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Chapter 1 - Introduction to Oceanography

Note to students: This website is a preliminary version of an online textbook for an introductory course in Oceanography at MiraCosta College. Selected links are provided as supplemental reading for information presented in class and during field trips. Note that The content and graphic images presented here are the same used in course lectures (PowerPoint presentations) and will be used on quizzes and exams.
1.1

*** Science involves a language in addition to concepts! So be prepared! ***

What is oceanography?

Oceanography includes the branches of science that deal with the physical and biological properties, and observable phenomena of the world oceans and seas. This oceanography course covers many aspects associated with other disciplines including physical geography, geology (including earth history and astronomy), chemistry, meteorology, biology and ecology. Perhaps most important, human interactions, include general history, exploration, exploitation, and some of the many environmental factors affecting our modern global civilization.

What do ocean scientists do?
* Ocean scientists study all aspects of the marine physical environment (geology, chemistry, biology).
* Oceanographers map the seafloor and work with navigation and remotely sensing ocean basin regions.
* Marine geologists study seafloor rocks and sediments.
* Marine scientists work in environmental fields: climate change, waste management, resource protection.
* Marine engineers work in construction and engineering: archeology, foundations, offshore drilling.
* Marine scientists serve in national security and are involved in public health and safety.
* Marine scientists study coastal erosion hazards, waves, currents, storms.
* Marine biologists study study all aspects of the marine food chain from microbes to megafauna.
* Marine scientist are involved in all forms of shipping, port management, and marine-related industries.
* Ocean scientists in education: schools, parks, museums, and media.

Federal organizations conduct oceanographic research and employ many marine scientists. Note that the abbreviations for these agencies are used throughout this website.
Name and Abbreviation website
National Oceanic and Atmospheric Administration (NOAA) www.noaa.gov
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) www.usgs.gov
Fish & Wildlife Service (FWS) www.fws.gov
National Park Service (NPS) www.nps.gov
National Atmospheric and Space Administration (NASA) www.nasa.gov
Department of Agriculture (DOA) www.usda.gov
Department of Defense (DOD) www.dod.gov
Department of Energy (DOE) www.doe.gov
Environmental Protection Agency (EPA) www.epa.gov
Center For Disease Control (CDC) www.cdc.gov

Click on images for a larger view.

Earth from Space
Fig. 1-1. Earth is an oceans planet!
Map of the Seafloor of the world
Fig. 1-2. Map of the ocean basins of the world.
Monterey BayFig. 1-3. Image of coastal and marine bathymetry and land topography of the central California region showing San Francisco Bay, Monterey Bay and Monterey Canyon offshore.
1.2

The World Oceans (basic geography facts)

• Oceans cover 71% of Earth’s surface.
• Oceans are interconnected (meaning that all water circulates through one world ocean).
• Oceans have huge size and volume (97% of Earth’s water).
The four principal oceans:
Pacific (largest and deepest), Atlantic, Indian, Arctic (smallest and shallowest)
• Plus one: Southern Ocean (or Antarctic Ocean) - extension of oceans around Antarctica below 60° South latitude

Seas are:
• Smaller than true oceans
• Composed of salty water of varying salinity
• Partially or fully enclosed by land. For example the Yellow Sea is connected to the Pacific Ocean and the Red Sea to the Indian Ocean, whereas the Salton Sea and Caspian Sea are fully landlocked.

Selected seas (discussed in this course) include: Mediterranean Sea, Adriatic Sea, Black Sea, South China Sea, Red Sea, Dead Sea, Persian Gulf, Caspian Sea, North Sea, Caribbean Sea, Bering Sea, and Sargasso Sea.
Note there are many other "seas!" In addition, around North America are large oceanic embayments including the Gulf of California, Gulf of Alaska, Gulf of Mexico, and Hudson Bay.



Map of world oceans and Seas
Fig. 1-4. Map of World Oceans and Seas
Ocean Data - Depth and Surface Area
Fig. 1-5. Oceans depth and surface area compared with land.

Comparison of Ocean Basins and Continents

• Average depth about 3688 m (12,100 ft)
• Deepest area of the ocean: Mariana Trench in the Pacific: 11,022 m (36,161 ft)
• Average elevation of continents: 840 m (2,756 ft)
• Highest mountain: Mt. Everest 8850 m (29,935 ft)

See: Volumes of the World's Oceans (NOAA)


Topography is the measurement of the elevation on land. Bathymetry is the measurement of depth of water in oceans, seas, or lakes. Both topography and bathymetry are measure relative to the global average of sea level.
1.3

Early Exploration of the Oceans

Ancient World Explorations: Many ancient cultures traveled the oceans for exploration, trade and conquest. Selected important highlights in history include:

* Ancient Egyptians used reed boats on the Nile River as early as 4,000 BC. Shipbuilding was known to the Ancient Egyptians as early as 3000 BC. Egyptian shipping trade extended throughout the eastern Mediterranean and the Red Sea, extending south around the Horn of Africa (modern Somalia).
* Minoan seafaring culture centered on the island of Crete and other islands in the western Mediterranean region (2600 to 1400 BC).
* Phoenician seafaring culture centered along coastal regions along with is now Lebanon, Syria, and Israel from about 1500 BC to 300 BC. Their shipping trade networks extended throughout the Mediterranean region into coastal waters of southern Europe and Northern Africa.
* Chinese exploration began as early as 3000-2500 BC, some by ship. China's maritime economic development began in the Zhou Period (1030-221 BC).
* Mayans traveled by boat throughout the Caribbean region (800 B.C-1521 AD).

Pacific Islanders
Pacific Islanders are descendants of ancient seafaring peoples that navigated and settled remote islands throughout the South Pacific region (Oceania) dating back 1000s of years.
• These people settled on many remote islands in what is now modern Micronesia, Polynesia, and Melanesia.
• Hawaii was inhabited around 500 AD explored from Marquesa Islands (and inhabited them around 300 AD).

The Middle Ages
Vikings explored the North Atlantic Ocean
• Norse seafaring peoples colonized Greenland and Iceland.

Early European navigators
• Explored the Mediterranean Sea, coastal Africa, and the Middle East.
• Developed a method to determine latitude using star navigation.

Age of Discovery (1492-1522)

Christopher Columbus made landfall in the Caribbean Sea in 1492 (He never set foot on North America.)
• Many journeys were undertaken to explore and exploit resources to the New World.
• Most exploration involved searching for new trade routes to Eastern Asian sources of precious spices & textiles.
Ferdinand Magellan's ship crew was first to circumnavigate the globe 1519. (Magellan didn't survived the journey, he was killed during a tribal skirmish on Mactan Island in the Philippines.)

Voyaging for science (1768-1780):
• Explorer Captain James Cook was a navigator and cartographer (map maker) for the British Royal Navy.
• Explored and traveled through all oceans on 3 different voyages
• Determined outline of the Pacific Ocean on 3rd voyage
• Modified shipboard diet to eliminate scurvy
• Used John Harrison’s chronometer (a timing device invented to determine longitude)

Eqyptian ship using a sounding pole to measure water depth.
Fig. 1-6. An Egyptian ship.
Leif_Ericsoon on a Viking Voyage
Fig. 1-7. Leif Ericsson on a Viking exploration voyage
Ben Franklin's map of the Gulf Stream
Fig. 1-8. Map of the Atlantic Gulf Stream compiled by Ben Franklin, published in 1769 is an example of early oceanographic research. Ponce de Leon first observed the Gulf Stream in 1513. Ben Franklin first charted the Gulf Stream with the help of a Nantucket sea captain.
View of a whale fishery from  Captain Cook's voyage
Fig. 1-9. View of a Whale Fishery from Captain Cook's voyage journal, 1790.
1.4

Essential Science Review Concepts for Oceanography

The following sections provide a brief overview of important concepts that are important to discussions in all subsequent chapters. These discussions are a mix of essential concepts provided in introductory courses in physical science, chemistry, biology, physics, and earth science.

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.

Science
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.
Scientific Method (steps in a cycle)
Fig. 1-10. The Scientific Method involves an ongoing cycle of inquiry.
NOAA research vessel
Fig. 1-11. NOAA research ship, the Ronald H. Brown, illustrates one of perhaps hundreds of vessels around the world involved in marine research and investigations.
The Alvin s
Fig. 1-12. The Alvin, a deep-sea exploration submersible.
Try out the Scientific Method! (A very valuable start to a college course!)

Example:
Use the scientific method to evaluate the data on this table comparing two variable factors: student attendance (number of classes missed in an introductory geology 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?
Data: Grades vs. Attendance
Fig. 1-13. Data: Attendance vs. Grade
1.5

Essential Chemistry and Physics Concepts for Oceanography

Aspect of chemistry and physics are discussed in nearly every chapter on oceanography. Below are highlights of important concepts.

What is Matter?

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 1-15.)

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. 1-14. Structure of an atom: this example is the element lithium composed of a nucleus of 3 protons, 4 neutrons, and an outer shell of 3 electrons spinning around the nucleus.
Periodic table highlighting elements most essential for life
Fig 1-15. The periodic table with essential elements highlighted.
Composition of the crust
Fig. 1-16. Composition of the 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. Silicon and oxygen are the two most abundant elements in the crust.
1.6

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).

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 1-19).

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. 1-17.
Salt crystals are held together by ionic bonds. Salt compounds dissolve in and precipitate from water.

Salt deposits in Death Valley
Fig. 1-18.
This view shows salt crystals precipitating on a dry lakebed in Death Valley, California.

Metals (native copper and gold), magnetite and pyrite
Fig. 1-19.
Metallic bonds occur in metallic minerals (like native copper and gold) and metalloid minerals (like magnetite and pyrite).
Quartz crystal
Fig. 1-20.
Most minerals are non-metallic crystalline compounds held together by covalent bonds (and will not transmit electricity). [Quartz]
   
1.7

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.

Radioactivity measured with a geiger counter
Fig. 1-21. 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.
1.8

Energy

Energy exists in several forms such as heat, kinetic energy (mechanical), light, potential energy, electrical, or other forms. 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.

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.

The electromagnetic spectrum
Fig 1-22. The electromagnetic spectrum is the range of wavelengths or frequencies over which electromagnetic radiation extends.
 
1.10

Gravity, Mass, and Density

Gravity is the weak force that attracts a body toward the center of the earth, or toward any other physical body having mass.

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. Gravity is the force that holds Earth in orbit around the Sun, and the Moon in orbit around the Earth. 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.
1.11

Zones of the Earth Climate System

On any location on the planet, the slow progress of seasonal changes are related to observable migration that the path the Sun follows through the sky over the cycle of one year. Seasons occur because:
a) the Earth spins (rotates) on its axis marked by the north and south poles; and,
b) the axis of the spinning Earth is tilted about 23.5° relative to ecliptic plane. (The ecliptic plain flat circular path the Earth follows as it revolves around the Sun in the orbital plane)(Figures 1-23 and 1-24).

Only twice a year, on the spring and fall equinoxes is the Sun directly above the equator (0°). The summer solstice occurs on June 21 when the Sun is directly overhead at noon along the latitude 23.5° north (a circle on the globe called the Tropic of Cancer). Likewise, the winter solstice occurs on December 20 when the is directly overhead at noon along the latitude 23.5° south (a circle on the globe called the Tropic of Capricorn).

The tropics are the region of the world between the parallels of latitude about north (Tropic of Cancer) and 23°5ʹ south (Tropic of Capricorn) on opposite sides of the equator (0°).

The term polar is used to describe the high latitude cold regions surrounding the Earth's north and south poles. The Arctic Circle runs 66.33° north of the equator. North of this line is the North Frigid Zone (also known as The Land of the Midnight Sun where the Sun never sets on the summer solstice). The Antarctic Circle is parallel of latitude approximately 66.33° south and defines the northern boundary of the South Frigid Zone. The Antarctic Circle marks the approximate limit south of which the Sun remains above the horizon all day on the summer solstice.

The regions between the tropics and the polar regions are called temperate zones (North Temperate Zone and South Temperate Zone).



Globe showing location of tropics, temperate zones, and polar zones
Fig. 1-23.
Location of tropics, temperate, and polar zones.
Seasons indicated by the tilt of the Earth's axis relative to it ecliptic orbit around the Sun.
Fig. 1-24
. Seasons are caused by the tilt in Earth's axis as it orbits around the sum.
1.12

Understanding Maps

Maps are perhaps the most important tools for navigation and evaluating features on the land's surface, underwater, or even underground. Maps are used for many issues involving land use and natural resource management. Maps have been used back into prehistoric times. However, the evolution of maps in the modern digital world has changed map making—enhancing their use in nearly all aspects of modern science, technology, and culture. Modern maps are created with geographic information systems (GIS). A GIS is a computer-based map-generating program that can merge geographic (spatial) information with many kinds of topical themes in database format. Such themes may consist of medical information (such as disease outbreak data), water resources, roads, buildings and civic infrastructure, power grid information, agricultural and biological information, etc.). Satellite data are increasingly used for nearly all aspects of mapping of the land, oceans, and weather patterns.
Map of Human Migration
Fig. 1-24.
Maps show thematic information in a geographic context. The theme of this map shows human migration routes on a world map base.
Many maps display relief or elevation information . Relief relates to height and shape characteristics of a landscape (such as high relief, low, relief, gentle relief, rugged relief, etc. Shaded-relief maps show changes in elevation (topography and bathymetry) using shades of gray or color.

What are Latitude and Longitude?

Locations on the Earth's surface are defined using latitude and longitude coordinate system (Figure 1-25).

Latitude is the angular distance of a place north or south of the earth's equator, usually expressed in degrees and minutes. Lines of latitude are called parallels. Latitude lines parallel the Equator. Each degree of latitude is approximately 69 miles (111 kilometers) apart. Latitude in the Northern Hemisphere can be determined by sighting on the North Star (which lies directly above the North Pole) and determining the angle of the star above the horizon (subtract it from 90°).

Longitude
is the angular distance of a place east or west of the Prime Meridian usually expressed in degrees and minutes. In order to make an accurate map of the stars for use in ship navigation, in 1884, a location indicating the precise location of 0° East-West was designated in the cross hairs of a telescope in the Royal Observatory (now located on the grounds of the National Maritime Museum) in Greenwich England. This line marks the reference location of the Prime Meridian now used in all global mapping (including GPS location systems). The International Date Line is on the opposite side of the earth located 180° east or west of the Prime Meridian.

A meridian is a circle of constant longitude passing through a given place on the earth's surface and the terrestrial poles. Longitude lines (of equal spacing measured in degrees) are widely spaced at the equator but converge at point at the North and South Poles. The Prime Meridian is designated 0° (zero degrees). Meridian lines east of the Prime Meridian are designated positive values (0° to 180° east); whereas meridian lines west of the Prime Meridian are designated negative values (-0° to -180°). At 180° east or west is the International Date Line. A degree of longitude is widest at the equator at 69.172 miles (111.321) and gradually shrinks to zero at the poles. At 40° north or south the distance between a degree of longitude is 53 miles (85 km).

Defining locations with a latitude-longitude coordinate system
—any location on the planet surface can be defined by a number in degrees, minutes, and seconds north or south of the Equator and east or west of the Prime Meridian. (Compare to hours, minutes, seconds on a clock!)

Example: Location of the Statue of Liberty in New York Harbor

The standard coordinates (in degrees, minutes, and seconds) of the Statue of Liberty are:
Latitude: 40°68′92"N
Longitude: 74°04′ 45"W.

Described in decimal degrees the coordinates of the Statue of Liberty are:
Latitude: 40.689758° N
Longitude:-74.045138° W.

An example from San Diego, California
The monument on top of Mount Soledad in La Jolla is located:
Latitude: 32.8398° N
Longitude: 117.2523° W.

Globe view of Earth from space
Fig. 38. A globe view is the only way to have perfect map projection!

Find the latitude and longitude of any named location or landscape feature on the GeoNames website.

The earth is round (a sphere like a globe) but maps are flat. As a result, maps that show large regions are distorted. Map projections are attempts to portray a portion of the Earth on a flat surface (examples are shown in Figures 1-26 to 1-28). The flattening of a map always causes some distortions of distance, direction, scale, and area. Large scale maps (such as a map of a continent or a world show much distortion, however, maps on small scales (such as a map of a town or neighborhood) have relatively little distortion. There are many map projection systems, each serves different purposes and has some variety of distortion. Learn more about map projections at the U.S. Geological Survey's Map Projections website.



A Global Positioning System (GPS) is a space-based global navigation satellite system that provides reliable location and time information in all weather and at all times and anywhere on or near the Earth when and where there is an unobstructed line of sight to four or more GPS satellites (Figure 1-29). GPS is now used for nearly all forms of digital map navigation.
Global projection
Fig. 1-25. Longitude
and Latitude projected on a globe
Mercator Map
Fig. 1-26.
Map of the world showing latitude and longitude in a Mercator (flat) projection
Map of world, Mercator Projection
Fig. 1-27.
Map of world showing with Mercator Projection - notice distortion in high latitudes because longitude lines are not converging
Map of North America Lambert Projection
Fig. 1-28.
Map of North America with Lambert Conic Projection - on this scale distortion of America is minimal, but look at South America.
Satellite network of the Global Positioning System
Fig. 1-29.
Satellite network of the Global Positioning System.
1.13

Geologic Time Scale

Geological time refers to 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. Geologists have subdivided periods in Earth's history is measured periods spanning millions or billions of years. The Geologic Time Scale has been established to name segments of time periods to help define the chronology of events (such as mountain range formation), the formation of rock units (such as the age of a lava flow), the age of fossils, organizing geologic map units, and other purposes. Figure 1-30 is a standard geologic time scale listing names of major time periods with time span information. 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.

College courses in historical geology examine what is currently known about the age of the Earth and the events as they are known or inferred to have occurred. For this course, the name of geologic time periods are used to explain the age of when rocks or sedimentary deposits formed, and where and how they occur in relation to other rocks and deposits associated with them. For example, rock layers containing dinosaur bones will correlate to the specific time period that the dinosaurs lived in the geologic past.

Every rock has a history! 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.

Note that the notions that the Earth being "old" (measured in billions of years) has not been all that popular with some religious groups throughout the ages. 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.

Fossils are traces or remains of prehistoric life now preserved in rock.
Paleontology: study of fossils
• Fossils are mostly found in sedimentary rocks
• Where found, fossils aid in interpretation of the geologic, geographic, and environmental past
• Fossils serve as important time indicators
• Fossils allow for correlation of rocks from different places
Geologic Time Scale
Fig. 1-30. Geologic Time Scale showing major geologic events in Earth history and the evolution of life on earth. New scientific discoveries are refining knowledge about the chronology and impacts or significance of events through deep Earth time.
Time Scale Clock
Fig. 1-31. If a second were 100,000 years - this classic diagram shows the distribution of 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!
1.14

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. 1-32. 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. 1-33.
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!

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 (bright stars having unique luminosity characteristics) in the "Andromeda nebula." Hubble 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 1-34). 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.

The milky way stands out in a clear night sky.
Fig. 1-34. 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 1-35). 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 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 [10 trillion km].) 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. 1-35. Andromeda Galaxy
1.15

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 1-36 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 1-37 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.

A field of possibly hundreds of galaxies in a distant region of the night sky.
Fig. 1-36. A field of galaxies.
A Spiral galxy (NGC 6814)
Fig. 1-37.
A spiral galaxy.
An elliptical galaxy, NGC 3610Fig. 1-38. An elliptical galaxy

An irregular galaxy combining two colliding galaxies NGC 4038 and NGC 4039
Fig. 1-39. An irregular galaxy

1.16

Earth's Place in the Observable Universe (Figure 1-40)

* 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 515000 miles/hr [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. 1-40. Earth's place in the Observable Universe.
1.17

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 1-41). 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.

Brief story of the Big Bang
Fig. 1-41.
A very brief story of the Big Bang and the evolution of the Observable Universe over an estimated 13.8 billion years.
1.18

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).

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 1-50 to 1-53). 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 dark space where nothing escapes.

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

Colorful stars in a massive cluster in the Omega Centari region. 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.

The Pleiades star cluster 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.

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

The Hertzspring_Russel Diagram of star classification Fig. 1-46. 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. 1-47. 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. 1-48. 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.
Subernava
Fig. 1-49. 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. 1-50. 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. 1-51.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. 1-52. 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. 1-53. The Hour Glass Nebula (discovered by the Hubble Telescope) is an unusual young planetary nebula located about 8,000 light years away.
1.19

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 1-54).

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. 1-54.
Our Solar System originated from gas, dust, and other matter that gravity pulled together in a stellar nebula about 5 billion years ago.
1.20

The Sun

The Sun is the star at the heart of our Solar System (Figure 1-55). 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 (1.4 million km) (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.

Sun
Fig. 1-55. 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 1-56).

* 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 layer of hot gas about 300 miles (480 km) thick 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 1-57).

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

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

1.21

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).

Sunspotes are dark spots on the Sun's surface.Fig. 1-58. Sunspots appear as dark splotches on the Sun's surface. Comparison of the relative size of sunspots to the size of the Earth.Fig. 1-59. Comparison of the relative size of sunspots to the size of the Earth. A solar flare erupting on the Sun;s surfaceFig. 1-60. A solar flare erupting on the Sun's surface. A large solar prominence erupting on the Sun's surfaceFig. 1-61. A large solar prominence erupting on the Sun's surface.
1.22
1.23

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. 1-64. 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 Planetary Systems

Jupiter Saturn Uranus Neptune

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

1.24

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).

Moon Fig. 1-72. 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
1.25

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 onemile (1.6 km) to about 480 miles (775 km) in diameter (Figure 1-73). 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 1-74). 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 1.5 million miles (2.4 million km) 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 1-75).
Asteroids
Fig. 1-73. Asteroids are solid objects in space consisting mostly of rock, dust, some metals, and possibly ice.
Comet Haley
Fig. 1-74. 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. 1-75.
An iron-nickel meteorite is magnetic.

Bollide over Oklahoma Panhandle, 9/30/2008
Fig. 1-76. 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 1-76 and 1-77). 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. 1-77. Map of reported bolide events 1994-2013.
1.26

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 1-78. (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.

Pluto
Fig. 1-78. Pluto
- formerly a planet, now it is called a planetesimal, or a dwarf planet in the Kuiper Belt. Pluto has 5 moons.
1.27

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 1-79). 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 1-80). Gravity gradually condenses material in nebulas into new star systems (see example in Figure 1-81).

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 1-82).
• 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 (beginning of fusion processes at it core), 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 (mostly dust).
• Larger outer planets began forming from fragments of ice and gas (hydrogen, H2O, CO2, CH4, 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 rock formed early in Earth's history are from the Jack Hills region of Australia. They ontain crystals of the mineral zircon radiometrically 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 1-83). 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.

Subernava
Fig. 1-79. Supernovas
are great explosions that partial to complete demolish aging stars, releasing new matter and gas to create a new generation of stars.
Nebula
Fig. 1-80. 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. 1-81. 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. 1-82. 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. 1-83. Proto Earth colliding with another object
1.28

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 1-84).

• 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. 1-84. 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.
1.29

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 1-85).
• 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. 1-85. Volcanic outgassing from the interior of the planet is still taking place, as illustrated by volcanic eruptions on Hawaii.
1.30

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 1-86).

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 1-87). 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 1-88).

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 1-89).

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
Europa
Gamymede
Enceladus
Fig. 1-86. Venus and Mars Fig. 1-87. Europa Fig. 1-88. Ganymede Fig. 1-89. Enceladus
1.31

Basic Geologic Principles

Some basic geologic concepts are helpful for explaining the origin of rocks that formed in ocean basins or are observable in rocky outcrops along coastlines. Rocks form in many ways, and because the Earth is so old, rocks that may have formed in one location may have been altered or moved long distances from it place of origin.
1.31

General Classification of Solid Earth Materials

Igneous rocks are rock formed from molten materials. These includes intrusive rocks (rocks cooled from molten material [magma] below the surface) and extrusive rocks formed on the Earth's surface by volcanism.

Sediments are solid fragments of inorganic or organic material that come from the weathering of rock and soil erosion, and are carried and deposited by wind, water, or ice.

Sedimentary rock
s are rocks that formed through the deposition and solidification of sediment, especially sediment transported by water (rivers, lakes, and oceans), ice ( glaciers), and wind. Sedimentary rocks are often deposited in layers, and frequently contain fossils.

Metamorphic rocks are rocks that were once one form of rock but has changed to another under the influence of heat, pressure, or fluids without passing through a liquid phase (melting).
1.32

Igneous Rocks

• The term igneous applies to rocks or minerals that have solidified from molten material.
• Molten material underground is call magma; when it erupts and flows on the surface it is called lava.
* When molten material cools, it crystallizes into rock.
• When magma intrudes other rocks underground and cools it forms intrusive igneous rocks (examples include granite, diorite, and gabbro). Slower cooling times underground result in bigger mineral crystals.
• Lava that extrudes on the surface as a volcanic eruption cools quickly, forming extrusive igneous rocks (examples include rhyolite, andesite, and basalt).

Igneous rocks are generally classified by their color and size of their crystals, and more specifically classified by their mineral composition. Study of igneous rocks has played an important role in deciphering the origin of rocks beneath and around ocean basins (discussed in Chapters 3 and 4).
Intrusive igneous rocks: granite, diorite, gabbro Extrusive igneous rocks: rhyolite, andesite, basalt Igneous provinces
Fig. 1-90. Intrusive (plutonic) igneous rocks Fig. 1-91. Extrusive (volcanic) igneous rocks. Fig. 1-92. Igneous regions of the world.
Basalt volcanic eruption Mount St. Helens is an andesite volcano Yosemite granites
Fig. 1-93. Basalt volcano: Pu'u'o'o volcano on Hawaii's Big Island. Fig. 1-94. Andesite volcano: Mount St. Helens in the Cascade Range, Washington.. Fig. 1-95. Granites exposed in core of Sierra Nevada Range.
1.33

Sediments and Sedimentary Rocks

Sediments are solid material that has settled from a state of suspension in a fluid (water, ice, or wind).
• When lithified (consolidated or cemented) becomes a sedimentary rock.
• Sediments are derived from weathering and erosion of pre-existing rocks.
• Sediments and sedimentary rocks can help tell the geologic history of an area (discussed in Chapter 5 about marine sediments).
• Sedimentary deposits are classified by grain size and source.
• Sedimentary deposits may contain fossils.

Sediments and sedimentary rocks cover much of the seafloor around the world. Most sedimentary rocks observed on land were deposited in ocean settings, along coastlines, or in shallow seaways that flooded onto the continents in the past. Sedimentary deposits and the fossils they contain have been important sources of information for resolving questions about Earth history and climate change.
Sedimentary Rocks
Fig. 1-96. Common sedimentary rocks include conglomerate, sandstone, shale, limestone, gypsum, and marl
1.34

Metamorphic Rocks

• Metamorphic rocks are formed by “changing” pre-existing igneous, sedimentary or other metamorphic rocks.
* Metamorphic processes involve changes caused by exposure to heat, pressure, and chemically-active fluids.
• Driving forces are increased heat and pressure as rocks are buried deep into the earth in association with mountain-building periods.
• They typically develop a fabric or texture that differentiates it from the original rock it formed from (called a protolith).
• Commonly found in ancient crustal rocks exposed in mountain ranges and in the core of continental landmasses.

Examples: quartzite, slate, marble, gneiss, schist, and serpentinite (the State Rock of California)
Metamorphic Rocks
Fig. 1-97. Common metamorphic rocks
1.35

The Rock Cycle

The rock cycle is a conceptual model of how earth materials form and change in the Earth’s crust over time. The rock cycle represents the series of events in which a rock of one type is converted to one or more other types and then back to the original type. Both products (rocks and sediments) and processes (such as melting, cooling, erosion, deposition, metamorphism, remelting) are part of this idealized cycle. The passage of geologic time is the essential component, although some processes are much faster than others. Note that all these types of processes are taking place simultaneously, but at different locations on and within the crust. It is important to note that rock cycle processes also occur on other rocky planets or moons, but rates may vary due to the presence (or lack of) atmospheric gases or fluids (including water) or availability of heat enough to melt rocks.
The Rock Cycle
Fig. 1-98. The Rock Cycle is a conceptual model that portrays processes and products changing over time
1.36

Uniformitarianism

The concept of the rock cycle is attributed to a Scottish physician, James Hutton (1726-1797), who studied rocks and landscapes and coastlines throughout the British Isles. Hutton's concepts were later promoted in a book entitled Principles of Geology by the Scottish geologist Charles Lyell (the book was released in 3 volumes in 1830-1833). Hutton and Lyell are considered the founders of modern geology. Hutton also promoted the theory of uniformitarianism. Uniformitarianism emphasizes 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 in Hutton's time promoted an alternative theory of catastrophism. Catastrophism is a theory 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, collapse of continental shelves (causing massive underwater landslides and tsunamis), 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.

Rock Formations

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).

James Hutton also contributed to a theories about 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 typical 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.

Rock formations preserved information about what conditions were like when the original sediments were deposited, such as on a river delta, a coastal beach environment, a ocean setting, or a massive dune field. Rock formations can also consist of igneous rocks, such as ancient lava flows or massive volcanic ash deposits. Rock formations typically represent materials that accumulated over period of hundreds of thousands, to many millions of years.
Stratum exposed along a shoreline (Anderson Reservoir, Morgan Hill, CA) Rock formations exposed along Calvert Cliffs, Chesapeake Bay, Maryland
Fig. 1-99. Strata exposed along a reservoir shoreline. Each layer represents sediments deposited under unique environmental conditions over a period of time (days, years, centuries). Fig. 1-100. Layers of sedimentary rock formations of the Cenozoic Era are exposed in many locations US coastlines. These are Calvert Cliffs on Chesapeake Bay, Maryland.
   
1.37

Methods For Determining the Age of Earth Materials and Features

Geochronology, the branch of earth sciences concerned with determining the age of earth materials and events through geologic time.

How do geoscientists determine the age of rocks or fossils? How do they figure out how long ago and in what order did geologic processes or events take place? For instance how do they know how often a volcano erupts or how often earthquakes take place. Geologists now have many ways to determine the age of materials using absolute and relative dating methods.

Absolute and Relative Dating Methods

Absolute dating is a general term applied to a range of techniques that provide estimates of the age of objects, materials, or sites in real calendar years either directly or through a process of calibration with material of known age. There are many methods of absolute dating rocks or other ancient materials. The methods of absolute dating used depends on whether suitable samples are available for testing.

Relative dating
is the science of determining the relative order of past events, without necessarily determining their absolute age (see below).

1.38

Decay of Radioactive Isotopes Used For Absolute Dating

Unstable isotopes emit particles and energy in a process known as radioactive decay. A parent isotope is an unstable radioactive isotope. A daughter product isotope results from the decay of a parent.

Radioactive decay occurs at known rates and using this you can determine the age of certain types of rocks.

Dating of materials that contain naturally-occurring radioactive isotopes is possible because the rates of decay are known. The radiation decay "clock" starts the moment a mineral in a rock forms (or for 14C when an organism dies).

A half-life is the time required for one-half (50%) of the parent to change to daughter product. The next half-life is when only a quarter of the original parent radionuclide remains, and so on. Age determinations can be determined by comparing the ratio of the parent and daughter isotome in a new (fresh) sample with the percentage in the old sample material being tested (Figure 1-101).

Commonly referenced studies of absolute dating utilize the radioactive decay of:
Parent Isotope
Daughter Isotope
Half Life
238U (unstable uranium isotope)
206PB (stable lead isotope)
~ 4.5 billion years
40K (unstable potassium isotope)
40Ar (stable argon isotope)
~ 1.25 billion years
14C (unstable carbon isotope)
14N (stable nitrogen isotope)
5,730 years
Note there are many other radionuclides used for absolute dating methods.

Sources of error in Absolute dating. Error can be caused by a variety of misinterpretation. Do we have a general good idea of the geologic history of the sample? (See Relative Dating below). Factors include:

The sample has been within a closed system, meaning no parent or daughter atoms have entered or the the sample. This is best assured by using fresh, unweathered rock samples.
• Decay rate is constant over geologic time.

Not all rocks can be dated by radiometric methods

Detrital sedimentary particles are not the same age as the rock in which they formed
Metamorphic rock age may not necessarily represent the time when the rock formed
Datable materials (such as volcanic ash beds and igneous intrusions) are often used to bracket ages
• Bracketing sedimentary ages using igneous rocks

Absolute dating
Fig. 1-101. Absolute dating methods.
Different isotopes are used to study different materials and geologic time ranges.
Hydrogen bomb blast in the 1950s
Fig. 1-102.
Nuclear bomb testing release large quantities of radionuclides into the global environment. Atmospheric and oceanic nuclear testing began with the first test on July 16, 1945 (Trinity Site in New Mexico). Most atmospheric testing ended in 1980, but (sadly) still continues underground.
1.39

Radiocarbon Dating

Radiocarbon dating is one of the most used method of absolute dating because of its useful dating window encompassing the past 100,000 years (it is especially useful for studying archeological features and young sedimentary deposits). 14C (isotope carbon -14) is a unstable radioactive isotope (radionuclide). Radiocarbon dating (using ratios of the isotopes of radioactive isotope14C to to stable isotopes 12C and 13C derived from buried or isolated organic or carbonate materials. The half life of 14C [unstable isotope carbon-14] is about 5,730 years. Radiocarbon dating has extensively used in archeological investigation and the study of climate change over the last several hundred thousand years, and precision methods now available make radiocarbon dating highly reliable. Radiocarbon dating is highly effective for extracting ages of organic materials (bone, tissues, wood, etc.) that have been isolated by burial and is effective for dating materials materials from ancient human activities going back for many thousands of years.
Radiocarbon Dating method
Fig. 1-103.
The science behind the radiocarbon absolute dating method.
1.40

Relative Dating

Relative dating is the science of determining the relative order of past events, without necessarily determining their absolute age (see above). Relative dating involved the study of fossils and the correlation or comparison of fossils of similar ages but from different regions where their age is known. Microfossils derived from sediments and cores from wells help in the subsurface exploration for oil and gas.

Relative dating
is useful and relatively easy compared with absolute dating
• Not all rocks can be dated with radioactivity (see above).
• This is the way we tell the ages of rock layers relative to each other.

Basic Geologic Principles Used For Relative Dating

These basic principles are easily observed in geologic outcrops, but have value for any number of scientific and technical applications beyond geology. Figure 1-104 and 1-105 illustrates the four laws that are used in resolving the age of rocks and the order in which they formed or geologic events occurred. The three laws are as follows:

Law of Original Horizontality—this law states that most sediments, when originally formed, were generally laid down horizontally. However, many layered rocks are no longer horizontal.

Law of Superposition—this law states that in any undisturbed sequence of rocks deposited in layers, and the oldest on bottom the youngest layer is on top. Each layer being younger than the one beneath it and older than the one above it.

Law of Cross-Cutting Relationships—this law states that a body of igneous rock (an intrusion), a fault, or other geologic feature must be younger than any rock across which it cuts through.

Inclusions
• An inclusion is a piece of rock within another rock.
• The rock containing the inclusion is younger

.
Basic geologic principles
Fig. 1-104. Basic geologic principles illustrated.
Basalt inclusion in granite
Fig.1-105. Example of a basalt inclusion in granite. The granite is younger than the basalt.
1.41

Unconformities: Gaps in the Geologic Record

Following on the Law of Original Horizontality and Law of Superposition, both Hutton and Lyell recognized erosional boundaries preserved between rock layers that represent gaps in the geologic record. They named these gaps unconformities. An unconformity is a surface between successive strata that represents a missing interval in the geologic record of time, and produced either by: a) an interruption in deposition, or b) by the erosion of depositionally continuous strata followed by renewed deposition. It should be noted that the unconformable gaps in the geologic record in one region may be represented by sedimentary deposits in another region. Through time, geologists and paleontologists have been able to correlate rock formations and associated unconformities across large regions and even across oceans to other continents. Research over the past two centuries have provided information that in many of the gaps, making a more complete history of the geologic record.

Several types of unconformable boundaries are recognized
:
  • nonconformity—an unconformity between sedimentary rocks and metamorphic or igneous rocks when the sedimentary rock lies above and was deposited on the pre-existing and eroded metamorphic or igneous rock
    .
  • angular unconformity—an unconformity where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers
    .
  • disconformity—an unconformity between parallel layers of sedimentary rocks which represents a period of erosion or non-deposition.

  • conformable boundary—an arrangement where layers of sedimentary strata are parallel, but there is little apparent erosion and the boundary between two rock layer surfaces resemble a simple bedding plane.
Types of unconformities
Fig. 1-106. Types of unconformities (boundaries between layered rocks)
 
Grand Canyon Grand Canyon block diagram The Waterpocket fold in Capitol Reef National Park Utah Sedimentary layers at the Del Mar Dog Beach
Fig. 1-107. Rock formations exposed in the Grand Canyon were originally deposited in different stages during the Precambrian and Paleozoic Eras. Some layers were deposited in shallow oceans, others layers accumulated on land. Fig. 1-108. A block diagram of the Grand Canyon shows the names of rock formations separated by unconformities (representing gaps in time when sediments were not deposited). Can you spot an angular unconformity? Fig. 1-109. Rock formations like these in Utah record information about 100 million years of Mesozoic Era of the region. These sedimentary rock layers were originally deposited horizontally, but were tilted by later mountain-building (tectonic) activity. Fig. 1-110. Layers of sedimentary rock formations with unconformities are exposed in many locations along the California coastline. For example, these sedimentary rock formations are exposed at the Dog Beach in Del Mar, CA.
Chapter 1 quiz questions
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