GEO 1111 Lecture Notes - Lecture 6: Geologic Time Scale, Radiometric Dating, James Ussher

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14 Aug 2016
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The geological time scale
James Usher said Earth began
The begat statements (said earth is about 6000 yrs old)
Jack Hills; metaconglomerate (AUS), zircons in this rock are over 4 billion
yrs. Old, oldest radiometric dating made
Relative dating + absolute dating = geological time scale
Relative dating
Relative ages for different rocks
Stratigraphy (study of rock layers)
Strata are deposited horizontally
Rockies consist of sedimentary rocks, forces of compression at plate
boundary have tilted these strata
Stratigraphy
Study of large scale patterns in rocks
Principle of superposition: higher rock unit is younger than lower
Lateral continuity: strata tend to extend in all directions
1. Principle of cross-cutting: a layer that cross-cuts another is the younger
of the two
2. Principle of inclusion: structure included in another is the oldest
3. Principle of faunal succession: fossils in stratigraphic succession change
upward in a predictable way
4. Principle of uniformitarianism: the physical laws of nature have remained
the same since the dawn of time
Fossils used to define geological periods are called index fossils (ex:
ammonites), preferably lived for short amount of time in large area
James Hutton: father of geology
Correlation: find similar units in other regions to prove or disprove
1. Lithostratigraphy: involves study of large-scale patterns in the physical
characteristics of strata, lithostratigrahic unit (present in large area)
2. Biostratigrophy
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