Chapter 22
Earth’s Interior
22.1 Earth’s Structure
• Scientists can’t see into Earth
• We can listen (earthquakes as sound waves)
• Or, 12 km holes (about 8 miles) can be drilled
for use in analysis
The Science of Geology
• Geology- the study of planet Earth, including its
composition and structure
• Geologist study geology
• Constructive forces vs. destructive forces
– Constructive forces shape the surface by building mountains,
etc.
– Destructive forces wear away mountains, etc.
• Uniformitarianism- geologic processes that happen today
happened in the past. This was defined by James Hutton in
the late 1700’s, a physician and farmer who studied rocks
he could only explain if they were older than other people
thought, and that they came from other rocks. This means
that mountains and canyons happen over a long time.
A Cross Section of Earth
• Earth has three layers of different density
– Crust
– Mantle
– Core
Crust
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Rocky outer layer
Thinnest
Made of silicates (Si and O, maybe Al, Fe, Ca)
Two types of crust
– Continental
» Less dense
» Made of granite
» ~40 km thick
– Oceanic
» Dense
» Made of basalt
» 7 km thick
Mantle
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Thick layer of hot, solid rock
2850 km
P and T increase closer to the core
Silicates, Fe, Mg
Three layers
– Lithosphere- cool, rigid rock, uppermost layer, 100 km thick
– Asthenoshpere- softer, weaker rock, taffy-like motion
– Mesosphere- stronger rock nearest core
Core
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Fe, Ni
3.6 million times normal pressure
5500 degrees Celsius
Outer core- high T, liquid metal, magnetic and electric
current source
• Inner core- high P, solid
22.2 Minerals
• Emeralds green from Cr
• Rock- solid combination of minerals or mineral materials
• Mineral- naturally occurring, inorganic solid with crystal
structure and characteristic chemical composition
• Inorganic- not made from living things (coal is organic since
it’s from plants)
• Concrete is not a mineral- man-made
• Minerals are the building blocks of rocks
• 4,000 minerals, but only a few are common, like quartz,
feldspar, mica, hornblende (granite)
• Crystal- repeating pattern of atoms
Properties of Minerals
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Crystal structure
Color
Streak
Luster
Density
Hardness
Fracture
Cleavage
Crystal Structure
• Geometric shape
• Some large, some small crystals, but all same
shape for a certain mineral
• Prisms, cubes, sheets, needles, threads
• Halite (table salt) is cubic
• Garnet (Jan.) is 12 sided (octahedral)
Color
• Pyrite (fool’s gold) is golden yellow
• Sulfur is yellow
• Quartz can take in different chemicals and be
different colors
Streak
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Color of mineral’s powder
Scrape on porcelain, or streak plate
Not always same as color of mineral
Hematite (black) has a red streak
Luster
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Way mineral reflects light
Shiny
Galena and pyrite metallic luster
Sulfur resinous-to-greasy luster
Rough is called earthy
Silky, pearly, vitreous (glassy)
Density
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D = m/v
High atomic mass means high density
P. 667 table
We’ll do calculations in lab experiments
Hardness
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Resistance to scratching
Hard scratches soft
Mohs hardness scale 1-10
Talc to diamond
Fingernail is 2.5
Fracture and Cleavage
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Fracture is a break, some are even, some not
Cleavage is an even break
Graphite (pencils)
Glass (uneven)
22.3 Rocks and the Rock Cycle
• 3 types of rocks
– Igneous- formed from magma (molten rock and gases)
which turns into lava. The rock occurs when it cools.
Intrusive rocks are coarse and large. Extrusive are smooth,
small. They are usually dark in color.
– Sedimentary- made from weathered or broken rocks,
found in oceans, lakes, streams, deserts
• Clastic- broken pieces held by cement
• Chemical- chemical reactions, like evaporation or acid rain
• Organic- ex. coral
– Metamorphic- changes form, P or T. Particles lined up
maybe bands (foliated rock)
– Rock cycle
22.4 Plate Tectonics
• Theory that lithosphere moves slowly on
asthenosphere.
• Continental drift (Earth as puzzle)
• Alfred Wegener and Pangaea
• Mid-ocean ridge- underwater mountains
• Sea-floor spreading- process by which new oceanic
crust is created at mid-ocean ridges as older crust
moves away
• Subduction- plates sink into mantle
• Trench- depression
• Evidence of movement of mantle (magnetic stripes)
Plate Boundaries
• Divergent- plates move away, magma flows
• Convergent- plates come together, mountain
• Transform- plates slide past (earthquake)
22.5 Earthquakes
• Earthquake- movement of lithosphere that occurs when rocks in
lithosphere suddenly shift, releasing stored energy in vibrations called
seismic waves
• Caused by stress in plate movement
• Fault- break in a mass of rock along which movement occurs ex. San
Andreas
• Fold- a bend in layers of rock
• Focus- center of earthquake beneath Earth
• Epicenter- center of earthquake on Earth’s surface
• P waves- longitudinal waves like sound waves (accordion), first detected
• S waves- transverse waves, can’t travel through liquid
• Surface waves- when seismic waves reach Earth’s surface, slower than P
and S, but larger ground movement
• Measured by seismograph using Richter Scale (most well known), Moment
Magnitude Scale (best), or Modified Mercalli Scale (observations)
22.6 Volcanoes
• Volcano- mountain that forms when magma reaches the
surface
• Most inactive
• Like a soda bottle
• Magma goes from magma chamber, to pipe, to vent, or
opening
• Top is called a crater, unless collapsed, which is a caldera
• Quiet if very hot, low in silica; high silica is loud
• Most on plate boundaries (Ring of Fire)
• Hot spot- region where hot rock extends from deep within
the mantle to the surface
Types of Volcanoes
• Shield- quiet, wide, flat
• Cinder Cone- ash and cinder, steeple
• Composite- explosive (traditional), lava and
ash