1. Title Page Photo
“Come forth into the light of things, Let
Nature be your teacher.”
—William Wordsworth
Vocabulary
• asthenosphere (p. 388) • mineral (p. 389)
• basalt (p. 392) • Mohoroviˇci´c discontinuity (Moho)
• contact metamorphism (p. 398) • (p. 387)
• crust (p. 387) • outcrop (p. 391)
• external (geomorphic) processes • outer core (p. 388)
• (p. 404) • plutonic (intrusive) igneous rock
• geomorphology (p. 402) • (p. 392)
• granite (p. 392) • pyroclastics (p. 391)
• igneous rock (p. 391) • relief (p. 403)
• inner core (p. 388) • rock (p. 391)
• internal (geomorphic) processes • rock cycle (p. 400)
• (p. 404) • sedimentary rock (p. 394)
• landform (p. 402) • silicate (silicate minerals) (p. 389)
• lava (p. 391) • strata (p. 396)
• lithosphere (p. 388) • topography (p. 401)
• magma (p. 391) • uniformitarianism (p. 404)
• mantle (p. 388) • volcanic (extrusive) igneous rock
• metamorphic rock (p. 398) • (p. 392)
The Structure of Earth
• Humans have not penetrated more than one-
thousandth of Earth radius.
• Have inferential knowledge of interior, through
monitoring shock waves transmitted through
Earth from earthquakes or from human-made
explosions.
– Knowledge is incomplete.
– Deduced that it has a heavy inner core surrounded by
three concentric layers of various composition and
density.
• Four regions are the crust, mantle, outer core, and inner
core
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2. The Structure of Earth
• Introduction
– Core
• Inner core
• Outer core
– Mantle
– Crust
– Fig. 13-1
The Crust
• Crust—outermost solid layer
of Earth, consisting of broad
mixture of rock types.
– On average, crust three times as
thick under continents as under
ocean.
– Makes up less than 1 percent of
Earth’s volume.
– Mohorovičić discontinuity
(Moho)—the boundary between
Earth’s crust and mantle.
• Thought to be a narrow zone with
significant change in mineral
composition.
The Mantle
• The Mantle is that portion of Earth
beneath the crust and surrounding
the outer core, about to depth of
2,900 kilometers (1,800 miles).
– Largest volume of all four shells.
– Scientists believe three zones within
mantle: lithosphere, asthenosphere,
mesosphere.
• Lithosphere—the uppermost zone of
mantle and the crust together. (Also,
tectonic plates consisting of the crust and
upper rigid mantle. Sometimes used as a
general term for the entire solid Earth.)
• Asthenosphere—plastic layer of the
upper mantle that underlies the
lithosphere. Its rock is very hot and
therefore weak and easily deformed.
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3. The Inner and Outer Core
• Outer core—the (molten) liquid
shell beneath the mantle that
encloses Earth’s inner core.
– Responsible for generating Earth’s
magnetic field.
– The north magnetic pole migrates.
– The magnetic field also weakens
and undergoes magnetic reversals
at regular intervals.
• Inner core—the supposedly solid,
dense, innermost portion of Earth,
believed to consist largely of
iron/nickel or iron/silicate.
– Understanding of crust and upper
mantle has fundamentally changed
in last three decades.
Plate Tectonics and the Structure
of Earth
• Continental drift—theory
that proposes that the
present continents were
originally connected as one
or two large landmasses that
have broken up and literally
drifted apart over the last
several million years.
• Plate tectonics—a coherent
theory of massive crustal
rearrangement based on the
movement of continent-sized
lithospheric plates.
Composition of Earth
• Mineral—a naturally
formed inorganic solid
substance that has an
unvarying chemical
composition and
characteristic crystal
structure.
• About 4,400 identified,
with new types being
Fig. 13-3. Quartz crystal, pure silica (SiO2)
found each year.
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4. Minerals
• In order for a substance
to be considered a
mineral it must be
1. Solid
2. Naturally found in nature
3. Inorganic
4. Possess a specific
chemical composition
5. Contain atoms arranged in
a regular pattern to form Fig. 13-4. Iron pyrite
solid crystals. crystals(FeS2)
Minerals
• Seven principal categories of rock-forming minerals (on
basis of chemical properties and internal structure).
1. Silicates—a category of minerals composed of silicon and
oxygen combined with another element or elements.
• Largest and most important group; most are hard and durable.
2. Oxides—a category of minerals composed of oxygen combined
with another element.
• Quartz has chemical composition of oxide, but classified as silicate
because of its internal structure.
3. Sulfides—a category of minerals composed of sulfur, combined
with another element or elements.
• Includes many of the most important ore minerals.
Minerals
4. Sulfates—a category of minerals composed of
sulfur and oxygen, combined with another
element or elements.
– Calcium is the principal combining element.
5. Carbonates—mineral that is a carbonate
compound of calcium or magnesium.
6. Halides—a category of minerals that is notably
salty.
– Least widespread.
7. Native elements—those minerals that aren’t
combined chemically with others, but appearing
as discrete elements (e.g., gold and silver).
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5. Rocks
• Rock—solid material
composed of
aggregated mineral
particles (in
lithosphere).
• Outcrop—surface
exposure of bedrock.
• Bedrock—buried
layer of residual rock
that has not
experienced erosion.
– Three types of rocks
• Igneous
• Sedimentary
• Metamorphic
- Fig. 13-6
Igneous Rocks
• Igneous rock—rock
formed by solidification of
molten magma.
– Many kinds, but principal
shared trait is crystalline
structure.
• Magma—molten material
in Earth’s interior.
• Pyroclastics – rocks
formed from the “welding”
together of tiny pieces of
volcanic rock.
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6. Igneous Rocks
• Classification of igneous rocks based on
mineral composition and texture.
– Quantity of silica is one of the most important
variables.
• Felsic—contain large portions of light-colored
silicate minerals.
– Quartz and feldspar
• Mafic—contain low amounts of silicate.
– Contain a large portion of dark-colored silicate minerals
such as olivine and pyroxene.
Igneous Rocks
• Plutonic (Intrusive) Rocks—rocks that cool and solidify
beneath Earth’s surface (may be pushed up to surface or
exposed through erosion).
– Granite is most common and well known.
– Large mineral crystals because of slow rate of cooling.
• Volcanic (Extrusive) Rocks—molten rock ejected onto
Earth’s surface, solidifying quickly in the open air.
– Basalt is most common.
– Also obsidian, tuff, and pumice.
• Small mineral crystals because of rapid rate of cooling.
– Fig. 13-8a. Sylvan Lake, Black Hills, SD
Granite
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7. – Volcanic (Extrusive) Rocks
• Small mineral structure (fine-grained)
• Dark-colored, generally (mafic igneous rock)
• Basalt most common (extensive seafloor bedrock)
– Fig. 13-17
– Fig. 13-19. Snake River Canyon, Idaho.
Basalt
Sedimentary Rocks
• Sediment—small particles of rock
debris or organic material
deposited by water, wind, or ice.
• Sedimentary rock—rock formed
of sediment that is consolidated by
the combination of pressure and
cementation.
– During sedimentation, materials
sorted roughly by size (the finer
particles carried farther than heavier
particles).
• Strata (plural; stratum, singular)—
distinct layers of sediment.
– Results in parallel structure
(stratification), with layers varying in
thickness and composition.
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8. Sedimentary Rocks
• Clastic Sedimentary Rocks
– Composed of fragments of preexisting rocks.
• AKA clastic or detrital
• For example, shale and sandstone.
• When sedimentary rock is composed of rounded
particles, it is called conglomerate.
Sedimentary Rocks
• Chemical and Organic Sedimentary Rock
– Chemically accumulated: precipitation of
soluble materials or chemical reactions.
• For example, calcium carbonate and limestone.
– Organically accumulated: remains of dead
plants or animals.
• For example, coal and limestone.
– Nearly horizontal layers of limestone and shale
Limestone
– Fig. 13-11
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10. – Chemical and Organic Sedimentary Rocks
• Chemical Precipitation (Limestone most common result)
• Compaction of organic sediments (e.g., limestone and coal
formations)
– Fig. 13-11. (a) Layers of limestone and shale. (b) Limestone with fossil mollusks.
– Relative Abundance of Sedimentary Rock Types
– Fig. 13-14
Metamorphic Rocks
• Metamorphic rock—rock that was originally something
else (igneous or sedimentary) but has been drastically
changed by massive forces of heat and/or pressure
working on it from within Earth.
– Contact metamorphism
• When magma comes in contact with surrounding rocks.
– Regional metamorphism
• Large volumes of rock are subject to heat and pressure.
• Process recrystallizes and rearranges mineral components.
• Foliation—Prominent alignment of minerals.
• Some predictability, such as limestone metamorphized becomes
marble.
• Sometimes metamorphosis so great, can’t determine nature of
original rock.
• Most common are schist and gneiss.
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12. – Common Metamorphic
Rocks and Their
Counterparts
• Marble limestone
• Quartzite sandstone
• Slate Shale
Metamorphic rocks with
multiple counterparts:
• Gneiss
• Schist
– Slate, Northampton County, PA
(Source: Richard A. Crooker)
The Rock Cycle
• There is an
ongoing
recycling of
lithographic
material via
the rock
cycle
(Figure 13-
18 on page
400).
Continental and Ocean Floor
Rocks
• Lithosphere has very uneven
distribution of sedimentary,
igneous, and metamorphic
rocks.
– Sedimentary rocks dominant
on surface of Earth, both in
United States and rest of
world.
– This dominance, however, is
only on surface, as
sedimentary cover is not thick.
• Averages less than 2.4
kilometers (1.5 miles).
• Assume that igneous make
up the bulk of the crust, but
metamorphic rocks might
because of enormous
pressures at play beneath
crustal surface.
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13. Continental and Ocean Floor
Rocks
• Continental crust is primarily made up of
silica and aluminum.
– Sial for short.
– 2.7 grams per cubic centimeter
Continental and Ocean Floor
Rocks
• Oceanic crust is primarily made up of silica
and magnesium.
– Sima for short.
– 3.0 grams per cubic centimeter.
Continental and Ocean Floor
Rocks
• Isostasy—maintenance of the hydrostatic
equilibrium of Earth’s crust.
– Basically, where material is added, crust will sink, but
it will rise when material is removed.
– Variety of causes result in isostatic reactions.
• For example, deposition of sediment or accumulation of
glacial ice vs. erosion as ice sheet melts or large body of
water drains.
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14. The Study of Landforms
• Focus on topography—the surface
configuration of Earth.
• Landform—an individual topographic feature.
• Geomorphology—the study of the
characteristics, origin, and development of
landforms.
• Focusing just on land surfaces, study must
encompass 150 million square kilometers (58
million square miles) scattered over seven
continents and innumerable islands.
The Study of Landforms
• Such study is complex endeavor and requires
organized approach, including examining following four
elements.
1. Structure—nature, arrangement, and orientation of the
materials in feature being studied.
• Geologic underpinning of landform.
2. Process—the actions that have combined to produce the
landform.
• Encompasses interaction of forces such as geologic, hydrologic,
atmospheric and biotic.
3. Slope—fundamental aspect of shape for any landform.
4. Drainage—refers to movement of water (from rainfall and
snowmelt).
The Study of Landforms
• After identifying the previous four basic
elements, geographer can analyze topography.
• Fundamental questions of geographic inquiry:
1. What? (the form of features)
2. Where? (the distribution and pattern of landform
assemblage)
3. Why? (an explanation of origin and development)
4. So what? (the significance of the topography in
relationship to other elements of environment and to
human life and activities)
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15. The Study of Landforms
• Some Critical Concepts
– Basic Terms
• Relief—the difference in elevation between the
highest and lowest points in an area (e.g., the
vertical variation from mountaintop to valley
bottom).
Internal and External Geomorphic
Processes
• Variety of topography reflects complexity of
interactions between process and structure.
– Internal Processes
• Internal processes operate within Earth, drawing energy from
heat.
• In general, they are building forces, increasing relief of land
surface.
– External Processes
• External processes operate at base of atmosphere
(subaerial), drawing energy from sources above lithosphere
(atmosphere or oceans).
• Better understood than internal processes; behavior is
predictable.
• In general, they are wearing-down or destructive forces,
diminishing relief of land surface.
Internal and External Geomorphic
Processes
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16. Uniformitarianism
• Uniformitarianism—the concept that “the
present is the key to the past” in
geomorphic processes.
• The processes now in operation have also
operated in the same way in the past and
should also operate in future.
Geologic Time
• Geologic time
enumerates temporal
expanses of almost
unfathomable scope.
– Geologic time
encompasses millions and
hundreds of millions of
years.
• Four eras, three most
recent being subdivided
into 12 periods.
• Two most recent periods
divided into 7 epochs.
Geologic Time
• Chapter 13 offers chart of geologic time expressed in equivalent 1-year
scale.
– On one-year scale, first 4 months, planet was lifeless.
– One-celled life appeared in early May.
– Multicelled organisms began evolving in early November.
– Antediluvian fishes, the first vertebrates, appeared about November 21.
– Amphibians appeared late November.
– Vascular plants appeared about November 27.
– Reptiles began era of dominance about December 7.
– Mammals arrived about December 14; birds arrived December 15.
– Flowering plants arrived December 21.
– December 24 came the first grasses and first primates.
– First hominids came New Year’s Eve.
– Homo Sapiens arrived one hour before midnight.
– Age of written history equals last minute of the year.
• If geologic time examined in context of cliff one kilometer high (3300 ft.), an
individual’s existence would equal less than the thickness of the finest hair.
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17. Scale and Pattern
• An Example of Scale
– Text offers an example of different perspectives of scale, from
largest scale of ordinary human experience, walking though a
landscape, to driving thorough it, to flying over it, to satellite
viewpoint, then to smallest scale, from perspective of
spacecraft.
• The Pursuit of Pattern
1. Orderly patterns of distribution are much more difficult to discern
in geomorphology than in other geographic elements, such as
climate.
2. Overall, global distribution of topography is very disordered and
irregular.
3. Comprehending process (dynamics of topographic
development) more important than study of landform
distribution.
• The Pursuit of Pattern
– Patterns in the
distribution of landforms
are difficult to discern.
– Geomorphology
concentrates less on
distribution and more on
process.
– Fig. 13-27
Scale and Pattern
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