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Geologic Time

Mr. Litaker12

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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.

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.

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

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.

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 the age of the earth!!!

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August 1871–19 October 1937)

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.

  In 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).

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Uniformitarianism Late 1700’s, James Hutton 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 evidence is there)

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James HuttonHutton'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 TypesDisconformity 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.

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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Siccar Point red capstone closeup.jpg

 

Hutton's Unconformity at Siccar Point

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Non ConformityA 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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On-Line Sites for Supplemental Learning

 http://www.ucmp.berkeley.edu/

 The 2 below work great for Earth and Biology:

  

 

The Paleontology Portala gateway to North American paleontology resources

Understanding Evolutionyour one-stop source for information on evolution