Transcript Document

Geologic Time
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Mr. Litaker
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Introduction
There has been much debate about Earth’s age and many
scientists have come up with their own theories including:
Greek- Xenophanes … b/c of fossils Earth was old

Greek- Herodotus… counted deposition at the Nile
River

1779 Count de Buffon … compared Earth to a ball of
cooling iron and came up with 75,000 yrs.

1889 John Joly… Used the salinity of Ocean water by
measuring the amt. of salt entering the ocean & concluded
that the Earth was 90 million yrs. old.

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James Hall
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William Thompson (a.k.a. Lord Kelvin)
Measured the rate of heat flow out of
Earth’s surface and said Earth had to be
20 to 40 million yrs. old.
Lord Kelvin is widely
known for developing the
basis of Absolute Zero, and
for this reason a unit of
temperature measure is
named after him.
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At the University of Glasgow he
did important work in the
mathematical analysis of electricity
and formulation of the first and
second Laws of Thermodynamics
ERNEST RUTHERFORD
 **
Finally,
 ERNEST RUTHERFORD
began to study Radioactivity as a
means of determining the age of
the Earth.
 This method has become the
CHIEF CORNERSTONE as to
August 1871–19 October 1937)
the age of the earth!!!
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ERNEST RUTHERFORD
 was
a New Zealand chemist and physicist who
became known as the father of nuclear physics.[1]
He discovered the concept of radioactive half life,
proved that radioactivity involved the
transmutation of one chemical element to another,
and also differentiated and named alpha and beta
radiation. He was awarded the Nobel Prize in
Chemistry in 1908 "for his investigations into the
disintegration of the elements, and the chemistry of
radioactive substances".
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Major John Wesley Powell
1869  Major John Wesley Powell
led an expedition down the Colorado
River and through the Grand
Canyon. Powell realized that the
ROCKS held the Key as to the age
of the Earth.
 Rocks – record geologic events and
changing life forms of the past.
Erosion has removed some of the
record but a lot still remains.

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 Today,
the Geologic Time Scale has
revolutionized the way people look at the age of
the Earth.

the mid-1600’s, Archbishop James Ussher made
a time line of both human and Earth history &
determined the Earth was created in 4004 B.C. 
Book – widely regarded as sacred truth among
religious leaders (even today).
 In

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Uniformitarianism  Late 1700’s, James Hutton
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published his Theory of
the Earth. Hutton put forth
the idea of
UNIFORMITARIANISM—
means that the forces we
observe today have been
at work for a very long
time. < Comparing the
past to our present> Ex:
Meteorite (No witness but
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evidence is there)
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James Hutton
Hutton's Unconformity is any of
various famous geological sites in
Scotland. These are places
identified by 18th-century Scottish
geologist James Hutton as an
unconformity, which provided
evidence for his Plutonist theories
of
Uniformitarianism
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Unconformity – A Gap in the Rock Record

An unconformity is a buried erosion surface separating
two rock masses or strata of different ages, indicating that
sediment deposition was not continuous. In general, the
older layer was exposed to erosion for an interval of time
before deposition of the younger, but the term is used to
describe any break in the sedimentary geologic record.
 Three
Types
 Disconformity
 Angular
Unconformity
 Nonconformity
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Disconformity
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Disconformity is an unconformity
between parallel layers of sedimentary
rocks which represents a period of erosion
or non-deposition.
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Angular Unconformity
 Angular
unconformity
 Angular unconformity
 Angular unconformity is an unconformity where
horizontally parallel strata of sedimentary rock are
deposited on tilted and eroded layers, producing an
angular discordance with the overlying horizontal
layers.
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Angular unconformity
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This is a good example of an
"angular unconformity" in which
tilted sedimentary beds are overlain
by horizontal beds.
This unconformity represents a long
gap in the record of geological time,
during which deposition had ceased
and folding or faulting occured, the
lower strata tilted, and then
deposition resumed.
Hutton Unconformity at
en:Jedburgh, en:Scotland,
illustrated by en:John Clerk in 1787
with a recent photography (2003)
by Keith Montgomery.
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Hutton's Unconformity at Siccar Point
Siccar Point red capstone closeup.jpg
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Non Conformity
A nonconformity exists between sedimentary rocks and
metamorphic or igneous rocks when the sedimentary rock lies
above and was deposited on the pre-existing and eroded
metamorphic or igneous rock. Namely, if the rock below the
break is igneous or has lost its bedding by metamorphism, the
plane of juncture is a nonconformity.[3]
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Relative Dating
Relative Dating—tells us the sequence in which events
occurred, NOT how long they occurred. What came 1st,
2nd, 3rd…

Law of Superposition
 Nicolaus Steno, a Danish anatomist from 1636-1686, is
credited with the Law of Superposition—states that in an
undeformed sequence of sedimentary rocks, each bed is
older than the one above it and younger than the one
below it. EX: Grand Canyon


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
Principle of Cross-Cutting Relationships

Steno’s 3rd observation – states that when a fault cuts
through, or magma intrudes a layer of rock, the fault or
intrusion is younger
 than the rocks affected.


Rock Layers—must have been there 1st in order to
provide rock fragments, so intrusions are younger than
the layer they intrude.
 (T)

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In 2 horizontal layers.
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The
Geologic
Time
Scale
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The Paleontology Portal
a gateway to North American paleontology resources
Understanding Evolution
your one-stop source for information on evolution
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