1. Geologic Time 12
Mr. Litaker
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2. 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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3. 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.
** 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!!!
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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4. 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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6. 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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11.  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 , 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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15. 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.
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35. In 2 horizontal layers.
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36. The Geologic Time Scale
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37. On-Line Sites for Supplemental Learning
The 2 below work great for Earth and Biology:
The Paleontology Portal a gateway to North American paleontology resources
Understanding Evolution your one-stop source for information on evolution
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The history of ideas, research, and contributors in the study of evolution