Arthur

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Arthurs Seat, Edinburgh, Scotland Debbie Amato
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Geology and the Methods of Science
Basic Assumption The Earth works in an orderly
fashion in which natural phenomenon will recur
given the same set of conditions.
1. Question We want to know how some part of
the Earth works.
2. Data Collection Observe, measure, describe,
compile.
3. Hypothesis! A logical but tentative
explanation that fits all the data collected and
is expected to account for future observations as
well.
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4. Testing. Testing, testing, and more
testing. 5. Modification. Hypotheses are
modified to include the results of testing (see
4). 6. Theory! The hypothesis now withstands
rigor of all the testing (see 4) and
consistently explains accumulating data to
become a THEORY. A theory is a generally
accepted explanation for a given set of data or
observations. 7. Testing. The theory is
tested, tested and tested again. 8. Scientific
Law! If a theory meets rigorous testing over a
long period of time it may become a SCIENTIFIC
LAW. 9. Principle. Generally a scientific law
so fundamental to geology that it provides the
foundation of the science.
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GEOLOGICAL CONCEPTS 1. Catastrophism -
Observations led to the belief that the
Earth developed through a series of upheavals
that were relatively short-lived. A hypothesis
that was proven inadequate and discarded.
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Through Geology, we have learned that the Earth
is very old (4.6 billion years). So. Time,
time, time is on my side, yes it is.
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Siccar Point, Scotland
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2. Principle of Uniformitarianism - James Hutton
discovered that Earth processes acted over a
long period of time (1830s). Hutton proposed
that the physical, chemical and biological
processes observed on a daily basis, have also
acted on the Earth over very long periods of
time. Observations of current geological
processes could be used to interpret the rock
record of very old geologic events.
BIRTH OF MODERN GEOLOGY
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Other Important Geologic Principles Superposition
- The scientific law stating that in any
unaltered sequence of rock strata, each stratum
is younger than the one beneath it and older than
the one above it, so that the youngest stratum
will be at the top of the sequence and the oldest
at the bottom.
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Principle of Original Horizontality - The
scientific law stating that sediments settling
out of a fluid (air and water) are deposited
horizontally or nearly horizontally in layers
that lie parallel or nearly parallel to the
Earths surface.
Photo by Kevin Hefferan Badlands National Park
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Principle of Cross-Cutting Relationships - The
scientific law that states an igneous intrusion
or geologic structure is always younger than the
rock that surrounds it.
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Siccar Point, Scotland
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Siccar Point, Scotland
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Principle of Inclusions - The scientific law
stating that rock fragments contained within a
larger body of rock are always older than the
surrounding body of rock.
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So Where do we begin our study of
The Earth ?
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The Creation of the Solar System
Begin with the Big Bang approximately 12
billion years ago. Space expanded rapidly and
then began to contract. As temperatures cooled,
Hydrogen and Helium gases formed. Denser pockets
of gas condensed further due to gravity.
Accumulations became galaxies. Began to rotate to
form disc-shaped clouds. Center collapsed to form
the Sun. As heat increased in the Sun, particles
were blown away as solar wind. Particles
collided and accreted becoming planetesimals.
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So how did we get to here?
As larger and larger particles collided, larger
planetesimals were formed. Some of these
continued to collide and the largest became the
planets, while the smaller ones may have become
moons.
Intense solar radiation heated the closest
planets causing the lighter elements to be
vaporized and blown out into space. This
concentrated the heavier elements like iron and
nickel on the inner planets and the lighter
elements on the outer planets.
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The Earths Earliest History
Beginning of the Earth was extremely
violent. Grew by planetesimal impact. Became very
hot, heated to the melting point of
iron. Innermost rocks began to become compressed,
so more heat. Radiogenic heat was added due to
radioactive fission. Earth underwent
differentiation into layers.
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Early Differentiation of the Earth
What was the Earths early composition? Need to
consider meteorites that have struck the earth to
get an idea of composition. Most are iron and
nickel. Some contain chondrules. Small rocky
bodies within the meteorites that may represent
matter condensing from the original solar
nebula. Earths composition should be similar
to these meteorites. However - Meteorites are 35
iron, while Earths surface rocks only 6 .
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Early Differentiation of the Earth
Where did the iron go? As Earth was still
accreting, temperature rose above melting point
of iron. Iron liquified. Because of higher
density, iron sank into the proto-Earths center
due to gravity. Lighter elements rose to the
surface. Originally, Earth was homogeneous. Due
to heat and melting, Earth materials separated
forming concentric zones of differing
density. Thus, Differentiation.
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Differentiation and the Earths Interior
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Earths Interior
Three Principal Layers Each has different
Composition and density (mass/volume). CRU
ST - Outermost layer Density low
Composition is silicon and oxygen-based minerals
and rocks. Crust is extremely
thin. Consistency is rocky.
Composed of two general types. Continental
crust Oceanic crust
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Earths Interior
Three Principal Layers Each has different
Composition and density (mass/volume). CRU
ST - Outermost layer Density low
Composition is silicon and oxygen-based minerals
and rocks. Crust is extremely
thin. Consistency is rocky.
Composed of two general types. Continental
crust Oceanic crust
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Earths Interior
MANTLE - Middle thin layer Density
medium Composition is silicon and
oxygen-based but also includes iron
and magnesium. Consistency is plastic.
Contains two parts, Upper and Lower Mantle. CORE
- Inner layer Density high
Composition is primarily iron and nickel.
Contains two parts Inner core is solid. Outer
core is liquid.
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Subdivisions of the Earths Interior
Within these three principal layers are
subdivisions.
Crust consists of OCEANIC CRUST
(brown) CONTINENTAL CRUST (green). Oceanic
crust is thin (8-10 km), dense, and found
below ocean basins (blue). Continental crust is
thicker (20-70 km), has low density and forms the
bulk of continents. The crust rides on the very
upper most portion of the mantle.
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The outermost sublayer is the most active
geologically. Large scale geological processes
occur, including earthquakes, volcanoes, mountain
building and the creation of ocean
basins. Contains parts of the upper mantle and
all of the crust. Called the LITHOSPHERE (rock
layer).
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Lithosphere is a strong layer, but
brittle. Represents the outer approximately 100
km of the Earth. Thicker where continents exist,
thinner under oceans. Below the lithosphere
resides the ASTHENOSPHERE (weak layer).
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Asthenosphere is part of the upper
mantle. Asthenosphere is heat softened and acts
like a plastic. It is weak, slow flowing, yet
solid rock. (Things that make you go,
hmmm.) Generally 100 to 350 km beneath Earths
surface.
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Overlying the lithosphere is the
ATMOSPHERE. Composed of gases released during
volcanic eruptions and from plant respiration.
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Outgassing from volcanoes also helped produce the
water in the Earths ocean basins. Led to the
initial development of the HYDROSPHERE. Together,
the Lithosphere, Atmosphere and
Hydrosphere support the BIOSPHERE.
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Earliest atmosphere was comprised of H, He,
ammonia (NH4) and methane (CH4). Combination was
deadly to life as we know it. Modern atmosphere
is composed of
Nitrogen (N) 79 Oxygen (O) 20 Argon
(Ar) 1 All other gases lt1
Atmosphere protects us from a variety of
dangerous particles.