Download The Composition of Earth

Chapter 2 Lecture
McKnight's
Physical Geography
Lectures
Chapter 13
An Introduction to
Landform Study
Modified by AJ Allred
for Geography 1000
Salt Lake Community College
Fall 2013
Andrew Mercer
Mississippi State University
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Learning Goals of This Chapter
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•
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•
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Describe the internal structure of Earth.
Describe Earth's magnetic field.
Define mineral, and explain why they are important.
Describe quartz, and explain its importance.
Differentiate between rock, bedrock, outcrop, and
regolith.
• Identify the three rock classes or families, and
explain how they form.
• Explain the classification of igneous rocks.
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Learning Goals of This Chapter
• Describe igneous rock textures, and explain their
relationships to magma and lava and the terms
intrusive and extrusive.
• Identify and describe four intrusive igneous rocks
and six extrusive igneous rocks.
• Explain the classification of sedimentary rocks.
• Explain the structure of sedimentary deposits.
• Identify and describe four detrital (clastic)
sedimentary rocks and four chemical and organic
sedimentary rocks.
• Explain the classification of metamorphic rocks.
• Explain the three types of metamorphism.
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Learning Goals of This Chapter
• Explain "fracking."
• Identify and describe four foliated metamorphic
rocks and four non-foliated metamorphic rocks.
• Explain the rock cycle and its significance.
• Differentiate between the continental and
oceanic rocks.
• Explain isostasy and its significance.
• Define topography, landform, and geomorphology.
• Explain how structure, process, slope, and drainage
act together to shape the landscape.
• Differentiate between internal and external
geomorphic processes.
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The Structure of Earth
• Understanding of Earth's
structure based on inference
•
(three) regions of Earth's
interior
Four
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The Structure of Earth
• Crust
– Depth of 5 km below ocean to near 20 km below land
– Less than 1% of Earth's volume, 0.4% of Earth's mass
• Mantle
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–
–
–
Extends to depth of 2900 km (1800 miles)
Largest of four shells
Makes up 84% of total volume, 67% of total mass
Three sublayers
• Lithosphere
• Asthenosphere
• Rigid rocks – lower mantle
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The Structure of Earth
•
Outer
core
– Molten, extends to depth of 5000 km
•
Inner
core
– Dense mass with radius of about 1450 km
– Primarily made of iron/nickel or iron/silicate
– Two zones combined make up 15% of Earth's volume and
32% of Earth's mass
– Magnetic field of Earth controlled by outer core
– Magnetic poles not the same as the axial poles
• Plate tectonics and the structure of Earth
• “Continental drift”
• Plate tectonics – continental-sized plates slide along
the asthenosphere
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The Composition of Earth
• Minerals – naturally
formed compounds and
elements of Earth
• Mineral characteristics
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–
–
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Solid
Found in nature
Inorganic
Specific chemical
composition
– Contains atoms that
arrange in patterns to
form crystals
Silicon-based – sandy sediment
“cooked” (metamorphed) into a
new crystal
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The Composition of Earth
• Important crustal
minerals
– Silicates – combine
oxygen and silicon, the
most common elements
in the lithosphere
– Oxides – elements that
are combined with oxygen
– Sulfides – sulfur and
another element
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The Composition of Earth
• Important crustal minerals (cont.)
– Sulfates – contain sulfur and oxygen
– Carbonates – light-colored minerals that are composed
of a combination of carbon, oxygen and an element
(e.g., limestone)
– Halides – derived from word “salt,” salty minerals
– Native elements – gold and silver
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The Composition of Earth
100 important native elements
combine to make 4,400
important mineral compounds
Fewer than 20 minerals make
up 95% of the composition of
crustal rocks
– Bedrock
– Regolith
– Soil
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Oxygen, iron, calcium,
sulfur, silicon, carbon,
aluminum, magnesium,
lithium, titanium, etc.
The Composition of Earth
• The three classes of rocks
Igneous
Sedimentary
Metamorphic
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The Composition of Earth
• Igneous rocks
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–
–
–
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Igneous – “fiery inception”
Magma – molten rock beneath Earth's surface
Lava – molten rock when it flows onto Earth's surface
Pyroclastics
Classification of igneous rocks is based on mineral
composition and texture
– Texture based on how rocks cool
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The Composition of Earth
• Two types of igneous
rocks
– Plutonic (intrusive)
• Rocks cool beneath Earth's
surface
• Surrounding rocks insulate
the magma intrusion,
slowing cooling
• Individual minerals in a
plutonic rock can grow to
large size
• Granite
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The Composition of Earth
• Two types of igneous
rocks (cont.)
– Volcanic (extrusive)
• Form on Earth's surface
• Cool rapidly
• Generally do not show
individual mineral crystals,
but can if the crystals are
formed from shattered rock
that was explosively ejected
• Basalt
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• Sedimentary Rocks
– External processes cause rock disintegration
– Material transported by water as sediment
– Over long periods, large amounts of sediment build to
large thicknesses
– Exert enormous pressure that causes particles in
sediment to interlock
– Chemical cementation takes place
– Strata – horizontal layers of sedimentary rock; sometimes
tilted into vertical by Earth processes
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Sedimentary rock
Slightly more durable cap rock protects these features
for a few “minutes” longer.
Arches National Park
Layered, cemented ‘dust’
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The Composition of Earth
• Two primary types of sedimentary rocks
– Clastic
• Composed of fragments of preexisting rocks
• Shale is an example (may host oil, gas, coal in ‘dust’ layers)
• Conglomerate; composed of pebble-sized fragments
– Chemical and organic sedimentary rocks
• Formed by precipitation of soluble materials or complicated
chemical reactions
• Limestone and coal are examples
• Organic sedimentary rocks such as coal form from remains
of dead plants and animals
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The Composition of Earth
• The two primary types of sedimentary rocks; white
rock is limestone, dark rock is shale
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• Metamorphic Rocks
– Rocks that were originally igneous or sedimentary and
have been changed by heat and pressure
– “cooking” of rocks “morph” into something different
– Rearranges the crystal structure of the original rock
– Contact metamorphism – rock contacts magma and is
rearranged
– Bones and shells (low in organics) turn into gypsum or
chalk  limestone  marble
– sandstone becomes quartzite (sort of like glass)
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The Composition of Earth
• Schist – metamorphic
rocks with narrow foliations
• Gneiss – broad, banded
foliations
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The Composition of Earth
• The rock cycle – processes where rocks can
transition between the three rock types
Chicken or egg?
“scissors,paper,
rock”
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• Continental and ocean floor rocks
– Sedimentary rocks make up 75% of the continents
– Continental crust – sial (silicon and aluminum)
– Ocean floor crust – sima (silicon and magnesium)
– Ocean crust can be subducted into the athenosphere
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The Composition of Earth
• Isostasy – push crust
down in one place – it
pushes back up in another
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– Internal – originate from
within Earth, increase relief
of land surface
– External – originate from
sources above the
lithosphere, such as the
atmosphere or oceans;
decrease relief of land
surface
© 2014 Pearson Education, Inc.
Both are energized by
different forms of
radioactivity