Chapter 4 - Chapter 4 Introduction Need dates to define...

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Chapter 4 Introduction Need dates to define event in old rocks e Need dates to appreciate time involved in processes - oldest rock is 4.03 billion years old. Earth is 4.54 billin years Note: Archbishop James Ussher: Earth the main event on 26 Oct., 4004 B.C. - Based on careful study of the Bible's continuous record of births and deaths, Ussher was able to place Earth's creation in the year 4004 B.C. That means that Earth is a mere 6000 years old. Relative Dating Principles Nicholas Steno: (1) Principle of Superposition- that sedimentary rock layers are deposited on top of each other. The oldest being at the bottom. Principle of Superposition , also applies to the fossils the rock layers contain, and is consequently at the heart of relative age dating (2) Principle of Original Horizontality - that the layers are flat lying when they are deposited. Steno also argued that sedimentary strata would have lain flat when they were first deposited (Fig. 2); that is, they would have been originally horizontal. (3) Principle of Original Lateral Continuity- that they are deposited over wide areas. the flat lying sedimentary strata would have initially been extended in all directions. hus, steeply inclined rocks must have experienced some later process that deformed them. Using this latter principle, similar strata found on either side of a river valley, for example, must have been originally continuous before the river cut into them. James Hutton Principle of Cross-Cutting Relationships - he was interested in unconformities- those horizons representing a time break during which erosin of a sequence of rocks took place prior to deposition of a more recent dequence. He notes that across the plan of a unconformity, the strata could have dramatically different attitudes. - angular unconformities, which show horizontal layers of  sedimentary rock  lying on  tilted layers of sedimentary rock. The upper layers may not be perfectly horizontal,  but they do not lie  parallel  to the lower layers. The second type of unconformities  are disconformities, which lie between parallel layers of sedimentary rock. The third  type are nonconformities, which divide sedimentary layers from metamorphic and  intrusive (cooled inside the  earth igneous rocks . - Principle of Cross- Cutting Relationships . This principle tells us that a fault is younger than the youngest rock it cuts. That strata above an unconformity are younger than the strata below (J, K and L are younger than A- G); that any feature that cuts across a rock must be younger than the rock it cuts (R must be younger than everything up to and including Q). William Smith
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This note was uploaded on 11/01/2010 for the course EARTH SCIE 2010 taught by Professor Neil during the Fall '10 term at UWO.

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Chapter 4 - Chapter 4 Introduction Need dates to define...

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