GEOLOGY: A Brief Primer Kavli Institute for Theoretical Physics Module 1 This is the first in a series of modules intended for use by teachers of physics and related sciences. They can be used as a tutorial and/or as ancillary materials in the classroom. They have been designed to supplement the various topics in physics. They are based on the 2014 CIDER (Cooperative Institute
Transcript
Slide 1
Kavli Institute for Theoretical PhysicsModule 1 This is the
first in a series of modules intended for use by teachers of
physics and related sciences. They can be used as a tutorial and/or
as ancillary materials in the classroom. They have been designed to
supplement the various topics in physics. They are based on the
2014 CIDER (Cooperative Institute for Deep Earth Research)
Conference and developed by the Teachers-In-Residence Program at
the KITP.
Slide 2
MODULAR 1 GEOLOGY: A BRIEF PRIMER GENERAL OBJECTIVES: 1. To
introduce students to the major concepts of geology. 2. To
introduce the basic internal structure of the Earth and its
associated terminology. 3. To introduce some basic physics-related
concepts that govern the dynamics of the internal structures of the
Earth, historically to the present day. 4. To introduce the
parameters that drive the motions, energy flow, from deep within
the planet to the surface, and the consequences that result.
Slide 3
Pre-Modular Questions:
Slide 4
1. Most of the Earths mass consists of liquid water. (T/F)
Slide 5
Pre-Modular Questions: 1. Most of the Earths mass consists of
liquid water. (T/F) 2. The core of the Earth is approximately as
large as the Moon. (T/F)
Slide 6
Pre-Modular Questions: 1. Most of the Earths mass consists of
liquid water. (T/F) 2. The core of the Earth is approximately as
large as the Moon. (T/F) 3. The Earth is more dense than the planet
Jupiter. (T/F)
Slide 7
Pre-Modular Questions: 1. Most of the Earths mass consists of
liquid water. (T/F) 2. The core of the Earth is approximately as
large as the Moon. (T/F) 3. The Earth is more dense than the planet
Jupiter. (T/F) 4. The geometric center of the Earth is so hot, and
the pressure is so great that iron there exists as a liquid.
(T/F)
Slide 8
Pre-Modular Questions: 1. Most of the Earths mass consists of
liquid water. (T/F) 2. The core of the Earth is approximately as
large as the Moon. (T/F) 3. The Earth is more dense than the planet
Jupiter. (T/F) 4. The geometric center of the Earth is so hot, and
the pressure is so great that iron there exists as a liquid. (T/F)
5. The deepest interior of the Earth is as hot as the surface of
the Sun. (T/F)
Slide 9
Question, What does the inside of an avocado have in common
with the interior of the Earth?
Slide 10
Question, What does the inside of an avocado have in common
with the interior of the Earth? Answer: They look very
similar!
Slide 11
An avocado has an outer skin
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An avocado has an outer skin The inner flesh
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An avocado has an outer skin The inner flesh And an inner
seed
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The Earth has:
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An outer crust
Slide 16
The Earth has: An outer crust A mantle
Slide 17
The Earth has: An outer crust A mantle And a core
Slide 18
The Earth has: An outer crust A mantle And a core *outer
Slide 19
The Earth has: An outer crust A mantle And a core *outer
*inner
Slide 20
The Earth has: An outer crust A mantle And a core *outer *inner
An avocado has an outer skin The inner flesh And an inner seed See
the similarity???
Slide 21
The Earth has: An outer crust A mantle And a core *outer *inner
An avocado has an outer skin The inner flesh And an inner seed See
the similarity??? Of course, theres much more to it than that!
Slide 22
The Earths layers are not static (like an avocado). Besides
revolving on its axis, once every 24 hours, and revolving around
the sun, every 365 days, the interior of the Earth is a dynamic
structure, subtle, but prone to a variety of motions that can cause
interesting (and sometimes devastating) effects!
Slide 23
The Earths layers are not static (like an avocado). Besides
revolving on its axis, once every 24 hours, and revolving around
the sun, every 365 days, the interior of the Earth is a dynamic
structure, subtle, but prone to a variety of motions that can cause
interesting (and sometimes devastating) effects! But first, lets
look at some details about these layers.
Slide 24
The Earths mass is 5.98 x 10 24 kg. Although it is one of the
smallest and least massive of the planets in our solar system, it
is one of the most dense planets, with an average density of 5.52
g/cc. (Compare to Jupiter whose density is 1.33 g/cc, or Saturn:
0.687 g/cc)!
Slide 25
The Earths mass is 5.98 x 10 24 kg. Although it is one of the
smallest and least massive of the planets in our solar system, it
is one of the most dense planets, with an average density of 5.52
g/cc. (Compare to Jupiter whose density is 1.33 g/cc, or Saturn:
0.687 g/cc)! However, as you can see, variations in mass means that
the density of the different layers can vary, leading to a dynamic
system capable of transmitting energy in several ways, having to do
with their composition, temperature, and pressure. (These
parameters will be treated in other modules.)
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The depth of each layer is given in the chart below. The Earth
is held together by gravitational forces that keep the Earth from
breaking apart. However, like going deeper into water, these forces
increase with depth, thus increasing the pressure as you go deeper
into the Earth.
Slide 27
The depth of each layer is given in the chart below. The Earth
is held together by gravitational forces that keep the Earth from
breaking apart. However, like going deeper into water, these forces
increase with depth, thus increasing the pressure as you go deeper
into the Earth. Increased pressures means increased
temperatures!
Slide 28
Here is what the temperature range of the various layers looks
like. Temperature and pressure deviations are used to define
subdivisions in our basic layers, indicating a transition from one
layer to another. The Crust and Rigid part of the Upper Mantle are
known as the LITHOSPHERE. The liquid (or flowing) part of the Upper
Mantle just below the lithosphere is called the ASTHENOSPHERE. This
is then followed by a semi-rigid layer, which defines the inner
(LOWER) MANTLE. The Molten Outer Core extends nearly 2000 km
beneath that, followed by A SOLID INNER CORE! (Roughly about the
size of the Moon!) As hot as the surface of the sun is, the center
of the Earth is just as hot!
Slide 29
Here is what the temperature range of the various layers looks
like. Temperature and pressure deviations are used to define
subdivisions in our basic layers, indicating a transition from one
layer to another. The Crust and Rigid part of the Upper Mantle are
known as the LITHOSPHERE. The liquid (or flowing) part of the Upper
Mantle just below the lithosphere is called the ASTHENOSPHERE. This
is then followed by a semi-rigid layer, which defines the inner
(LOWER) MANTLE. The Molten Outer Core extends nearly 2000 km
beneath that, followed by A SOLID INNER CORE! (Roughly about the
size of the Moon!) These seemingly alternating layers of liquids,
moltens, and solids indicate that the physical and chemical
composition of these substances must vary accordingly.
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So, how do we know all this?
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Echo-sounding techniques are used to explore the Earth's crust.
Images, similar to sonograms, are produced. A sonogram in the crust
is called a seismic reflection. Seismic waves from "small
explosions or thumper trucks" return echoes from rock layers.
Seismographs pick up these echoes. The Earths crust is the
outermost layer of the Earth. It is covered with continental crust
and oceanic crust. Rising plumes of heat from the Earth's core
cause the plates* to move. The convection currents cause the plates
to collide and move apart. Other plates move horizontally past
another plate. All plate movement at these boundaries cause both
large and small earthquakes. *A plate is a massive, irregularly
shaped slab of solid rock, generally composed of both continental
and oceanic lithosphere
Slide 33
How do these massive slabs of solid rock float despite their
tremendous weight? The answer lies in the composition of the rocks.
Continental crust is composed of granitic rocks which are made up
of relatively lightweight minerals such as quartz and feldspar. By
contrast, oceanic crust is composed of basaltic rocks, which are
much denser and heavier. The variations in plate thickness are
nature's way of partly compensating for the imbalance in the weight
and density of the two types of crust. Because continental rocks
are much lighter, the crust under the continents is much thicker
(as much as 100 km) whereas the crust under the oceans is generally
only about 5 km thick. Like icebergs, only the tips of which are
visible above water, continents have deep "roots" to support their
elevations. PLATES
Slide 34
PLATE TECTONICS The word tectonics comes from a Greek word
meaning to build. Tectonic plates are huge moving slabs that
together make up Earths outer layer. Some span thousands of miles.
In all, a dozen major plates cover Earths surface.
Slide 35
Plates migrate atop Earths mantle. Think of the mantle as the
top of the flesh of an avocado (but much hotter!!). Temperatures
there range from 1,000 to 3,700 Celsius (about 1,800 to 6,700
Fahrenheit). The density of oceanic plates are approximately 3.3
grams per cubic centimeter. Continental crust is only 2.7 grams per
cubic centimeter. When these two different types of plates meet the
oceanic plate bends and begins to slip underneath the lighter
continental plate forming a trench between the plates where they
meet. Density is why the continental crust always overrides the
heavier oceanic crust. The oceanic crust melts as it forced
downward beneath the continental crust. The rocks are recycled and
form new igneous rocks when volcanoes erupt.
Slide 36
How Plate Tectonics Works: 1. There are two basic types of
LITHOSPHERE: continental and oceanic. CONTINENTAL lithosphere has a
low density because it is made of relatively light- weight
minerals. OCEANIC lithosphere is denser than continental
lithosphere because it is composed of heavier minerals. A plate may
be made up entirely of oceanic or continental lithosphere, but most
are partly oceanic and partly continental.
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How Plate Tectonics Works: 2. Beneath the lithospheric plates
lies the ASTHENOSPHERE, a layer of the mantle composed of denser
semi-solid rock. Because the plates are less dense than the
asthenosphere beneath them, they are floating on top of the
asthenosphere.
Slide 38
How Plate Tectonics Works: 3. Deep within the asthenosphere the
pressure and temperature are so high that the rock can soften and
partly melt. The softened but dense rock can flow very slowly
(think of Silly Putty) over geologic time. Where temperature
instabilities exist near the core/mantle boundary, slowly moving
convection currents may form within the semi-solid
asthenosphere.
Slide 39
How Plate Tectonics Works: 4. Once formed, convection currents
bring hot material from deeper within the mantle up toward the
surface.
Slide 40
How Plate Tectonics Works: 5. As they rise and approach the
surface, convection currents diverge at the base of the
lithosphere. The diverging currents exert a weak tension or pull on
the solid plate above it. Tension and high heat flow weakens the
floating, solid plate, causing it to break apart. The two sides of
the now-split plate then move away from each other, forming a
DIVERGENT PLATE BOUNDARY.
Slide 41
How Plate Tectonics Works: 6. The space between these diverging
plates is filled with molten rocks (magma) from below. Contact with
seawater cools the magma, which quickly solidifies, forming new
oceanic lithosphere. This continuous process, operating over
millions of years, builds a chain of submarine volcanoes and rift
valleys called a MID-OCEAN RIDGE or an OCEANIC SPREADING
RIDGE.
Slide 42
How Plate Tectonics Works: 7. As new molten rock continues to
be extruded at the mid-ocean ridge and added to the oceanic plate
(6), the older (earlier formed) part of the plate moves away from
the ridge where it was originally created.
Slide 43
How Plate Tectonics Works: 8. As the oceanic plate moves
farther and farther away from the active, hot spreading ridge, it
gradually cools down. The colder the plate gets, the denser
(heavier) it becomes. Eventually, the edge of the plate that is
farthest from the spreading ridges cools so much that it becomes
denser than the asthenosphere beneath it.
Slide 44
How Plate Tectonics Works: 9. As you know, denser materials
sink, and thats exactly what happens to the oceanic plateit starts
to sink into the asthenosphere! Where one plate sinks beneath
another a subduction zone forms.
Slide 45
SUBDUCTION: the driving force behind plate tectonics.
Slide 46
How Plate Tectonics Works: 10. The sinking lead edge of the
oceanic plate actually pulls the rest of the plate behind
itevidence suggests this is the main driving force of subduction.
Geologists are not sure how deep the oceanic plate sinks before it
begins to melt and lose its identity as a rigid slab, but we do
know that it remains solid far beyond depths of 100 km beneath the
Earths surface.
Slide 47
How Plate Tectonics Works: 11. Subduction zones are one type of
CONVERGENT PLATE BOUNDARY, the type of plate boundary that forms
where two plates are moving toward one another. Notice that
although the cool oceanic plate is sinking, the cool but less dense
continental plate floats like a cork on top of the denser
asthenosphere.
Slide 48
How Plate Tectonics Works: 12. When the subducting oceanic
plate sinks deep below the Earths surface, the great temperature
and pressure at depth cause the fluids to sweat from the sinking
plate. The fluids sweated out percolate upward, helping to locally
melt the overlying solid mantle above the subducting plate to form
pockets of liquid rock (magma).
Slide 49
How Plate Tectonics Works: 13. When the subducting oceanic
plate sinks deep below the Earths surface, the great temperature
and pressure at depth cause the fluids to sweat from the sinking
plate. The fluids sweated out percolate upward, helping to locally
melt the overlying solid mantle above the subducting plate to form
pockets of liquid rock (magma).
Slide 50
How Plate Tectonics Works: 14. Some of the molten rock may
reach the Earths surface to erupt as the pent- up gas pressure in
the magma is suddenly released, forming volcanic (extrusive) rocks.
Over time, lava and ash erupted each time magma reaches the surface
will accumulatelayer upon layerto construct volcanic mountain
ranges and plateaus, such as the Cascade Range and the Columbia
River Plateau (Pacific Northwest, U.S.A.).
Slide 51
Continental crust Continental crust is much older than oceanic
crust. The basement rocks of the continents are granitic rocks.
Granitic rocks are lighter than oceanic crust rocks. The minerals
that make up the crust are primarily quartz and feldspar. When two
crustal plates meet the continental crust is never destroyed.
Instead, it overrides oceanic crust or smashes together with
another continental crust to form great mountain chains. The
Himalaya Mountains are growing as the Eurasian Plate collides with
the Indian Plate and the Earths crust is not destroyed.
Slide 52
Continental Drift? So over eons, Earths surface has changed a
lot. For instance, roughly 250 million years ago, Earth had one
giant landmass: Pangaea.
Slide 53
Continental Drift? So over eons, Earths surface has changed a
lot. For instance, roughly 250 million years ago, Earth had one
giant landmass: Pangaea. Within some 50 million years, the plates
under that land and the ocean moved. Plate movement split Pangaea
into two huge continents, called Laurasia and Gondwanaland.
Slide 54
Continental Drift? So over eons, Earths surface has changed a
lot. For instance, roughly 250 million years ago, Earth had one
giant landmass: Pangaea. Within some 50 million years, the plates
under that land and the ocean moved. Plate movement split Pangaea
into two huge continents, called Laurasia and Gondwanaland. As
Earths plates kept moving, those landmasses each broke apart more.
As they spread and traveled, they evolved into our modern
continents.
Slide 55
Continental Drift? Although some people mistakenly talk about
continental drift, its the plates that move. Continents are just
the tops of plates that rise above the ocean. We see only the
continents atop the plates, just as sailors see only the tips of
icebergs at sea. Plates continue to glide slowly across Earths
mantle. As the plates move, expect the future placement of
continents and oceans to become completely reshuffled. The Atlantic
Ocean will open and close over cycles of 300 million to 500 million
years.
Slide 56
WHAT ABOUT EARTHQUAKES AND VOLCANOES??? 1906 EARTHQUAKE IN SAN
FRANCISCO The Indonesian volcano Anak Krakatau erupts at night
(credit: Getty Images/Tom Pfeiffer/VolcanoDiscovery)
Slide 57
WHAT ABOUT EARTHQUAKES AND VOLCANOES??? 1906 EARTHQUAKE IN SAN
FRANCISCO The Indonesian volcano Anak Krakatau erupts at night
(credit: Getty Images/Tom Pfeiffer/VolcanoDiscovery) How do Earths
GEODYNAMICS account for what happens on the surface???
Slide 58
WHAT ABOUT EARTHQUAKES AND VOLCANOES??? There are 20 moving
plates under the earths surface, when one of these plates slips
past the other; there is a sudden increase in pressure which
sometimes breaks the crust. This break in the crust helps releasing
the build up pressure in the energy form, which creates huge waves
and results in an earthquake. These waves are in the infrasonic
range of the human audio spectrum. That is, they are below the
audio (hearing) capability of humans.
Slide 59
WHAT ABOUT EARTHQUAKES AND VOLCANOES??? While the edges of
faults are stuck together, and the rest of the block is moving, the
energy that would normally cause the blocks to slide past one
another is being stored up. When the force of the moving blocks
finally overcomes the friction of the jagged edges of the fault and
it unsticks, all that stored up energy is released. The energy
radiates outward from the fault in all directions in the form of
seismic waves like ripples on a pond. The seismic waves shake the
earth as they move through it, and when the waves reach the earths
surface, they shake the ground and anything on it, like our houses
and us! Seismic waves are the waves of energy caused by the sudden
breaking of rock within the earth or an explosion. They are the
energy that travels through the earth and is recorded on
seismographs.
Slide 60
WHAT ABOUT EARTHQUAKES AND VOLCANOES??? There are several
different kinds of seismic waves, and they all move in different
ways. The two main types of waves are body waves and surface waves.
Body waves can travel through the earth's inner layers, but surface
waves can only move along the surface of the planet like ripples on
water. Earthquakes radiate seismic energy as both body and surface
waves.
Slide 61
WHAT ABOUT EARTHQUAKES AND VOLCANOES??? The first kind of body
wave is the P wave or primary wave. This is the fastest kind of
seismic wave, and, consequently, the first to 'arrive' at a seismic
station. The P wave can move through solid rock and fluids, like
water or the liquid layers of the earth. It pushes and pulls the
rock it moves through just like sound waves push and pull the air.
Have you ever heard a big clap of thunder and heard the windows
rattle at the same time? The windows rattle because the sound waves
were pushing and pulling on the window glass much like P waves push
and pull on rock. Sometimes animals can hear the P waves of an
earthquake. Dogs, for instance, commonly begin barking hysterically
just before an earthquake 'hits' (or more specifically, before the
surface waves arrive). Usually people can only feel the bump and
rattle of these waves.
Slide 62
P waves are also known as compressional waves, because of the
pushing and pulling they do. Subjected to a P wave, particles move
in the same direction that the the wave is moving in, which is the
direction that the energy is traveling in, and is sometimes called
the 'direction of wave propagation'. Lets look at how the P wave
moves:
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S Waves The second type of body wave is the S wave or secondary
wave, which is the second wave you feel in an earthquake. An S wave
is slower than a P wave and can only move through solid rock, not
through any liquid medium. It is this property of S waves that led
seismologists to conclude that the Earth's outer core is a liquid.
S waves move rock particles up and down, or
side-to-side--perpendicular to the direction that the wave is
traveling in (the direction of wave propagation). Lets see how an S
wave moves:
Slide 65
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Travelling only through the crust, surface waves are of a lower
frequency than body waves, and are easily distinguished on a
seismogram as a result. Though they arrive after body waves, it is
surface waves that are almost entirely responsible for the damage
and destruction associated with earthquakes. This damage and the
strength of the surface waves are reduced in deeper earthquakes.
The first kind of surface wave is called a Love wave, named after
A.E.H. Love, a British mathematician who worked out the
mathematical model for this kind of wave in 1911. It's the fastest
surface wave and moves the ground from side-to-side. Confined to
the surface of the crust, Love waves produce entirely horizontal
motion. Heres how a Love Wave moves:
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Slide 68
Rayleigh Waves The other kind of surface wave is the Rayleigh
wave, named for John William Strutt, Lord Rayleigh, who
mathematically predicted the existence of this kind of wave in
1885. A Rayleigh wave rolls along the ground just like a wave rolls
across a lake or an ocean. Because it rolls, it moves the ground up
and down, and side-to-side in the same direction that the wave is
moving. Most of the shaking felt from an earthquake is due to the
Rayleigh wave, which can be much larger than the other waves. Heres
how a Rayleigh Wave moves:
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Of course, earthquakes CAN be VERY DESTRUCTIVE, depending on
where they strike! They are most likely to occur at locations on or
near FAULT LINES, where plates meet.
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But earthquakes can also have other catastrophic
effects!!!
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SUCH AS TSUNAMIS!!
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And even VOLCANOES!!
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How???
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See how in modular #2 The Dynamics of Physics as demonstrated
inside Earth!
Slide 78
POST-MODULAR QUESTIONS:
Slide 79
1.The surface, or crust, of the Earth extends this far down: a.
70 km. b. 200 km. c. 500 km. d. 1000 km.
Slide 80
POST-MODULAR QUESTIONS: 2.The major interior layer between the
Earths crust and core is called the a. semi-rigid Layer. b. O Zone.
c. mantle. d. temperate zone.
Slide 81
POST-MODULAR QUESTIONS: 3.The primary composition of the
Continental Crust is ________ as compared to the Oceanic Crust. a.
made up of relatively light weight minerals b. made up of extremely
dense minerals c. the same d. molten
Slide 82
POST-MODULAR QUESTIONS: 4.Plates is a term used to describe a.
the continents of the Earth as we know them today. b. the bottom
layer of the Earths crust. c. massive, irregularly-shaped slabs of
solid rock. d. the basins that hold sea water.
Slide 83
POST-MODULAR QUESTIONS: 5.The word tectonics comes from a. the
English word technical. b. the Latin word for deep. c. the physics
term for sliding friction. d. The Greek word meaning to build.
Slide 84
POST-MODULAR QUESTIONS: 6.The number of plates that cover the
Earths surface is approximately a. 12 b. 53 c. 128 d. 2012
Slide 85
POST-MODULAR QUESTIONS: 7.Most plates are a. mostly Oceanic. b.
mostly Continental. c. partly Oceanic and partly Continental. d.
neither Oceanic nor Continental.
Slide 86
POST-MODULAR QUESTIONS: 8.Heat from deep within the Earth rises
toward the crust, causing the plates to move (very slowly) is due
primarily to a. convection. b. conduction. c. radiation. d.
subduction.
Slide 87
POST-MODULAR QUESTIONS: 9.The term for the geological process
by which the edge of one plate slides under the edge of an adjacent
plate is called a. crusting. b. abduction. c. transition. d.
subduction.
Slide 88
POST-MODULAR QUESTIONS: 10.The phrase Continental Drift a.
describes the actual movements of the continents over eons of time.
b. is misleading, since the continents do not drift, the plates
move. c. is a measure of the water flow patterns on the surface of
the Earth. d. Is used to describe the motion of molten crust after
an external impact.
Slide 89
POST-MODULAR QUESTIONS: 11.The Atlantic Ocean will a. open and
close over cycles of 300 to 500 million years. b. eventually
evaporate due to increased heat from the core of the Earth. c. In
time drain into the major Atlantic Fault Line. d. remain much the
same indefinitely.
Slide 90
POST-MODULAR QUESTIONS: 12.The frequencies of seismic waves
passing between layers of the mantle and crust a. are mainly
ultrasonic. b. are mainly infrasonic. c. are mainly with the human
audio frequency range. d. are inaudible, since they do not generate
sound waves.