Transcript lecture 01s - Kean University

Introduction To Geology

Geology is the study of the Earth

Materials

Phenomena and Processes

Life
Lava Lamp
Meteorite
magnets, glass plate, iron chips
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Scientific Method

Hypothetico-deductive framework
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Hypotheses have testable consequences
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We test hypotheses to try to falsify them
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Karl Popper
http://en.wikipedia.org/
wiki/Karl_Popper
1934 Popper Logic of
Scientific Discovery
Popper: Hypotheses
In Science are
2
Falsifiable
Paradigm: a supermodel with
unexpected predictive power
http://en.wikipedia.org/wiki/Thomas_Kuhn
http://www.amazon.com/StructureScientific-Revolutions-ThomasKuhn/dp/0226458040/ref=pd_cp_b_1
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Early Geological Concepts

Catastrophism
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Flood, Earthquake, Tsunamis, Meteors
Uniformitarianism
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Present is key to past, slower processes
Erosion, deposition, mountains, glaciers
James Hutton (1726-1797)
Championed by Charles Lyell
Notice these are early Paradigms
4
Modern Synthesis
The
Plate Tectonics Paradigm
Uniformitarian and slow
•Mass Extinctions
Sudden Catastrophes
•Both are correct
A 6-7 km meteor hit Yucatan ~65 mya;
major extinction event
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Origin of the Universe

The spectral shift of light coming from
distant galaxies tells us that the universe is
expanding* out of a very small volume
began about 13.7 bya
An object moving away
shifts the absorption
line toward the red.
An object moving
toward you shifts the
line toward the violet

Yellow-green
absorption line of
Helium, wavelength
587 nanometers
The universe expanded from a state of pure
energy, hydrogen atoms evolved through a
process called nucleosynthesis
* Distant objects are red-shifted
http://en.wikipedia.org/wiki/Redshift
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Element: an atom with a certain number of Protons, e.g. Oxygen has 6
Carbon has 8
Origin of the Elements

Hydrogen gas clouds condensed to form
main sequence stars.
Hydrogen burning forms Helium

Main sequence stars form Oxygen and
Carbon. 3 Heliums make 1 Carbon
Fred Hoyle
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Water = 2 Hydrogen + 1 Oxygen
Origin of Heavy Elements
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
A star more than 9 times the mass of our sun
burns faster, then expands into a red super
giant star. Betelgeuse, for example.
Pressure is high enough to also produce the
heavier elements including silicon,
magnesium, and iron.
Once its fuel is exhausted,
a supernova explosion *occurs

due to core collapse.
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*one of many ways
Origin of Our Solar System

Our solar system with its abundant collection
of heavier elements condensed from the gas
cloud left after the explosion of a supernova.
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Supernova ejects matter
rich pressure waves into
space
Local concentrations of
dust coalesce
Balance between gravity
and solar wind
For low speeds
Force = mass x acceleration
F= ma
Energy = Force x distance
E = mass x accel x distance
It takes more energy to move
a more massive atom, and/or
to move an atom a greater
distance
Which is why heavy Silicon,
Oxygen and Iron planets
are near the sun, and lighter
Hydrogen Helium planets
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are further away
1.During coalescence:
1_7
Particles
assemble
due to gravity –
heat up CLAP HANDS
3.DIFFERENTIATION
Iron melts and
begins to sink
4.
5.
Lighter materials
concentrate
closer to surface
6. Crust and Mantle Crust and
Silicate Minerals
7. Core Iron and
Nickel; liquid
outer core, solid
inner core
mantle
2.Planetesimals
strike growing
Earth
2bThe moon
formed after a
Mars-sized planet
hit earth, about
4.6 bya
We use that event
as Earth’s origin
date
8. Interior of
Earth is hotter
than surface
Liquid
core
Atmosphere
Crust
Mantle
Outer core
Inner core
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Earth’s Internal Structure
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Earth’s internal layers defined by
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Chemical composition
Physical properties
Deduced from Seismographs of Earthquakes
Meteorites lend support
Layers defined by composition
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Crust
Mantle
Core
Iron-Nickel Meteorite
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The density of Earth’s Layers
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“Three centuries ago, the English scientist
Isaac Newton calculated, from his studies of
planets and the force of gravity, that the
average density of the Earth is twice that of
surface rocks and therefore that the Earth's
interior must be composed of much denser
material. “
http://pubs.usgs.gov/gip/interior/
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Earth’s internal structure

Main layers of Earth are based on physical properties
including mechanical strength

Outer layers mostly Silicate Minerals: Crust and Mantle
 Lithosphere (behaves like a brittle solid)
Crust and uppermost mantle
 Asthenosphere “weak sphere”
Rest of Upper Mantle
Heat softened, plastic solid
 Lower Mantle
Solid due High Pressures
• Inner Layers Core Iron and Nickel,
outer above melting point - liquid,
inner solid due to high pressures
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1_8
CRUST
(least dense)
Upper mantle
Continental crust
Oceanic crust
MANTLE
0 km
~100 km
~350 km
Lower mantle
Lithosphere
Asthenosphere
CORE
(most dense)
Outer
core
~5155 km
Inner
core
~2900 km
Earth’s center is 6371 kilometers
below the surface, 1 mi = 1.61 km.
Equals ~ 3957 miles, or about
4000 miles radius
6371 km x 1 mile/1.61 km = 3957 miles
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http://pubs.usgs.gov/gip/interior/
“Although the core and mantle are about equal in thickness,
the core actually forms only 15 percent of the Earth's
volume, whereas the mantle occupies 84 percent. The crust
makes up the remaining 1 percent. “
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There are three types of Rock
IGNEOUS – From molten rock
SEDIMENTARY – From rock
fragments deposited in water and
cemented together. Also from
precipitates.
METAMORPHIC – Rocks altered
by heat, pressure, chemical
reactions
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Sediment
Rock Cycle
Each type can be formed from any other
Weathering,
transport, and
deposition
IGNEOUS
ROCK
Cementation and compaction
Heat and
pressure
(metamorphism)
Weathering,
transport,
and
deposition
Cooling and
Solidification
(crystallization)
SEDIMENTARY
ROCK
Heat and
pressure
(metamorphism)
1_11
Melting
Magma
(molten rock)
METAMORPHIC
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ROCK
1_14
Humans a very recent event
Note extinctions end of Permian and Cretaceous
Modern humans
Extinction of dinosaurs, others, 75%
Flowering plants and grasses
First mammals
Earliest dinosaurs
Extinction of Trilobites,
many others. 83%
genera
Early reptiles
Primitive
fish
Memorize the Periods
and dates when Eras start & end
Use Timescale doc, which is
simplified
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The Geology Paradigm
The continents fit together
WW II sonar reveals
mid-ocean ridge
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Continental drift: An idea
supported with tests
Why do the continents fit together?

Alfred Wegener
Summarized evidence in 1915
 Published The Origin of
Continents and Oceans
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Wegener’s Continental drift hypothesis
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Supercontinent Pangaea began breaking
apart about 200 million years ago
This hypothesis is testable
http://en.wikipedia.org/wiki/Alfred_Wegener
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Wegener’s Continental drift hypothesis
Continents "drifted" to present positions
Evidence used in support of continental
drift hypothesis:
Fit of continents
Fossil evidence
Rock type and mountain belts
Paleoclimatic evidence
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Fit of Continents: Pangaea
approximately 200 million years ago
Especially good agreement if continental shelf is included.
Coastlines Fit
Mountain Ranges line up
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Fossil Evidence
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Fossil Reptiles similar in South Africa,
Antarctica, South America and India
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Fossil Plants also very similar
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More about this later
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Matching of
mountain
ranges
on continents
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Paleoclimatic evidence for Continental
Drift
Ancient glaciers
line up if continents
together
26
Arthur Holmes


Wegener had no mechanism.
Arthur Holmes proposed that Earth's mantle
contained convection cells that dissipated
radioactive heat and moved the crust at the
surface
27
Some useful
background
Common lavas
contain the mineral
Magnetite
Magnetite crystals
align with earth’s
magnetic field
Gives us latitude
where the lava
“froze”
ALSO
“North” and “south”
reverse at irregular
intervals
Good for aligning
events worldwide28
The revolution begins
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
During the 1940s and 1950s technological
advances permitted mapping of the ocean
floor. There are mountain ranges in the centers
of oceans.
Seafloor spreading hypothesis was proposed
by Harry Hess in the early 1960s.
http://www.amnh.org/education/resources/rfl/web/essaybooks/earth/p_hess.html
Harry kept his depth sounder on, collected huge amounts of data. Together, the data
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show mid-ocean ridges.
Harry Hess: Mid-ocean ridges are spreading apart due to flow in
the mantle. Crust moves apart as if on conveyer belts.
Note Mid-ocean Ridges
(aka MORs)
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How can we test the hypothesis?

Fred Vine and Drummond Matthews: How
about geomagnetic reversals?

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Earth's magnetic field reverses polarity at
irregular intervals– north magnetic pole
becomes south magnetic pole, and vice versa
Dates when polarity of Earth’s magnetism
changed were determined from lava flows
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Paleomagnetic reversals recorded by
new lava rock at mid-ocean ridges
This common lava
rock is called
“Basalt”
SHOW SAMPLE
The Magnetite crystals
align with the magnetic
field, forming large bands
of north-pointing or southpointing ocean floor.
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Geomagnetic reversals
Geomagnetic reversals are recorded
in the ocean crust when hot lava
solidifies. Magnetic minerals point to
poles
In 1963 Fred Vine and Drummond
Matthews pointed out that
symmetrical magnetic stripes in the
ocean crust near ridges were
predicted by Hess’s concept of
seafloor spreading
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The Test:
Princeton PostDoc Fred Vine
So, they checked. NOT FALSE
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Structure of
three Plates
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Three boundary types, divergent, convergent, and transform
Also: Oceanic Crust youngest at ridges
Hess model prediction: sea floor youngest at ridges, oldest at edges
Also NOT FALSE
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Oldest ~ 200 my
Plate tectonics: The new paradigm

Earth’s major plates
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Associated with Earth's strong, rigid outer
layer



Known as the lithosphere
Consists of uppermost mantle and overlying
crust
Overlies a weaker region in the mantle called
the asthenosphere. The Asthenosphere is hot
and plastic, and sheds heat via convective
currents.
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Mid-ocean
1_20
Ridge
Origin of new Ocean Floor
At the Mid-Ocean Ridge
• Mantle material is move to
the surface.
• Lithosphere (Crust + Upper
Mantle) bulges into a midocean ridge.
• It cracks, exposing the
mantle to low pressures
• Some of the Mantle minerals
are unstable at atmospheric
pressures
• The unstable minerals melt
forming lavas, and cool into
basalt, the main rock of ocean
lithosphere.
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Mantle circulations are an example of convection,
heat transfer by moving material
This example shows transfer of core heat to the upper mantle and crust
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180º
90º
0º
90º
180º
Mid-Atlantic
Ridge
1_15
45º
45º
NORTH
AMERICAN
PLATE
JUAN DE
FUCA
PLATE
EURASIAN
PLATE
ARABIAN
PLATE
CARIBBEAN
PLATE
PACIFIC
PLATE
PHILIPPINE
PLATE
AFRICAN
PLATE
COCOS
PLATE
0º
PACIFIC
PLATE
FIJI
PLATE
SOUTH
AMERICAN
PLATE
NAZCA
PLATE
SCOTIA
PLATE
45º
0º
Mid-Atlantic
Ridge
INDIANAUSTRALIAN
PLATE
45º
ANTARCTIC PLATE
180º
Convergent plate
boundary
Divergent plate
boundary
Transform plate
boundary
ANTARCTIC PLATE
90º
180º rate
Plates move0ºrelative to each other at90º
a very slow but continuous
Average about 5 centimeters (2 inches) per year
Seven major lithospheric plates
Cooler, denser slabs of oceanic lithosphere descend into the mantle
Seven or so smaller ones.
Plates are in motion and change in shape and size
Largest plate is the Pacific plate
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Several plates include an entire continent plus a large area of seafloor
1_22a
Concept caused revelation. Yes, revelation. Earth’s many features were
all caused by the same process.
Oceanic lithosphere
being subducted
(a)
Water driven out of
ocean lithosphere
Water hits mantle,
which partially melts.
Forms a deep basaltic
magma
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Plate boundaries
Each plate bounded by combination of all three
boundary types: divergent, convergent, transform
Edges marked by Earthquakes
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Three main plate boundaries
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Okay, lets go back over this in more detail.
We saw divergent plate boundaries

Most divergent plate boundaries are located
along the crests of oceanic ridges
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Mid ocean ridges are the site of seafloor
spreading
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Seafloor is elevated by asthenosphere
upwelling and expansion due to heating,
forming oceanic ridges
How people learn, teaching method
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1_20
Mid-ocean
ridge
The upwelling at the mid-ocean
ridges occurs where rising
convection currents in the
mantle reach the lithosphere
and diverge.
Sea-level is raised.
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Divergent boundaries are located
mainly along oceanic ridges
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Divergent boundaries in Continents

Continental rifts “RIFT VALLEY”
 Splits landmasses into two or more smaller
segments
 We are above the rift that opened the
Atlantic about 190 mya. Began 200 mya.
We sit above the western continental
half. Identical rocks (red shales, basalts
from lava flows, lake deposits) can be seen in
Morocco.

Modern examples include East African rifts
Produced by extensional forces acting on the lithospheric plates

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The East African Rift
The rift valley
collects river and
lake sediments.
Land animals
are preserved as
fossils instead of
being eroded
away
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Continental Rift into Ocean Basin
Rift Valleys
and Oceans
are the
same thing
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Convergent plate boundaries
•On the other side of a plate, opposite the diverging
margin, a converging margin is common.
•Three different types, formed from pushing
together of ocean floors and/or continental plate
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Types of Convergent Boundaries
Ocean-Continent
Descending convective
cell this side
Yields Continental
Volcanic Arc
Ocean-Ocean
Yields Volcanic Island
Arc
Descending convective
cell this side
Continent-Continent
Yields Collision Mtns.
Alps, Himalayas,
Appalachians
Descending convective51
cell this side
1_22a
1. Ocean - continent convergence
A volcano forms as magma
reaches the surface
Oceanic lithosphere
being subducted
(a)
A Subduction Zone
As plate descends into the Subduction Zone, partial melting of mantle rock makes magmas
(Molten Rock) These are buoyant, and rise.
Volcanic mountains associated with subduction are called volcanic arcs.
Andes and Cascades mountains are continental volcanic arcs
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Types of convergent boundaries:
2. Oceanic-oceanic convergence
When two oceanic slabs converge, one descends
beneath the other.
Often forms volcanoes on the ocean floor above the
subduction zone.
If the volcanoes emerge as islands, a volcanic island
arc is formed (Japan, Aleutian islands, Tonga islands)
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3. Continental-continental convergence
1_22b
• Continued subduction brings continents together
• Less dense, buoyant, thick continental lithosphere does not subduct well
•Result is a collision between two continental blocks. Process produces folded
mountains (Himalayas, Alps, Appalachians)
Collisional
mountains
Fault and Fold Mountains
(b)
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Rocks deformed in collision
The collision of India and Asia
produced the Himalayas
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Transform fault boundaries
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
Third type of plate boundary
Plates slide past one another and no new lithosphere is
created or destroyed
Transform faults

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Most join two segments of a mid-ocean ridge
(MOR) as parts of linear breaks in the oceanic
crust known as fracture zones
Accommodate simultaneous movement of offset
ridges
Source of weak (MOR) to fairly strong (San
Andreas) earthquakes.
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Transform faults accommodate
movement on offset ridge segments
Plates are moving in
opposite directions
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Plate Tectonics Explains It All


We now understand mountains, volcanoes, and
big earthquakes associated with, for example,
the San Andres fault.
We understand rift valleys and how oceans form,
deep ocean trenches, mid-ocean ridges, why
fossils and mountain ranges look alike across
vast oceans.
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Dirk Egbert Vogel