Chapter 13: Introduction to
Landform Study
The Structure of Earth
• Understanding of Earth’s structure based on minute
fraction of total depth (<8 miles)
• Good deal of understanding inferred by geophysical
means
• 4 regions
of Earth’s
interior
Figure 13-1
The Structure of Earth
• Crust
– Thinnest layer
• Depth of 5 km below ocean to near 20
km below land
• < 1% of Earth’s volume, 0.4% of
Earth’s mass
– Base
• Moho discontinuity
– Composed of mostly
silicate material
– Part of lithosphere
– Ocean crust (basalt) vs.
Continental crust (granite)
The Structure of Earth
• Mantle
– Largest and thickest layer
• Makes up 84% of total volume, 67% of total mass
• Extends to depth of
2900 km (1800 miles)
– Magnesium with
material from both
crust & core
– 3 sublayers
• Lithosphere (upper mantle)
– Cool/brittle rock
• Asthenosphere
– Plastic quality of rocks
• Lower mantle
– Rigid/brittle rock
The Structure of
Earth
• Core Composition: Iron & Nickel
• Outer/inner core combined = 15% of
Earth’s volume & 32% of Earth’s mass
• Outer core
– Molten (liquid), extends to
depth of 5000 km
– Generates Earth’s
magnetic field
• Magnetic poles not the
same as the axial poles
• Inner core
– Solid, dense mass
– Rotates independently
The Structure of Earth
• “Continental drift”
• Plate tectonics—large lithospheric plates slide along the
top of the
asthenosphere
The Composition of Earth
• Minerals—naturally formed compounds & elements of
Earth
• Characteristics
–
–
–
–
Solid
Found in nature
Inorganic
Specific chemical
composition
– Specific crystal
structure
• Atoms arrange in
patterns to form
crystals
The Composition of
Earth
• Important crustal minerals
– Silicates—oxygen + silicon
• Most common elements in the lithosphere
–
–
–
–
Oxides—oxygen + another element
Sulfides—sulfur + another element
Sulfates—sulfur + oxygen
Carbonates—light-colored minerals
composed of carbon, oxygen +
another element (i.e., limestone)
– Halides—derived from word “salt”,
salty minerals
– Native elements—gold and silver
• Also appear as elements
Figures 13-2 & 13-3
The Composition
of Earth
• Earth’s composition as a
whole
– Primarily iron & oxygen.
– Silicon is abundant in the
crust
– Iron & Magnesium are more
abundant in the lower mantle
& core due to density
9
The Composition of Earth
• Composition of Earth’s crust is significantly different from Earth
as a whole.
The Composition of Earth
• Rocks—composed of 2 or more minerals
– Fewer than 20 minerals make up 95% of the composition
of crustal rocks
– Bedrock
• Solid rock; no weathering
– Outcrop
• Bedrock exposure
– Regolith
• Partially weathered rock
– Petrology—
characteristics of
different rocks
Figure 13-4
The
Composition
of Earth
• Igneous rocks
– Igneous—“fiery
inception”
• Crystallized magma/lava
– Magma—molten rock
beneath Earth’s
surface
– Lava—molten rock on
Earth’s surface
– Pyroclastics
The Composition of Earth
• Igneous Rock Classification
– 2 Compositions
• Light colored (felsic)
• Dark colored (mafic)
– 2 Textures
• Plutonic (intrusive)
– Rocks cool slowly beneath
Earth’s surface
– Coarse-grained
• Volcanic (extrusive)
– Rocks cool rapidly on Earth’s
surface
– Fine-grained
The Composition of Earth
Figure 13-6
The Composition of Earth
Silica Content of Magma
Basalt
45-50% SiO2
Andesite
60% SiO2
Rhyolite
70-75% SiO2
The Composition
of Earth
• Sedimentary Rocks
– Sediments
– Lithification
• Putting fragments back together
• Compaction
• Cementation
– Iron oxide, silica & calcium
carbonate
– Deposited in layers
– Clastic Rocks
• Pieces of other rock
– Chemical Rocks
• Precipitated materials
– Organic Rocks
• Plant or animal parts
Figures 13-9 & 13-13
The Composition of Earth
• Metamorphic Rocks
– Re-crystallizing pre-existing
rock
– Heat and pressure
– Foliation
• Banded, layered, or wavy
characteristic after extreme
pressure
– Types
•
•
•
•
•
Contact metamorphism
Regional metamorphism
Burial metamorphism
Shock metamorphism
Pyro-metamorphism
Figure 13-16b
Quartzite comes from sandstone
18
Slate comes from of shale
The Composition of Earth
Metamorphic Rocks
hornblende
stress
Granite (igneous)
stress
Gneiss (metamorphic)
The Composition of Earth
• Rock cycle—processes where rocks transition from
igneous rocks to sedimentary rocks to metamorphic rocks
– Not a linear path
Figure 13-17
The Composition of Earth
• Continental rocks
– Sedimentary rocks =
75% of continents
– Continental crust: sial
• Granite
• Ocean floor rocks
– Ocean floor crust: sima
• Basalt
– More dense than
continental rocks =
subduction
Figures 13-18 & 13-19
The Composition of Earth
• Isostasy: equilibrium between gravity & buoyancy
Weight of rocks / glaciers / sediments on continental shelf
Earth’s Surface
Adjustment in the density of the asthenosphere
Figure 13-20
The Study of Landforms
• Topography vs. Landform
• Elements of landform study
– Structure
• Geology
– Process
• Actions creating landforms
– Slope
– Drainage
– Relief
• Change in elevation in an area
• Fundamental questions of geographic inquiry:
– What, where, why, and so what?
Figure 13-22
The Study of Landforms
Topography – Nebraska
24
The Study of Landforms
Topography
– Wyoming
25
Some Critical
Concepts
• Internal and External
Geomorphic Processes
– Internal: inside Earth, increase relief
– External: outside Earth; decrease
relief
Figure 13-23
Some Critical Concepts
• Uniformitarianism
– “The present is the key
to the past”
– Processes which
shaped the landscape
of the past are the
same that will shape
the future
• Geologic time
– Vast periods of time
over which geologic
processes operate
– Geologic time in 1 year
Figure 13-24
Scale and Pattern
• The Pursuit of Pattern—major landform assemblages of
the world
Figure 13-26
Summary
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Earth’s structure is presumed based on geophysical research
Earth’s interior consists of four regions
Earth’s composition consists of elements or compounds of elements called minerals
Seven primary types of minerals exist
Rocks are composed of minerals
Igneous rocks are those formed by cooling and solidification of molten rock
Plutonic rocks are those which form within the Earth
Volcanic rocks form on the Earth’s surface
Sedimentary rocks form as a result of transport of mineral material by water
Two primary types of sedimentary rocks, clastic and chemical/organic sedimentary rocks
Metamorphic rocks are igneous or sedimentary rocks that have been drastically changed by heat
and/or pressure
The rock cycle is the transition cycle through the different rock types
Continental and ocean floor rocks possess different characteristics which are important in geophysical
processes
Isostasy is the recognition of the differences between continental crust, oceanic crust, and mantle
Landforms are characterized by structure, process, slope, and drainage
Internal and external geomorphic processes are responsible for the relief of Earth
Uniformitarianism allows us to use geologic time to infer what happened in the past based on the
present