Introduction to Earth

Chapter Outline and Important Concepts

1. Geography and Science

1. 1. Geography is a generalized discipline that has the face of planet Earth as its focus.
      1. Rooted in the Greek words for “earth description,” geography is the areal differentiation of Earth’s surface.
   2. Studying the World Geographically
      1. Geography has two main branches, physical geography and human geography.
         1. Physical geography, also known as environmental geography, looks at those Earth elements that are natural in origin.
         2. Human geography looks at elements of human endeavor.
      2. Geography’s discipline foci are:
         1. It looks at how things differ from place to place.
         2. It has no particular body of facts or objects it can call wholly its own.
         3. It is a very broad field of inquiry and borrows its objects of study from related disciplines.
         4. It is both a physical science and a social science because it combines characteristics of each and can be conceptualized as bridging the gap between the two.
         5. The fundamental questions of geographic inquiry are:
            1. “Why is what where?”
            2. “So what?”
         6. It is interested in interrelationships; that is, examining how various factors (both physical and cultural) interrelate.
         7. The subject matter of this book is physical geography.
         8. The book focuses on the Earth’s physical elements, specifically:
            1. Their nature and characteristics, processes involved in their development, their distribution, and their interrelationships.
         9. This book also explores the ways humans have shaped the physical environment.
      3. Global Environmental Change
         1. This book focuses on both human-caused and natural processes that are currently altering the landscapes of the world.
         2. In this book, attention is paid to the accelerating impact of human activities on the global environment.
            1. The text’s focus boxes concentrate on this topic as well as sustainable energy.
         3. Globalization
            1. This book focuses on the process and consequences of an increasingly interconnected world.
               1. Connections between economics, cultures, and political systems
               2. These also have environmental components
            2. Geography’s global perspective and interest in both natural and human landscapes allow geographers to offer insights into the world’s most pressing problems.
         4. The Process of Science
            1. Science is described as a process that follows the scientific method:
               1. Observe phenomena that stimulates a question or problem
               2. Offer an educated guess (hypothesis) about the answer
               3. Design an experiment to test the hypothesis
               4. Predict the outcome of the experiment
               5. Conduct the experiment and observe the outcome
               6. Draw conclusions and formulate rules based on the experiment
            2. Science does not always exactly fit this methodology (i.e., data can be collected through observation), and therefore science is best thought of as a process for gaining knowledge.
               1. Although the term “scientific proof” is used, science does not actually prove things, but rather eliminates alternative explanations.
               2. Science is based on disproving these alternative explanations.
            3. In science, theories represent the highest order of understanding in a body of information.
               1. Theories are logical and well-tested explanations encompassing numerous facts and observations.
            4. The acceptance of theories is based on evidence and not beliefs, nor the pronouncements of “authorities.”
               1. Theories are revised based on new observations and new evidence.
               2. The scientific method is a self-correcting process based on the refining of scientific knowledge through peer review, which ensures that research and conclusions meet rigorous standards of scholarship.
               3. New scientific evidence may make scientists change their minds, as well as lead to disagreement within the scientific community, but good science tends to take a cautious stance toward conclusions that are drawn.
                  • As such, scientists preface findings by stating that “the evidence suggests” or “the results most likely show.”
                  • This apparent circumspection can lead to a misconception surrounding the validity of the scientific method on the part of the general public.
                  • However, this very circumspection spurs scientists to further seek knowledge and understanding.
               4. This text presents the fundamentals of physical geography as supported by scientific research and evidence.
               5. Citizens as scientists
                  1. Volunteers can collect and compile scientific data.
                  2. Consistency is a concern in data collection methods and instruments used to collect data.
               6. Numbers and Measurement Systems
                  1. This text offers measurements in both the International System of measurement, from the French Système International (abbreviated SI, sometimes called the “metric system”), and the traditional (or English) system. SI is an extension of the metric system, devised in the 1790s to provide simple and scientific standard units.
                  2. SI-to-English conversions can be found in Tables 1-2 and 1-3, and in Appendix I.

 2. Environmental Spheres and Earth Systems

1. 1. Earth’s Environmental Spheres
      1. Earth’s surface is a complex interface where four spheres meet and, to some degree, overlap and interact. These four spheres provide important organizing concepts for the systematic study of Earth’s physical geography:
      2. Lithosphere
      3. Atmosphere
      4. Hydrosphere
         • A subcomponent of the hydrosphere that encompasses frozen water and snow is the cryosphere.

1. d) Biosphere

1. Earth Systems
   1. System: a collection of things and processes connected together and operating as a whole.
2. Closed Systems
   1. Isolated from influences outside that system.
   2. Earth is a closed system in regard to matter, but not to energy.
3. Open Systems
   1. Matter and energy are freely exchanged.
   2. Most Earth systems are open.
4. Equilibrium
   1. When inputs and outputs are in balance over time
5. Interconnected Systems
   1. Many Earth systems are connected together.
      1. For example, a glacier is connected to the hydrologic cycle, wind and pressure patterns, solar energy, and so on.
   2. Feedback Loops
      1. Some systems produce outputs that reinforce change.
         1. For example, the reduction in Arctic ice reduces reflectivity, which in turn allows more solar energy to be absorbed, which then causes more Arctic ice to melt, which further reduces reflectivity, and so on.

3. Earth and the Solar System

1. 1. The Solar System
      1. A geographer’s concern with spatial relationships properly begins with the relative location of Earth in the universe.
         1. Solar system—system of eight planets (and dwarf planets, moons, comets, asteroids, meteors) revolving around the Sun; Earth is third.
         2. Sun—medium-sized star that makes up more than 99.8 percent of the solar system’s mass.
         3. The Sun is one of perhaps 200 billion stars in the Milky Way Galaxy, which is one of hundreds of billions of galaxies in the universe.
      2. Origins
         1. It is generally accepted that the universe began with the big bang some 13.7 billion years ago.
         2. Our solar system originated between 4.5 and 5 billion years ago.
         3. Earth’s planetary orbit lies in nearly the same plane as all the other planets. (Pluto, which has lost its planetary status, is somewhat askew.)
            1. Earth, like all the planets, revolves around the Sun from west to east.
         4. Earth rotates from west to east on its own axis.
      3. The Planets
         1. The terrestrial planets (the four inner planets—Mercury, Venus, Earth, and Mars) are smaller, denser, and less oblate and rotate on their axes more slowly than the Jovian planets.
            1. Terrestrial planets are composed mainly of mineral matter.
         2. The Jovian planets (the four outer planets—Jupiter, Saturn, Uranus, and Neptune) are larger, more massive, less dense, and more oblate than the terrestrial planets.
            1. Jovian planets are composed mostly of gas.
         3. In more recent years, more small-sized “Pluto-like” dwarf planets and comets have been discovered in our solar system beyond Neptune in the Kuiper Belt.
            1. In June 2008 the International Astronomical Union reclassified Pluto and other similar objects in our solar system as “plutoids.”
         4. The Size and Shape of Earth
            1. Frame of reference determines whether one looks at Earth as being large or small.
            2. Earth possesses a diameter of only 13,000 kilometers, which is negligible in comparison to the scale of the universe.
            3. In comparison to this diameter, Earth’s relative relief is also quite small.
         5. The Size of Earth
            1. Its surface varies by 19,883 meters (65,233 feet) in elevation from the highest mountain peak, Mt. Everest, at 8850 meters (29,035 feet) to the deepest ocean trench, Mariana Trench, −11,033 meters (−36,198 feet)
         6. The Shape of Earth
            1. Earth is an oblate spheroid rather than a true sphere, though the variation from true sphericity is exceedingly minute, and so for most purposes it can properly be considered a sphere.
               1. Greek scholars as early as the sixth century c. began believing Earth was a sphere, with several making independent calculations of its circumference that were all close to reality.
                  • Eratosthenes did so by observing the angle of the Sun’s rays in Alexandria and Syene on the same day.
               2. Earth’s shape is affected by two main facts:
                  1. It bulges at the midriff because of the pliability of Earth’s lithosphere.
                     • Therefore, its shape is an oblate spheroid.
                  2. It has topographical irregularities.
                     • In context of Earth’s full dimensions, these variations are minute.
                     •  
                  3. The Geographic Grid—Latitude and Longitude
                     1. A system of accurate location is necessary to pinpoint with mathematical precision the position of any spot on Earth’s surface.
                        1. The grid system is the simplest technique, using a network of intersecting lines.
                        2. Graticule—the grid system for mapping Earth that uses a network of parallels and meridians (lines of latitude and longitude).
                           1. Four Earth features provide the set of reference points essential to establish the graticule as an accurate locational system.
                              • North Pole, South Pole, rotation axis, and equatorial plane (an imaginary plane passing through Earth halfway between the poles and perpendicular to the rotation axis).
                           2. Equator—the imaginary midline of Earth, where the plane of the equator intersects Earth’s surface. It is the parallel of 0° latitude.
                        3. Great Circles
                           1. A great circle is the largest circle that can be drawn on a sphere; it must pass through the center of the sphere; it represents the circumference and divides the surface into two equal halves or hemispheres.
                              1. Circle of Illumination—a great circle that divides Earth between a light half and a dark half.
                           2. Small circle—a plane that cuts through a sphere without passing through the center.
                           3. Graticule—the grid system of the Earth consisting of lines of latitude and longitude.
                        4. Latitude
                           1. Latitude—the distance measured north and south of the equator; it is an angular measurement, so is expressed in degrees, minutes, and seconds.
                           2. Parallel—an imaginary line that connects all points of the same latitude; because they are imaginary, they are unlimited in number.
                           3. Seven parallels are particularly significant:
                              1. Equator, 0°
                              2. Tropic of Cancer, 23.5° N
                              3. Tropic of Capricorn, 23.5° S
                              4. Arctic Circle, 66.5° N
                              5. Antarctic Circle, 66.5° S
                              6. North Pole, 90° N
                              7. South Pole, 90° S
                           4. Descriptive Zones of Latitude
                              1. Regions on Earth are sometimes described as falling within general bands of latitude.
                                 1. Low latitude—generally between the equator and 30° N and S
                                 2. Midlatitude—between about 30° N and S
                                 3. High latitude—latitudes greater than about 60° N and S
                                 4. Equatorial—within a few degrees of the equator
                                 5. Tropical—within the tropics (between 23.5° N and 23.5° S)
                                 6. Subtropical—slightly poleward of the tropics, generally around 25–30° N and S
                                 7. Polar—within a few degrees of the North or South Pole
                              2. Nautical Miles
                                 1. The actual length of 1° of latitude varies according to where it is being measured on Earth because of the polar flattening of Earth. Even with the variation, each degree has a north–south length of about 111 kilometers (69 miles).
                                 2. A nautical mile is defined by the distance covered by 1′ of latitude (1.15 statute miles, or 1.85 kilometers).
                              3. Longitude
                                 1. Longitude—the distance measured east and west on Earth’s surface.
                                 2. Meridian—imaginary line of longitude extending from pole to pole (aligned in a north–south direction), crossing all parallels at right angles. (It’s not to be confused with its other definition, the Sun’s highest point of the day.)
                                    1. Meridians are not parallel to each other, except where they cross at the equator, where they are also the farthest apart.
                                       • They close together northward and southward, converging at the poles.
                                    2. Establishing the Prime Meridian
                                       1. Established at an international conference in Washington, DC, in 1883
                                       2. The meridian passing through the Royal Observatory at Greenwich, England, was selected because it was already used as a standard meridian by two-thirds of the world’s shipping lines.
                                    3. Measuring Longitude
                                       1. Longitude is measured from this meridian both east and west to a maximum of 180°.
                                       2. The distance between any two meridians varies because they converge at the poles.
                                          1. This variation is, however, predictable.
                                       3. Locating Points on the Geographic Grid
                                          1. The network of intersecting parallels and meridians creates a global reference grid that allows locations to be denoted and located with great precision.

4. Earth–Sun Relations and the Seasons

1. 1. Earth Movements
      1. The functional relationship between Earth and the Sun is vital because life on Earth is dependent on solar energy.
         1. Two basic Earth movements are critical for continuously changing the geometric perspective between the two:
            • Earth’s daily rotation on its axis
            • Earth’s annual revolution around the Sun
         2. Earth’s Rotation on Its Axis
            1. Earth rotates toward the east on its axis, with one complete rotation taking 24 hours.
               1. This eastward spin creates an illusion that the celestial bodies are rising in the east and setting in the west.
            2. Although the speed of rotation varies from place to place, it is constant in any given place, so humans do not experience a sense of motion.
            3. This rotation has several striking effects on the physical characteristics of Earth’s surface:
               1. There is an apparent deflection in the flow path of both air and water called the Coriolis effect, which deflects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
               2. Any point of the surface passes through the increasing and decreasing gravitational pull of the Moon and the Sun.
               3. Most important of all, there is a diurnal (daily) alternation of light and darkness, which in turn influences local temperatures, humidity, and wind movements.
            4. Earth’s Revolution Around the Sun
               1. Tropical year—the time it takes Earth to complete one revolution around the Sun; for practical purposes it can be simplified to 365.25 days.
               2. Earth’s revolution is an ellipse, which varies the Earth–Sun distance.
                  1. The varying distance between Earth and the Sun is not an important determinant of seasonal temperature fluctuations.
                     • Perihelion—the point in an orbit that takes a planet nearest to the Sun (for Earth, it is 147,166,480 kilometers, or 91,455,000 miles, on January 3).
                     • Aphelion—the point in an orbit that takes a planet farthest from the Sun (for Earth, it is 152,171,500 kilometers, or 94,555,000 miles, on July 4).
                  2. Inclination of Earth’s Axis
                     1. Plane of the ecliptic—the imaginary plane that passes through the Sun and through every point of Earth’s orbit around the Sun.
                        1. It is not perpendicular to Earth’s rotation axis, which allows for seasons to occur.
                     2. Inclination of Earth’s axis—the degree to which Earth’s rotation axis is tilted (about 23.5° away from the perpendicular).
                  3. Polarity of Earth’s Axis
                     1. Polarity of the rotation axis—also called parallelism; occurs because Earth’s axis points toward Polaris, the North Star, no matter where Earth is in its orbit.
                     2. The combination of rotation, revolution, inclination, and polarity result in the seasonal patterns experienced on Earth.

5. The Annual March of the Seasons

1. During the year the changing relationship of Earth to the Sun results in variations in day length and in the angle at which the Sun’s rays strike the surface of Earth. As a result of this, three conditions are noted in this section:
   1. The latitude (or subsolar point or the declination of the Sun) receiving the vertical rays of the Sun
   2. The solar altitude at different latitudes
   3. The length of day at different latitudes
2. June Solstice
   1. June solstice—on or about June 21, the North Pole is oriented most directly toward the Sun.
      • On this day the direct rays of the Sun at noon strike perpendicular to the surface of the Tropic of Cancer (23.5° N).
      • The day lengths are longer in the Northern Hemisphere and shorter in the Southern Hemisphere on this day.
      • Day length is equal on the equator because the circle of illumination (the line dividing halfway between daylight and nighttime on Earth) bisects the equator evenly.
      • Arctic Circle—the parallel of 66.5° N latitude; experiences 24 hours of light on this day.
      • Antarctic Circle—the parallel of 66.5° S latitude; experiences 24 hours of darkness on this day.
   2. September Equinox (also known as the autumnal equinox)
      1. Occurs on or about September 22 and all latitudes experience 12 hours of day and 12 hours of night. This is because all latitudes are bisected evenly by the circle of illumination.
      2. The equinoxes represent the midpoints in the shifting of direct rays of the Sun between the Tropic of Cancer and the Tropic of Capricorn.
   3. December Solstice
      1. December solstice—on or about December 21, the South Pole is oriented most directly toward the Sun.
         • On this day the direct rays of the Sun at noon strike perpendicular to the surface of the Tropic of Capricorn (23.5° S).
         • The day lengths are longer in the Southern Hemisphere and shorter in the Northern Hemisphere on this day.
         • Day length is equal on the equator because the circle of illumination (the line dividing halfway between daylight and nighttime on Earth) bisects the equator evenly.
         • Arctic Circle—the parallel of 66.5° N latitude; experiences 24 hours of darkness on this day.
         • Antarctic Circle—the parallel of 66.5° S latitude; experiences 24 hours of light on this day.
      2. March Equinox (also known as vernal equinox)
         1. Occurs on or about March 20 and all latitudes experience 12 hours of day and 12 hours of night. This is because all latitudes are bisected evenly by the circle of illumination.
      3. Seasonal Transitions
         1. It is important to understand the transitions in day length and Sun angle that take place on other days of the year that are not solstices or equinoxes.
      4. Latitude Receiving the Vertical Rays of the Sun
         1. The vertical rays of the Sun can only strike between the Tropic of Cancer and the Tropic of Capricorn.
         2. Between the March equinox and the June solstice, the vertical rays of the Sun migrate northward until they reach the Tropic of Cancer.
         3. Latitudes north of the Tropic of Cancer never experience the vertical rays of the Sun, so the June solstice marks the day when they are at their highest angle.
         4. After the June solstice the vertical rays migrate south, and the situation is similar in the Southern Hemisphere between the September equinox and the December solstice, with the Sun’s vertical rays reaching their farthest point south at the Tropic of Capricorn on December 21.
      5. Day Length
         1. Only at the equator is day length constant throughout the year.
         2. This shifting of the vertical rays of the Sun has a direct influence on day length.
         3. Day length for a given hemisphere is longer as the vertical rays of the Sun approach the tropics within that hemisphere.
         4. Day length continues to lengthen and reaches 12 hours during that hemisphere’s equinox (when the vertical rays of the Sun are on the equator).
         5. Day length then continues to increase and reaches its maximum during that hemisphere’s solstice (when the direct rays of the Sun are at the tropic in that hemisphere).
         6. Day length then diminishes as the direct rays of the Sun migrate back toward the equator and subsequently the tropic in the opposite hemisphere.
      6. Day Length in the Arctic and the Antarctic
         1. On the March equinox the Sun rises at the North Pole and is continuously above the horizon until the following equinox in September.
         2. Constant daylight extends southward to the Arctic Circle until the Sun’s vertical rays reach their highest point on June 21.
         3. Daylight begins to decrease northward toward the North Pole until the September equinox.
         4. Between the September equinox and the March equinox, the North Pole is in continual darkness.
         5. This overall pattern is reversed for the Southern Hemisphere, with increasing daylight between the South Pole and the Antarctic Circle between the September and the March equinoxes.
      7. Significance of Seasonal Patterns
         1. Both day length and the angle at which the Sun’s rays strike Earth are principal determinants of the amount of insolation received at any particular latitude.
         2. Tropical latitudes are always warm/hot because they always have high sun angles and consistent days close to 12 hours long.
         3. Polar regions are consistently cold because they always have low sun angles.

6. Telling Time

1. 1. It was difficult to compare time at different localities when transportation was limited to foot, horse, or sailing vessel. Thus there were no standard times; each community set its own time by correcting its clocks to high noon (meridian, not to be confused with meridian of longitude).
   2. Standard Time
      1. Use of local solar time created increasing problems with the advent of the telegraph and the railroad; railroads stimulated the development of a standardized time system.
      2. An 1884 international conference divided the world into 24 standard time zones, each extending over 15° of longitude (it also determined the prime meridian).
         1. Universal Time Coordinated (UTC)—formerly Greenwich Mean Time (GMT); a standardized time system that uses the local solar time of the Greenwich (prime) meridian as its standard.
            • In international waters, time zone boundaries are defined specifically and consistently.
            • Over land areas, however, zone boundaries vary, sometimes undergoing great manipulation for political and economic convenience.
         2. International Date Line
            1. International Date Line—Along with the prime meridian, provides the anchor for the framework of time zones. It is the line marking where new days begin and old days end on the surface of the Earth.
               1. Experiences a time difference of an entire day from one side of the line to the other.
               2. Generally, the line falls on the 180th meridian except where it meanders to ensure two island groupings aren’t split apart in their schedules (Aleutian Islands and South Pacific islands).
               3. The extensive eastern displacement of the date line in the central Pacific is due to the widely scattered distribution of many of the islands of the country of Kiribati.
            2. Daylight-Saving Time
               1. Daylight Saving Time—a practice by which clocks are set forward by an hour (or more) to extend daylight into the usual evening hours.
                  1. Created originally in Germany to help conserve electricity for lighting. Became U.S. national policy, though Arizona, Hawaii, and part of Indiana exempt themselves under the Uniform Time Act. Now gaining international acceptance.