), only a few elements occur naturally in metallic form including gold, platinum, copper, iron, and mercury (in liquid form). Some minerals are metalloid compounds including pyrite (FeS2), magnetite (Fe3O4), and galena (PbS) (Figure 1-7).

Molecular compounds held together by covalent bonds are non-metallic compounds. Covalent bonds occur when two or more atoms share orbiting electrons, creating more stability in the valence shell of electrons between the bonding elements. These materials can form crystal complexes and do not transmit electricity and tend to be harder, more durable compounds. For instance, most gem minerals are non-metallic compounds with covalent bonds. The mineral quartz (SiO2) is a non-metallic crystalline compound (see Figure 1-8).

Van der Waals forces (bonds) are weak, nonspecific forces between molecules and include attractions and repulsions between atoms, molecules, and surfaces. Van der Waals forces are responsible for friction and what makes water “sticky.”

Salt dissolves in and precipitates from water
Fig. 1-5.
Salt crystals are held together by ionic bonds. Salt compounds dissolve in and precipitate from water.

Salt deposits in Death Valley
Fig. 1-6.
This view shows salt crystals precipitating on a dry lakebed in Death Valley, California.

Metals (native copper and gold), magnetite and pyrite
Fig. 1-7.
Metallic bonds occur in metallic minerals (like native copper and gold) and metalloid minerals (like magnetite and pyrite).
Quartz crystal
Fig. 1-8.
Most minerals are non-metallic crystalline compounds held together by covalent bonds (and will not transmit electricity). [This mineral sample is quartz.]


Isotopes (and Radioactivity)

Many elements have one or more isotopes. Isotopes are of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties. Some isotopes are not stable and ultimately break down or change into other elements. We call such isotopes radioactive. Many elements have both stable and radioactive isotopes. For example, the element carbon has 3 isotopes: 12C and 13C are stable, whereas 14C is unstable and will undergo radioactive decay. All there isotopes have 6 protons, but have 6, 7, and 8 neutrons, respectively.

In the natural environment there are 80 different elements that have one or more isotopes. Of these, at least 254 stable isotopes that have never been observed to decay. Another 50 are radioactive. With the invention of nuclear weapons, and the numerous nuclear bomb test through the 1950s to the present, there are now many more radioactive isotopes loose in the environment. The mixing of these radionuclides in the air, water, and sediments dilute their concentrations, but also disperse them to all regions of the world.

For example, the March 2011 Fukushima Daiichi nuclear disaster associated with the massive earthquake and tsunami in Japan released large amounts of radiation into the marine environment.


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. All physical and chemical reactions involve either the loss or gain of some form of energy.

Electromagnetic energy
from the Sun is the force behind all motion of the atmosphere and the oceans. The Sun's electromagnetic energy comes from nuclear fusion in the Sun's core. The immense pressure in the Sun's core fuses hydrogen atoms into helium atoms, a process that gives off vast amounts of energy and causes the Sun and other stars to glow. Geothermal energy is the driving force for motion within the planet (including plate tectonics, earthquakes, and volcanoes). Both solar electromagnetic energy and geothermal energy are utilized to support life and ecosystems within the marine environment.

Electromagnetic radiation are forms of energy that can be emitted or reflected from objects through electrical or magnetic waves traveling through space. The electromagnetic spectrum describes the different forms of electromagnetic radiation ranging from low frequencies with long wavelengths (such as radio waves) to very short wavelength, high energy gamma rays (Figure 110). The shorter the wavelength, the greater the amount of energy is transferred by an electromagnetic wave.All natural materials either transmit, reflect, or absorb electromagnetic energy in different ways. Solar energy that is absorbed by the atmosphere, oceans, and land is converted to heat or other energy forms. An equivalent amount of energy is radiated back into space. Some of the energy is used to move the oceans and atmosphere, and support life in the process over time.

Radioactivity measured with a geiger counter
Fig. 1-9. Radioactive
elements that occur in rocks and minerals include isotopes of potassium, thorium, radium, and uranium. and may display measurable radioactivity. A geiger counter us used to measure materials for radioactivity.

The electromagnetic spectrum
Fig 1-10.
The electromagnetic spectrum is the range of wavelengths or frequencies over which electromagnetic radiation extends.


Mass and Density

Mass is the property of matter that measures its resistance to acceleration. Roughly, the mass of an object is a measure of the number of atoms in it. Mass is often confused with weight. Weight is a measure of an amount of mass under the influence of gravity. For instance, a 150 pound person on Earth would only weigh 25 pounds on the moon because the Moon only has 1/6 the gravity of Earth.

Density is the ratio between mass and volume. It is a measure of how much matter an object has in a unit volume (such as cubic meter or cubic centimeter).

Density = mass/volume
• Usually defined in grams per cubic centimeter - gm/cm3

Density Stratification
• The earth and oceans have layers based upon density differences, they are density stratified.

Examples of the density of earth materials
• Air ~0.1 gm/cm3
• Freshwater 1.0 gm/cm3
• Saltwater ~1.001-1.03 gm/cm3
• Surface rocks ~3 gm/cm3
• Center of earth ~16 gm/cm3

Calculate the change in density when we add 1% salt to freshwater:

(.99)(1.0 gm/cm3) + (0.01)(3.0 gm/cm3) = 1.02 gm/cm3
Seawater has an average density of 1.027 gm/cm3, but this varies with temperature and salinity over a range of about 1.020 to 1.029.


Early Contributions to Earth Science and Astronomy

Records of astronomical observations and cosmological interpretations are known from antiquity, including from ancient Egyptian, Greek, Chinese, Roman, Muslim, and other cultures. Early cultures used astronomical observations for practical purposes, using the Sun, Moon, stars, and planets for the basis of calendars, clocks, and navigational guides. However, without the knowledge available to the world today, interpretations of much that was observed was inferred through the filter of religious and political ideologies.

Aristotle, Copernicus and Galileo

One of the oldest records concerning the origin of the Earth and basic geologic concepts are attributed to Aristotle in the 4th Century BC who made critical observations the slow rate of physical processes changing the landscape. He noted that changes took place at rates much slower than can be observed in a single life time. Although rather simplistic, Ancient Greek philosophy observed the material world consisting of 5 elements that included earth, air, fire (plasma), water, and “aether” (an unobservable unknown force), and that interactions between these material forces accounted for all that was observable in the world (Figure 1-11).

In the 16th Century, Copernicus was the first to explain the observed "retrograde, looping" phenomena of planet motion by replacing previously held ideas of geocentrism (Earth being the center of the Universe) with heliocentrsm (the Sun being the center of the observable Universe of his times).

Italian physicist and astronomer, Galileo Galilei (1564-1642) used an early telescope and discovered four large moons of Jupiter (Figure 1-12). He promoted the theory that the sun, not the Earth, was the center of our Solar System. In 1615 he was subjected to the Roman Inquisition for his scientific inquiries. He was forced to publicly recant his beliefs and subjected to house arrest for the remainder of his life. (Note that the Roman Catholic Church eventually accepted his theory and officially forgave him in 1992!)

Lava flowing into the sea in Hawaii
Fig. 1-11.
Lava flowing into the sea illustrates the Aristotelian material elements of "earth, wind, fire, and water."
Painting of Galileo Galilai
Fig. 1-12. Galileo Galilei first used a telescope to examine the night sky.


Gravity is a force that attracts a physical body toward the center of the Earth, or toward any other physical body toward any other body having mass. Gravity is a accelerating force, meaning that it's effects are similar to a measurable change in velocity. On the earth surface, the average rate of gravitational acceleration is an increase of about 9.8 meters per second per second (m/sec2).

Understanding the very mysterious force of gravity is fundamental to characterizing the mechanics of the orbits of planets and moons within the Solar System (and objects moving throughout the universe). Using research by earlier astronomers, between 1609 and 1619, Johannes Kepler presented scientific laws that describe to character of the elliptical motion of planets around the sun. Isaac Newton used Kepler's laws to mathematically resolve the nature of gravity which he presented in 1687 as his "law of universal gravitation" which states "a particle attracts every other particle in the universe using a force that is directly proportional to the product of their masses, and inversely proportional to the square of the distance between them" (Figure 1-13). Gravity is a weak but measurable force, but becomes observable when dealing with objects on the scale of moons, planets, and satellites launched into space.
Newton's law of universal gravitation illustrated.
Fig. 1-13. Newton's Law of Universal Gravitation.

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 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 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 notions that the Earth being "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 (Leonardo Da Vinci believed fossils were ancient life forms, older that 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.

Stratigraphy is a branch of geology concerned with the systematic study of bedded rock layers and their relations in time and the study of fossils and their locations in a sequence of bedded rocks. A stratum is a bed or layer of sedimentary rock having approximately the same composition throughout (plural is strata) (Figure 1-14).

A Scottish physician, James Hutton (1726-1797) studied rocks and landscapes throughout the British Isles and promoted "uniformitarianism." Uniformitarianism theory implies that all geologic phenomena may be explained as the result of existing forces having operated uniformly from the origin of the earth to the present time. Uniformitarianism is commonly summarized: "The present is key to the past."

Hutton fearlessly debated that the Earth was very old, measured in millions of years rather than thousands of years as promoted by the religion organizations of his times. Many scientists of his time promoted a theory of catastrophism.
Catastrophism theory implies that major changes in the earth's crust result from catastrophes rather than evolutionary processes. The theory of catastrophism was more in line with religious doctrine common in the 17th and 18th centuries.

It is interesting that today, uniformitarianism still applies to most geologic and landscape features, but discoveries have show that the Earth, or large regions of it, have experience great "catastrophes," such as asteroid impacts, great earthquakes, super storms, great floods, or volcanic events. However, these events can be scientifically viewed within the greater context of modern geology. Uniformitarianism explains how observable processes taking place over long periods of time can change the landscape. Examples include:

  • earthquakes only happen occasionally, but 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 "mapable" (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 1-15 and 1-16).

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 1-17). As nations began to understand the importance of geologic mapping for evaluating their natural resources, the science of 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 term geological time is used to describe the time of the physical formation and development of the Earth (especially prior to human history). Geologic time also applies to the age and history of the Universe. Geologic time is an essential component in discussions relating to the evolution of life on Earth (Earth history and evolution are the focus of Chapter 2).

The geologic time scale is a chart that geologists have subdivided periods in Earth's history is measured periods spanning millions to billions of years. Segments of time periods have been named to help define the chronology of events (such as formation of mountain ranges), the formation of rock units (such as the age of a lava flow), the age of fossils, organizing geologic map units, and other purposes. Below is a standard geologic time scale listing names of major time periods with time span information.

The geologic time scale used today has evolved through the past two centuries as new scientific discoveries have been made and new technologies for dating the age of earth materials have become available. The most recent version of the geologic time scale is released on a Geological Society of America website as updated versions become available.

The primary arguments about the age of the Earth and the observable Universe have been resolved by the global scientific community, but paradigms have ways of shifting as new discoveries are made and new information becomes available, and those ideas are tested by scientific methods. Vast periods of time in Earth history are fundamental parts of understanding biological evolution of life on earth (paleontology), understanding genetics, particularly related to human evolution, and in astronomy explaining the vastness and age of the observable universe. Geologists have subdivided periods in Earth's history is measured periods spanning millions to billions of years. Segments of time periods have been named to help define the chronology of events (such as the uplift of mountain ranges), the formation of rock units (such as the age of a lava flow), the age of fossils, etc. Names of geologic time periods (like "Late Cretaceous" or "Pleistocene") are used for organizing geologic map units, charting the age or petroleum-bearing rock layers underground, and perhaps hundreds of other purposes.

The current age of the earth accepted by the majority of the scientific community is approximate 4.56 billion years.

It can be argued that all the science and discoveries of geology didn't matter much to the average citizen of the world until the discovery of the Spindletop Oil Field in 1901 (Figure 1-18). It was this discovery in Texas that started the modern Petroleum Industry. This happened the year before Henry Ford started his automobile company using internal combustion engines. This events initiated the growth and expansion of the world largest and most profitable industry—Big Oil. The demand for oil and mineral resources over the following century created opportunities for hundreds of thousands of people to be employed as geoscientists. However, the environmental impacts associated with consumption of fossil fuels (coal, oil, and gas) is now a paramount topic of conflicting discussion of needs and demands for energy to power modern society and and the long-term implications for climate change around the world.

The explosion of knowledge gained from the petroleum industry is only part of the story. The discovery of mineral resources, particular gold and other precious metals, as well as large diamond and other gem deposits have created "rushes" and "boom" to "bust" communities around the world. The advertising of the potential of finding gold in California in 1849 lead to one of the greatest human migrations in modern history, even though the amount of gold found in California is small compared with other locations around the world, particularly South Africa.

Strata exposed in the Grand Canyon.
Fig. 1-14. Layers of strata (beds of sedimentary rocks) exposed in the Grand Canyon.

Geologic time scale
Fig. 1-15. 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.

Time Scale ClockFig. 1-116. "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!

William Smith's 1815 map of England, Wales, and parts of Scotland
Fig. 1-17. William Smith's geologic map of 1815
was the first attempt to map an entire country.
(British Museum of Natural History)

The Lukas Gusher started the oil rush to the Spindletop Oil Field in Beaumont, TexasFig. 1-18. 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 1-19).

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 thick magnetic metallic inner core that is overlain by a 1400 mile 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 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).

Structure of the Earth
Fig. 1-19. The internal structure of the Earth is divide into an inner and outer core, a thick mantle, and a thin crust on the surface. Other planets and moons also have cores, mantles and crusts, although they may be very different in composition for Earth.


Earth's Atmosphere (an introduction)

An atmosphere is the gaseous mass or envelope surrounding a celestial body (including the one surrounding the Earth), and retained by the celestial body's gravitational field. (The atmosphere is the focus of Chapter 5.)

The Earth's atmosphere is subdivided into levels (Figure 1-20):

The troposphere is the lowest portion (up to about 6-8 miles) where all weather takes place and contains about 80% of the air's mass and 99% of water vapor.

The overlying stratosphere contains an abundance of ozone which absorbs ultraviolet radiation, protecting life on land and in the shallow ocean extends up to about 31 miles.

The upper atmosphere (mesosphere and thermosphere) extends upward to the transition into space above about 60 miles where the charged atomic particles of the solar wind begins to interact with atmospheric gases.

Fig. 1-20. Structure of the atmosphere.

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 1-21).

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 the regions of the surface, subsurface, and atmosphere of the Earth (and possibly other planets) occupied by living organisms.

Fig. 1-21. The hydrologic cycle is illustrated in this concept diagram.


10. Earth's Place in the Universe

Many aspects of astronomy have contributed to the knowledge of the origin and geologic history of planet Earth. Meteorites have been found, collected, and studied for centuries. Telescopes on the ground and now in space, satellites, robotic and manned missions to space, the Moon, and other planets and moons in our Solar System objects have greatly expanded the collective knowledge about the origin of our planet and objects in the Solar System—all of which have evolved to their current state over billions of year. So far, life is only known to exist on Earth, but it could possibly exist elsewhere, even within our Solar System. We just haven't proven it yet.

Discoveries Leading To Modern Astronomy

The ancient Greek, Roman, and Muslim astronomers followed the geocentric model (or Ptolemaic system) that described the universe with the Earth at its center. The geocentric model wasn't seriously challenged until Nicolas Copernicus who published a report in 1543 suggesting that the sun, not the Earth, was the center of the Universe (called Copernican heliocentrsm). However, the Copernican system was also discovered to be flawed as telescopes were developed to see farther into space and astronomers began to grasp the immense scale of time and distance between our Solar System and other objects in our Milky Way Galaxy and the Universe beyond.

Meteor Crater near Flagstaff, Arizona
Fig. 1-22. Meteor Crater
near Flagstaff, Arizona is a bollide and meteor impact site that happened about 50,000 years ago. Erosion eventually destroy or buries most craters, but many have been found.
Giant redwood in Big Basin State Park, CA
Fig. 1-23.
Like this giant redwood in Big Basin State Park, California, all physical materials, including life on Earth, have an origin connected to the formation of elements from events that happened in space billions of years ago!


Determining the Expanse of space

From the time of Galileo to the beginning of the 20th century, the telescope technology advanced, and the night sky with it stars, planets, gas and dust clouds (nebula), and other objects were charted in great detail. The problem was that we could see lots of stars, but had no way of knowing how far away there were because stars vary in their brightness in addition to their distance. Astronomers have developed several methods to directly or indirectly measure the distance to object is space.

It was in 1923 that Edwin Hubble found dozens of "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 - an obvious band of densely distributed stars and clouds of dust visible as a band in the clear night sky (Figure 1-24). 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.

The milky way stands out in a clear night sky.
Fig. 1-24. The Milky Way as photographed on a clear night sky. The Milky Way is the main plane of of the galaxy where stars are concentrated.


The Andromeda Galaxy is a spiral galaxy (Figure 1-25). 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 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; approximate 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.

Andromeda Galaxy, 2.5 million light years away is visible to the nake eye on autumn nights
Fig. 1-25. Andromeda Galaxy



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 1-26 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 1-27 to 1-24). 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.

A field of possibly hundreds of galaxies in a distant region of the night sky.
Fig. 1-26. A field of galaxies.
A Spiral galxy (NGC 6814)
Fig. 1-27.
A spiral galaxy.
An elliptical galaxy, NGC 3610Fig. 1-28. An elliptical galaxy

An irregular galaxy combining two colliding galaxies NGC 4038 and NGC 4039
Fig. 1-29. An irregular galaxy


Earth's Place in the Observable Universe (Figure 1-30)

* The Moon revolves around the Earth every 27.32 days.
* The Earth-Moon System revolves around the Sun every 365.242 days (1 year).
* It takes the Sun about 230 million years to make one complete orbit around the center of our Milky Way Galaxy (traveling about 828,000 km/hr). Our galaxy is about 100,000 to 120,000 light-years in diameter and contains over 200 billion stars. Our Solar System resides roughly 27,000 light-years away from the Galactic Center.
* The Observable Universe is the part of the universe that can be observed by the naked eye or by modern telescopic methods. The light we observe from object in space has travel great distances (measured in light years). This means that distant objects in deep space we see on Earth today have long since changed or moved.

Observable Universe
Fig. 1-30. Earth's place in the Observable Universe.


The Big Bang Theory

In the 1927, a French astronomer, Georges Lemaître, proposed the idea that in the distant past that the Universe started as just a single point in space, and as the Universe has been expanded as a great explosion to what is observable now. Two years later in 1929, Edwin Hubble reported that the most distant observable galaxies are moving away at a faster rate than ones closer to Earth. This observation, and much other evidence, now supports a 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 1-31). 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.

Brief story of the Big Bang
Fig. 1-31.
A very brief story of the Big Bang and the evolution of the Observable Universe over an estimated 13.8 billion years.



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 1-32). 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 1-33). Many stars are clustered together, often sharing a common stellar history (Figure 1-34). Some stars orbit each other relatively close to one another as binary systems (Figure 1-35). 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 1-36). 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 1-37).

Life Cycle of Stars

Stars form in giant molecular clouds called nebula. 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 1-38 to 1-43). Nebulae are the birth place of stars and solar systems. Nebula can form from the explosion of stars at the end of their life cycle.

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). 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. 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 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.

A constellation chart of stars visible in the fall night skyFig. 1-32. A constellation chart of stars visible in the fall night sky.

Colorful stars in a massive cluster in the Omega Centari region. Fig. 1-33. 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.

The Pleiades star cluster Fig. 1-34. 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.

The Albiero binary star systemFig. 1-35. Albireo is the name of a binary star system visible about 380 light years distant.

The Hertzspring_Russel Diagram of star classification Fig. 1-36. The Hertzsprung-Russell Diagram illustrates classification of stars based on star size, temperature, and intensity. The life cycle of stars depends primarily on their mass and composition. Illustration of the life cycle of stars.
Fig. 1-37. Illustration of the life cycle of stars from their formation in nebulae to their ultimate fate of collapsing and exploding to form white dwarfs, neutron stars, or black holes, depending on their mass.
Nebula Carena
Fig. 1-38. Carina Nebula
, a part of our Milky Way Galaxy where new stars are forming and emerging from a gas and dust cloud in what is commonly called a "stellar nursery."
Fig. 1-39. Supernovas
are great explosions that partially to completely demolish aging massive stars, releasing new matter and gas to create a new generation of stars in newly created nebula.

The Horsehead NebulaFig. 1-40. The Horsehead Nebula, located in the constellation Orion, is , mostly dust. Bright spots in the nebula are associated with newly forming stars. The Crab Nebula Fig. 1-41.The Crab Nebula is the remnant of a supernova recorded in 1054 A.D. The Crab Nebula now spans about 10 light years and has a neutron star at its center. The Ring Nebula
Fig. 1-42. The Ring Nebula is located about 2,000 light years from Earth. The nebula is a gas shroud about a light year in diameter that surround a dying star.
The Hour Glass nebula
Fig. 1-43. The Hour Glass Nebula (discovered by the Hubble Telescope) is an unusual young planetary nebula located about 8,000 light years away.


The Solar System

The Solar System is the system containing the Sun and the bodies held in its gravitational field, including the planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune), planetary moons, the asteroids, comets, and other interstellar bodies and matter (Figure 1-44).

Most planets and planet systems (planets with orbiting moons) orbit the Sun in the ecliptic plane—an imaginary plain containing the Earth's and other planets' orbit around the Sun.

Our Solar System
Fig. 1-44.
Our Solar System originated from gas, dust, and other matter that gravity pulled together in a stellar nebula about 5 billion years ago.


The Sun

The Sun is the star at the heart of our Solar System (Figure 1-45). The sun's intense solar energy and gravity influences the planets throughout the Solar System and beyond. Facts about the Sun include:

* By mass, the Sun is composed of hydrogen (70.6%) and helium (27.4%), all other elements are trace by comparison.

* The Sun's average diameter is about 864,000 miles (about 109 times the size of Earth).

The Sun' mass is about 333,000 times the mass of Earth. The average density of the Sun is 1.409 grams/cm3 (compared with Earth which is 5.51 grams/cm3).

* The Sun rotates on its axis in an unusual way. The rotation period at the Sun's equator is about 27 days, but is about 36 days at it poles.

Fig. 1-45. The Sun
(our star), is one of billions of stars in our Milky Way Galaxy.

Structure of the Sun

The Sun's internal structure is inferred to be subdivided into several zones (Figure 1-46).

* Core—The internal temperature of the Sun's is estimated to be about 27 million degrees Fahrenheit, hot enough to drive the nuclear fusion process of converting elemental hydrogen into helium, the source of solar energy.

* Radiative zone—Above the core where fusion occurs, slowly radiates upward through the massive radiative zone.

* Convection zone—The temperature is estimated to drop to about 3.5 million degrees Fahrenheit, where convection of "great bubbles of dense plasma (ionized matter) rise toward the surface in a convective manner (like a pot of boiling soup).

* Photosphere—A 300 mile thick layer of hot gas makes up the surface of the Sun where most of the Sun's energy radiates into space. The Sun's surface temperature is about 10,000 degrees Fahrenheit, hot enough to radiate solar energy in the visible light spectrum.

* Chromosphere and Corona—The outermost layer of the sun is a thin solar atmosphere (the chromosphere) which extends as streaming plasma deep into space (the corona). The region is not a hot as the underlying photosphere, but is heavily influence by magnetic forces generated deeper in the Sun. Features of the chromosphere are only visible with special sun-observing telescopes. However, the corona is visible during solar eclipses when the disk of the Moon's shadow temporarily blocks the intense light form the photosphere (Figure 1-47).

Internal structure of the Sun.
Fig. 1-46. Internal structure of the Sun.

The Sun's corona is visible during a solar eclipse. Fig. 1-47. 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 1-48 and 1-49). 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 1-45 and 1-46).

Sunspotes are dark spots on the Sun's surface.Fig. 1-48. Sunspots appear as dark splotches on the Sun's surface. Comparison of the relative size of sunspots to the size of the Earth.Fig. 1-49. Comparison of the relative size of sunspots to the size of the Earth. A solar flare erupting on the Sun;s surfaceFig. 1-50. A solar flare erupting on the Sun's surface. A large solar prominence erupting on the Sun's surfaceFig. 1-51. A large solar prominence erupting on the Sun's surface.


The Solar Wind

The solar wind is a stream of energized, charged particles (mostly electrons and protons) flowing outward from the Sun's upper atmosphere. The ionized particles are released into space from the Sun's corona and by solar mass ejections (prominences and flares). The solar wind moves through solar system at speeds roughly 500 miles per second (800 km/sec); about 10 days from Sun to Earth) and can reach temperatures of about 1 million degrees (Celsius). The solar wind is what blows a "tail" away from the bodies of comets as they go through the solar system. Estimates suggest the Sun loses the equivalent of “one Earth mass” about every 150 million years (which isn't much considering the size of the Sun). Large corona ejections from the Sun’s surface result in solar storms that frequently impact Earth and other planets.

The Earth’s magnetic field shields the planet from the erosive effects of the solar wind (Figure 1-52). Particles trapped by Earth’s magnetic field flow into the upper atmosphere producing the aurora borealis (Northern Lights) and aurora australis (Southern Lights) (Figure 1-53). Over geologic time, the solar wind also erodes the atmosphere of planets with weak magnetic fields (this includes Mercury, Mars, and the Moon). Strong auroras have been observed on the gas planets (Jupiter, Saturn, Uranus, and Neptune)—all of which have a dense atmosphere and a strong magnetic field.

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.

Coronal mass ejections result in the solar wind which is deflected and captured by the Earth's magnetic field.Fig. 1-52. Coronal mass ejections result in the solar wind which is deflected and captured by the Earth's magnetic field.

The aurora borealis are streaming light displays lights in the northern hemisphere.Fig. 1-53. The aurora Borealis are streaming light displays lights in the northern hemisphere.


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, and other objects under the gravitation influence of the Sun.

The 4 inner Rocky Planets

Mercury Venus Earth Mars

Fig. 1-54. Mercury

Fig. 1-55. Venus

Fig. 1-56. Earth

Fig. 1-57. 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 Planetary Systems

Jupiter Saturn Uranus Neptune

Fig. 1-58. Jupiter

Fig. 1-59. Saturn

Fig. 1-60. Uranus

Fig. 1-61. 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 1-62).

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).

Moon Fig. 1-62. The Moon
moon radius:
1,079 miles (1,736 km)
orbital period: 27 days
average distance from Earth: 238,855 miles (383,300 km).
gravity: 1.622 m/s2


Asteroids and Comets

An asteroid is any of the thousands of small irregularly shaped bodies of stone, metal, and ice that revolve about the sun. In our Solar System, asteroids typically range in size from about one-mile (1.6 km) to about 480 miles (775 km) in diameter (Figure 1-63). Most asteroids orbit the Sun in the Asteroid Belt located between Mars and Jupiter. However many large objects have been observed passing through Earth's orbital path. Asteroid collisions with Earth were frequent in Earth's early history, but are now extremely rare events. The extinction of the dinosaurs and many other species is mostly blamed on the environmental catastrophe created by an asteroid impact about 65 million years ago, defining the end of the Cretaceous Period (and Mesozoic Era).

A comet is a celestial body thought to consist chiefly of if ices of ammonia, methane, carbon dioxide, and water, and dust (Figure 1-64). Comets are observed only in that part of its orbit that is relatively close to the sun, having a head consisting of a solid nucleus surrounded by a nebulous cloud of gas and debris (a coma) up to 2.4 million kilometers (1.5 million miles) in diameter. The coma turns into an elongated curved vapor tail arising from the coma when sufficiently close to the sun. There may be more than 100 million comets in the outer Solar System.

A meteor is a bright trail or streak that appears in the sky when a meteoroid is heated to incandescence by friction with the earth's atmosphere.

A meteorite is a stony or metallic mass of matter that has fallen to the Earth's surface from outer space (Figure 1-65).
Fig. 1-63. Asteroids are solid objects in space consisting mostly of rock, dust, some metals, and possibly ice.
Comet Haley
Fig. 1-64. Comets are like asteroids (mostly frozen gases and ice, dust, some rocky material) that leave a trail of material as they are heated as they approach the sun.
Meteorite with magnet
Fig. 1-65.
An iron-nickel meteorite is magnetic.

Bollide over Oklahoma Panhandle, 9/30/2008
Fig. 1-66. Bolide (meteor fireball) over Oklahoma Panhandle, 9/30 2008
A bolide is a large meteor (or asteroid or comet) that explodes in the atmosphere (Figures 1-66 and 1-67). About a dozen significant (recorded) bolide events happen each year. A recent bollide explosion involved the Chelyabinsk meteor that blew up over Russia on February 15, 2013. The explosion occurred high in the atmosphere, but the atmospheric shock wave blew out windows, doors, and injured over a thousand people on the ground (see YouTube video).

An atrobleme is an eroded remnant of a large crater made by the impact of a comet or asteroid (large meteorite). Because of weathering and erosion processes, impact craters are relatively "short lived" on the Earth's surface (with exceptions for large impacts or in arid regions). Currently there are almost 200 known craters distributed on all continents. Others have been discovered by oil drilling through sedimentary cover.
Bollide events during period 1994 to 2013
Can you explain why are there so many craters on the surface of the Moon but not on surface of the Earth? Fig. 1-67. Map of reported bolide events 1994-2013.


The Outer Solar System

The region beyond to orbit of Neptune is called the Kuiper Belt. It is the circumstellar disc at the outer margin of the Solar System beyond the planets. It is similar to the Asteroid Belt, but far larger (wider) and many times more massive. The belt extends from Neptune (at about 30 AU [astronomical units] to about 50 AU - one AU is the average distance of the center of the Earth to the center of the Sun.

There are more than 100,000 Kuiper Belt Objects (KBO). The Kuiper Belt includes three recognized planetesimals (or dwarf planets) including Pluto, Haumea, and Makmake. KBOs are probably mostly composed of frozen volatile compounds (ices of methane, ammonia, and water). (Pluto's status as a 'planet" has been argued for years - Figure 1-63. (Pluto does not behave like other planets; it does not orbit the Sun within the ecliptic plane, and sometimes Pluto's orbit puts it closer to the sun than Neptune.)

Beyond the Kuiper Belt is the hypothetical Oort Cloud - a region that may contain an abundance of icy planetesimals and objects that may surround the Solar System at a distance of between 50,00 and 200,000 AU. The Oort Cloud may be the source of most of the long-period comets that have been observed.

Fig. 1-68. Pluto
- "formerly a planet," now it is called a "planetesimal," or a "dwarf planet" in the Kuiper Belt. Pluto has 5 moons.


Nebular Hypothesis of the Origin of the Solar System

Many billions of years before the formation of the Solar System there were probably several generations of star formation and destruction occurred in our region of the Milky Way. Ancient supernova explosions in the distant past produced the elements we observe in our Solar System today (an example of a fairly recent supernova explosion is shown in Figure 1-69). Nuclear fusion in stars coverts hydrogen into helium and other elements up to the atomic mass of iron. Elements heavier than iron are only created by intense energy in supernova explosions. Gas, dust, and other matter from previous supernova explosions became part of a nebula (Figures 1-70). Gravity gradually condenses material in nebulas into new star systems (see example in Figure 1-71).

An ancient nebula in the Milky Way Galaxy was the birthplace of our Sun and Solar System. Currents of material (gases, dust, asteroids, etc.) under the influence of gravity consolidated into the proto-suns and proto-planets of new star systems within the nebula, one of which became our Sun and Solar System. Because all matter is influenced by gravity, matter within nebulas gradually is pulled toward areas with more matter. As matter moves toward a location with greater density it may be caught in a spinning current around a center of accumulating matter that may become a sun or a planet.
• The combination of gravity and spin results in the formation of a flat, disk-shaped stellar cloud with the Proto Sun (pre-sun) at the center. The increasing mass and gravity of the Sun grabs most of the matter in the evolving Solar System (Figure 1-72).
• The Sun eventually gains enough mass that nuclear fusion can begin, creating the intense energy that it radiates into space.
• The massive release of energy from the new Sun heats the surrounding stellar region, combined with the force of high energy plasma (the solar wind) pushes the light elements (mostly hydrogen and helium) out of the inner Solar System region. As a result:
• Inner planets form from the accumulation mostly of metallic and rocky substances (dust). Lighter gas materials are pushed to the outer regions of the Solar System.
• Larger planets in the outer part of the Solar System began forming from gasses (mostly hydrogen) and fragments of ice (H2O, CO2, and other gases).

• The Sun and its Solar System gradually formed by the gravitational attraction of materials within a stellar nebula beginning almost 5 billion years ago.
• The evolving Solar System assumes a flat, disk shape of condensing gases and dust with the Proto Sun (or pre-Sun) at the center. The consolidation of matter under gravitational attraction causes the surrounding nebular cloud to flatten and spin.
• After "solar ignition" Early, the Sun's intense solar energy and solar wind begins to drive gases away from the inner Solar System.
• Inner planets begin to form from metallic and rocky substances (dust).
• Larger outer planets began forming from fragments of ice (H2O, CO2, and others).

Proto-Earth formed

Studies of meteorites and samples from the Moon suggest that the Sun and our Solar System (including proto-planets) condensed and formed in a nebula about 4.55 billion years ago. Currently, the oldest samples of "Early Earth" rock samples from the Jack Hills region of Australia that contain crystals of the mineral zircon dated to an age of about 4.4 billion years. A recent Scientific American article places the current assumed age of the Earth is about 4.56 billion years old.

Earth also formed through gravitational attraction of interstellar dust, gases, small asteroids and larger objects (planetesimals) within the early Solar System consolidating within the Sun's stellar nebula and within its orbital belt around the Sun.
• Initially, the Earth was probably homogenous in composition, eventually becoming extremely hot and mostly molten within.
• Proto-Earth was probably under constant bombardment by asteroids, comets, and planetary dusts and debris.
• Current thought is that the Proto-Earth grew to a larger in size than today’s Earth.

Formation of the Earth-Moon System

Proto-Earth experienced a great planetary collision resulting in formation of the Moon.

Studies of the rocks brought back from the Apollo Missions show that the Earth and Moon have similar mineral and isotopic compositions. Such an impact probably vaporized much of the upper portion of the Proto-Earth, throwing much of it into space. Gravity eventually consolidated the material into the Earth-Moon system. This, and the fact that the Earth has a tilted axis, and the Moon's orbit is not in the ecliptic plane, suggest that the Moon may have formed from the collision of another small planet-sized object with the Earth early in the history of the Solar System (Figure 1-73). It is this tilt to Earth's axis that gives rise to the seasons as it orbits the sun.

The Moon's surface displays a heavily cratered surface, many of the craters are massive in scale. Dark-colored "maria" are regions on the lunar surface where molten material flooded the surface, filling in depressions created by massive impacts. The lighter-colored highland regions are rugged mountainous regions consisting of heavily cratered moonscapes and tectonic features that formed early in the Moon's history when the mantle was more molten and lighter material floated to the surface to crystallize and form the lunar crust. The cratering was a result of asteroids and comets collisions, mostly within the first billion years of the Moon's history.

Fig. 1-69. Supernovas
are great explosions that partial to complete demolish aging stars, releasing new matter and gas to create a new generation of stars.
Fig. 1-70. Nebula
, the birthplace of stars; some are formed from the explosion of other more ancient stars, some thousands to millions time larger than the Sun.
Nebula Carena
Fig. 1-71. Pillars of Creation
, a part of Eagle Nebula in our Milky Way Galaxy where new stars are forming and emerging from a gas and dust cloud—a stellar nursery.
Evolution of the Solar System.
Fig. 1-72. A brief explanation of how the Solar System came to be through the process of stellar evolution.
Earth collides with another planetessimal, forming the Earth Moon system.
Fig. 1-73. Proto Earth colliding with another object


Evolution of Earth’s Layered Structure

Earth has a layered structure, having an outer rocky crust and mantle overlying a molten and solid metal core, however, this internal layered arrangement did not exist early in Earth's history (Figure 1-74).

• Early in Earth's history the composition of the planet was probably more homogeneous. However, just like oil and water don't mix, metals separated from non-metal substances, and as metals are denser, gravitation forced them to sink toward the planet's core.
• Likewise, molten material rich in dissolved gases and lighter silica-rich matter is less dense and over time it gradually migrated upward accumulating in the mantle and thin crust where some of it reached the surface, resulting in volcanism and massive degassing.
• Despite intense asteroid bombardment, early crust began to form.
• Chemical segregation under the influence of gravity established the basic divisions of Earth’s interior (core, mantle, and crust). This process also happened with other planets, moons, and planetesimals in the Solar System.

The structure of the Earth is discussed in detail in Chapters 3 and 4.
Formation of Early Earth and its layered internal structure.
Fig. 1-74. Formation of the early Earth and the eventual development of its internal layered structure: core, mantle, and crust. Volcanic degassing and accumulating gases from space led to the formation of Earth's atmosphere and oceans.


Origin of Earth's Atmosphere and Oceans

The study of meteorites and material in space suggest the the early Earth probably had large quantities of water, organic compounds, and other gases trapped in the accumulating material forming the planet. As a result, as rocks melted large amounts of volcanic outgassing took place. This volcanic outgassing contributed to the atmosphere forming around the planet. Volcanic outgassing from the Earth's interior is still taking place as illustrated by gas emissions from volcanic eruptions such as those on Hawaii or on Iceland where the source of molten material is known to be rising to the surface from the mantle (Figure 1-75).
• Current thought is tat large volumes of water vapor and carbon dioxide formed Earth's primitive atmosphere. The atmosphere was also rich in nitrogen, methane, and ammonia.

• Early in Earth history the Earth probably had a thick, hot atmosphere. The surface of the planet was probably hotter than the boiling point of water, so much of the planet's water was trapped as water vapor in the atmosphere.
• Early on, no continents or oceans probably existed (at least no trace of them are preserved from that time), and no evidence of life on Proto-Earth has been discovered.
• Eventually the surface cooled enough for early crust to began to form. With a solid crust and reduced surface temperatures, rainfall could begin to accumulate in depression on the surface. As more and more water was released from the atmosphere oceans began to form.
By about 4 billion years ago (BYA) the Earth's oceans were essentially in place. Oldest rocks from Canada are of this age.
Nearly 2 billion years ago, life had advance enough for photosynthesis to take place, gradually consuming the vast reservoirs of carbon dioxide in the atmosphere and dissolved in the oceans, while releasing oxygen to accumulate in the atmosphere (discussed in Chapter 2).

A volcanic eruption on Hawaii's Kilauea Volcano in Hawaii illustrates that degassing of the Earth's interior is still occurring.
Fig. 1-75. Volcanic outgassing of the interior of the planet is still taking place, as illustrated by volcanic eruptions on Hawaii.


Water and Oceans On Other Planets and Moons

Water is known to exist throughout the Solar System and beyond. However, liquid water is only known on the surface of planet Earth where surface temperatures and atmospheric pressures are in the range where it can remain fluid. Tidal forces between planets and their moons provide a source of energy to keep water in liquid form below the surface of some of the moons in the Solar System.

Both Venus and Mars likely had liquid water oceans early in the evolution of the Solar System, but now Venus is too hot for water to exist, and Mars is too cold and its atmosphere is too thin. Exploration of Mars suggests that liquid water may exist underground and traces may locally flow on the surface, causing erosion, where conditions are right (Figures 1-76).

Europa: Exploration of the Jupiter planetary system suggest that its moon, Europa has an outer crust of solid ice about 10–30 km (6–19 mi) thick which overlies a liquid ocean thought to be about 100 km (60 mi) deep (Figure 1-77). The volume of water in this subterranean ocean is estimated to be more than two times the volume of Earth's oceans!

Ganymede: A subsurface saline ocean is also theorized to exist on Jupiter’s moon Ganymede. Its ocean is estimated to be 100 km deep and lies beneath a crust of ice estimated to be about 150 km thick (Figure 1-78).

Enceladus: Saturn’s moon, Enceladus, is also believed to have a subsurface ocean and NASA’s Cassini spacecraft observed geysers of water erupting from Saturn’s moon, Enceladus during its exploration of the planet system. Spectrographic observations of the geysers also contained traces of salt, carbon dioxide, nitrogen, and hydrocarbons. The moon also has liquid water oceans below its surface, and the geysers appear to be driven by tidal forces between the moon and Saturn (Figure 1-79).

Water planets outside the Solar System: In recent years, astronomers working with powerful telescopes have been finding planets orbiting other stars within our "galactic neighborhood." Although most of these planets are larger than our Earth, some of the planets display evidence of water, possibly oceans.

Venus and Mars
Fig. 1-76. Venus and Mars Fig. 1-77. Europa Fig. 1-78. Ganymede Fig. 1-79. Enceladus

Chapter 1 Quiz Questions 7/17/2017