Interpreting Geologic History Outline

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  • 1. Name _________________________________ Earth Science Interpreting Geologic History #1 Relative Age THE PRINCIPLE OF UNIFORMITY: Geologists can infer events of the past by ____________________________ ___________________________________________________________ Uniformitarianism (Principle of _____________________________) states that the forces that acted upon the ______________________ crust in the__________________ are the same as those that are ________________________ today. ****_______________________________________________________________**** Relative Dating Techniques: Five Basic Laws! 1. Law of _______________________________________________ 2. Law of _______________________________________________ 3. Law of _______________________________________________ 4. Law of _______________________________________________ 5. Law of _______________________________________________ 1. Law of Original Horizontality: _________________________________________________________________ _____________________________________________________________ If strata are _______________ then they must have suffered some kine of disturbance after they were deposited. 2. Law of Superposition- the principle that the _______________ layers in a sequence of rock strata must have been deposited _________________ the layers above, unless the rock strata have been ___________ or _____________. The __________rocks are found at the bottom. Geologists can date the ____________ ages of the strata from __________ to ___________ .
  • 2. 3. Law of Inclusions: A rock must first exist in order to be weathered, deposited and cemented as a ___________ in another rock. Therefore, If rock is composed of _________, the rock fragments must be _____________ than the rock in which they are found. _______ is older in A. _____________ is older in B. The law of inclusions also applies to fossil preserved in bedrock. _____________________ are any naturally preserved remains or impressions of living things. They are found in ___________________________________, because _________________________________________________________________ ______________________________________________________________ Fossils give us information about __________________________________________________. 4. Law of Cross-Cutting Relationships: Any ___________ or ____________ must be younger than ALL the rock through which it cuts. Simply put, the body of rock that is cross-cut had to be there first in order to be cut by an intruding igneous body or fault. In general rock is always ____________________ than the process that changed it. Some processes include: ________________, ______________, _________________, __________________ & ________________. These changes can lead to exceptions to the Law of Superposition:
  • 3. a. __________________________ is an igneous rock that formed from lava on the surface of the crust. An _____________________ must be younger than the strata below it, but _________________ than any layers above. b. _____________________ are created when molten rock ( ____________) is injected into older rock layers in the crust. ___________ are ____________ than all the rock layers in contact with them. c. ___________________ are bends in rock strata. _____________________ can overturn rock strata so that ______________ rock lies on top of _____________rock. d. _________________ are cracks in rock strata. _______________ produce offset layers. Processes that can change the order of rock strata: Rock strata must be _________________ than the process that changed it. _________________, _______________ and __________________ __________________ are features created after rock or sediment has been deposited. 5. Law of Original Lateral Continuity: When sediment is dumped by an agent of erosion, strata extends from the source of deposition until it gradually thins to zero, or until it reaches the edges of the basin of ____________________. This concept enables geologists to correlate outcrops of strata that has been dissected by processes of ______________. CORRELATION OF ROCK STRATA: A. Correlation is ______________________________________________________________ ___________________________________________________________ ______________________________________________________________
  • 4. B. Ways to correlate rock formations: 1. “Walking the outcrop” is done by ______________________________________________ This is correlation by _____________________________________. 2. You can match the rock strata in one location with the rock strata in more distant locations by ____________________________________________________________ _______________ 3. Time correlation compares ______________ ________________ contained in rock the strata. 4. The best index fossils: a. ______________________________________________________ b. ______________________________________________________ 5. Another way of correlating layers by time is through ________________________________. These ash falls are very __________________ events. A single layer of _________________ can be found over a large area, this allows geologists to make a ________________________ from one location to another at the position of a common ash fall. GEOLOGIC TIME SCALE: Geologists noticed that rock __________________________ could be identified by the fossils they contained. They also found that certain _____________________ were consistently located _____________________ or ______________________ other formations. From these observations they established a ___________________ ____________ ___________ With a sequence of fossil groups from _____________ to ______________each of these groups was named for a location where its __________________________ could be observed in the rocks. Example:___________________________
  • 5. Further observations from around the world established a _________________ ________________ __________________ based on _______________________________________________ AND _________________________ex:________________&______________ An _________________________ is the process of mountain building. SEE PAGES 8 & 9 IN YOUR ESRT!!! GEOLOGIC EVENTS OF THE PAST: A. _________________________ causes gaps in the geologic record. B. When a new layer of rock is laid down on a surface that has been __________________________, it forms a buried erosion surface called an _________________________________________. C. How an unconformity forms:
  • 6. Name _________________________________ Earth Science Interpreting Geologic History #2 Absolute Age RADIOACTIVE DATING: Fossils enabled geologists to give __________________________ time, Measurements of natural _________________________ in rocks have allowed _________________ time scale to be an __________________ time scale. The ________________ _______________ of an object is measured in years. Chemical elements often have several forms called _________________________. ISOTOPE: ______________________________________________________________ ______________________________________________________________ Ex. C C If the nucleus has more or fewer than the normal number of ___________________, The isotope may be _______________________________. Radioactive isotope will break down naturally into a lighter element called _____________________ _______________________. Carbon –14 → C-14 Potassium-40 K40 → → Uranium-238 U238 → Rubidium-87 Rb87 → Example: see front cover of reference table The rate of decay of a radioactive element is measured by it’s ___________ _________
  • 7. HALF-LIFE: _____________________________________________________________________ Complete the Chart using your Reference Table: RADIOACTIVE ELEMENT DECAY PRODUCT HALF-LIFE 1 Carbon-14 2 Potassium-40 3 Uranium-238 4 Rubidium-87 Calculating the age of a rock: 1. What would be the age of the rock that has equal amounts of C-14 and its decay product N-14? 2. What % of the sample is radioactive after the following half-lives, After 1 half-life: After 2 half-lives: After 3 half-lives: 3. After 11,200 years how much C-14 would remain in a 10 gram sample? Selecting the Best Radioactive Element: AGE OF SAMPLE RADIOACTIVE ELEMENT 1 Under 50,000 (RECENT) 2 Over 50,000 (OLDER)
  • 8. * Carbon-14 is used for dating: _____________________________________________ & _____________________________________________