TSUNAMI is a very long wavelength, high-speed. ocean wave

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COMMON METAMORPHIC ROCKS
Classified on the presence or absence of
FOLIATION. FOLIATION is the parallel alignment
of tabular minerals in the rock due to heat and
pressure.
Gneiss Foliated
Quartzite Nonfoliated
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COMMON METAMORPHIC ROCKS
Some metamorphic rocks can be produced from a
number of parent rocks, i.e., gneiss. They are
then distinguished by their appearance and the
conditions under which they form rather than by
composition. Others form from specific parent
rocks, i.e., slate.
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COMMON METAMORPHIC ROCKS
METAMORPHIC GRADE describes the severity
of metamorphism. Designated low, medium and high
grade. The higher the metamorphic grade, the
less similar is the metamorphic rock to the
original parent rock.
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Foliated
Nonfoliated
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COMMON METAMORPHIC ROCKS
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USES OF METAMORPHIC ROCKS
Building and foundations Road and railroad
construction (slate and quartzite) Art -
Sculpture (marble) Fire protection
(asbestos) Sinks and counters (soapstone) Powder
(talc) Metal ores (from metamorphism)
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Time is a critical ingredient to most geologic
processes. Geologic time has an immense
vastness. We have 4.6 BILLION years to work
with. (info comes from the moon and
meteorite) To us a decade is a long time! Lots
of events happen in this interval of time. How
big is a billion? Consider 1,000,000,000
seconds. 1,000,000,000 seconds equals 31.71 YEARS!
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Earth processes do occur rapidly. Earthquakes,
landslides, volcanic eruptions, floods and
meteorite impacts. Most take place
slowly. Opening of ocean basins, mountain
building, differentiation of the Earth. This
section will focus on the timing of geologic
events and the ages of Earth materials. This
process is called GEOCHRONOLOGY.
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GEOCHRONOLOGY generally cant be done to
precise instants in time. Dates will typically
have errors applied (/-). Geologists use a
variety of clocks for geochronology. They include
trees, fossils, and radioactive isotopes
to start with.
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GEOLOGIC TIME in PERSPECTIVE
Appearance of first Hominids 3-4,000,000
yBP Demise of the Dinosaurs 65,000,000 yBP First
Land Plants 483,000,000 yBP First
Fish 505,000,000 yBP First Shelled
Invertebrates 570,000,000 yBP First Appearance
of Life 3,770,000,000 yBP Oldest Known Earth
Rocks 3,960,000,000 yBP Age of the
Earth 4,600,000,000 yBP
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GEOLOGIC TIME in PERSPECTIVE
Appearance of first Hominids 4 mm Demise of the
Dinosaurs 65 mm First Land Plants 483
mm First Fish 505 mm First Shelled
Invertebrates 570 mm First Appearance of
Life 3,770 mm Oldest Known Earth Rocks 3,960
mm Age of the Earth 4,600 mm
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GEOLOGIC TIME in PERSPECTIVE
Appearance of first Hominids 3-4,000,000
yBP Demise of the Dinosaurs 65,000,000 yBP First
Land Plants 483,000,000 yBP First
Fish 505,000,000 yBP First Shelled
Invertebrates 570,000,000 yBP First Appearance
of Life 3,770,000,000 yBP Oldest Known Earth
Rocks 3,960,000,000 yBP Age of the
Earth 4,600,000,000 yBP
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GEOLOGIC TIME in PERSPECTIVE
We have the dates of these events carefully
calculated, or so we want you to believe. How
was it done? At first it was done by RELATIVE
DATING. RELATIVE DATING compares two or more
features and/or events to determine relative
age, i.e., which came first, which is youngest.
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GEOLOGIC TIME in PERSPECTIVE
RELATIVE DATING
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GEOLOGIC TIME in PERSPECTIVE
As science and technology advanced we were able
to put actual dates on these features and
events. This process is termed NUMERICAL or
ABSOLUTE DATING. Requires care in
application. ABSOLUTE would indicate that we
know absolutely when events occurred. WE
DONT!!! Numerical dates always represent a range
within a margin of error.
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PRINCIPLES OF RELATIVE DATING
A REVIEW
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PRINCIPLES OF RELATIVE DATING
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.
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PRINCIPLES OF RELATIVE DATING
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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Superposition, cont.
With tilted beds, we need to consider
other sedimentary structures, like ripple
marks, mudcracks, graded bedding,
or cross-bedding to help determine up
direction. Can also use vesicles in lava flows.
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PRINCIPLES OF RELATIVE DATING
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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PRINCIPLES OF RELATIVE DATING
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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PRINCIPLES OF RELATIVE DATING
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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GEOLOGIC TIME in PERSPECTIVE
We have the dates of these events carefully
calculated, or so we want you to believe. How
was it done? At first it was done by RELATIVE
DATING. RELATIVE DATING compares two or more
features and/or events to determine relative
age, i.e., which came first, which is youngest.
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GEOLOGIC TIME in PERSPECTIVE
RELATIVE DATING
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GEOLOGIC TIME in PERSPECTIVE
As science and technology advanced we were able
to put actual dates on these features and
events. This process is termed NUMERICAL or
ABSOLUTE DATING. Requires care in
application. ABSOLUTE would indicate that we
know absolutely when events occurred. WE
DONT!!! Numerical dates always represent a range
within a margin of error.
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PRINCIPLES OF RELATIVE DATING
FOSSILS
FOSSILS are any evidence of past life. Used with
other principles to figure out the order
in which life developed, changed and went
extinct. Very hard to accomplish. Hard to
establish life history for organisms. Only 1 of
all species that ever lived have been preserved
as fossils.
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PRINCIPLES OF RELATIVE DATING
FOSSILS
To be preserved, fossils require special
conditions. Include Rapid burial Hard
parts Most organisms dont have hard parts.
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PRINCIPLES OF RELATIVE DATING
PRINCIPLE OF FAUNAL SUCCESSION
If we know the position of each rock layer in a
sequence, we know their relative age. Then, if
we look a the fossils in the layers, we
can determine the relative ages of them. This
sequence will occur again and again in the
geologic record. Can then be used to provide
relative age of the rocks.
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PRINCIPLES OF RELATIVE DATING
PRINCIPLE OF FAUNAL SUCCESSION
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PRINCIPLES OF RELATIVE DATING
PRINCIPLE OF FAUNAL SUCCESSION
Generally we use INDEX FOSSILS for this
approach. INDEX FOSSILS have short lifespan
(rapid evolution) widespread geographic
distribution and are easy to recognize
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RELATIVE DATING BY WEATHERING RINDS
Relative ages of rocks can be determined by
comparing the extent of weathering preserved in
them. Weathering will produce a RIND of weathered
material at or near the rocks surface. Produced
in a variety of ways.
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RELATIVE DATING BY WEATHERING RINDS
The longer the length of exposure to weathering,
the thicker the rind. Thickness of soil can
also be used in this manner. (Need to use
similar soils produced from similar parent rocks)