EESA06H3 Lecture Notes - Lecture 8: North American Plate, Economic Union, Nappe
Geologic Time: How Do We Date the Past?
● Rocks give us absolute ages
● For the most part based on rock layers we focused on relative age dating
Terms to remember
● Strata → layers of rock
● Stratigraphy → sub discipline concerned of age of rocks
● Relative age vs absolute age
● Accomodation → in order to get rocks preserved we need areas of crust that is subsiding
○ Accumulate sediment
○ Opposite of subsidence is uplift → results in sediment erosion
● Conformable succession
○ Continuous records of earth’s surface with nothing breaking
● Unconformable succession
○ Major time breaks in a succession
○ More gaps than record ( more time unrecorded by records; incomplete)
● Index fossils and faunal succession
○ Can age fossils
○ Succession of fossil types through evolution in time
○ Some organisms are long lived
● Brittle failure of rocks to form flauts
○ When rocks break they cause earthquakes
● Plastic deformation of rocks to form folds
● Dip and strike
● Isotope dating using unstable radioactive isotopes
● Parent isotope
● Half life
○ Amount of time it takes half of parent isotope to turn into lead
● The geologic timescale
○ The book with all the chapters identified
○ As much as we know about earth’s history
○ Always updated
● Layers on top are sitting unconformably
● Older stuff isn't flat → rock layers are dipping (tilted)
● Then have been intruded
○ Plutones intruded the other rocks as molten magma
● Disconformities →
a mini unconformity
● Volcanic ash is high resolution area to date
Document Summary
For the most part based on rock layers we focused on relative age dating. Stratigraphy sub discipline concerned of age of rocks. Accomodation in order to get rocks preserved we need areas of crust that is subsiding. Opposite of subsidence is uplift results in sediment erosion. Continuous records of earth"s surface with nothing breaking. More gaps than record ( more time unrecorded by records; incomplete) Succession of fossil types through evolution in time. Brittle failure of rocks to form flauts. Plastic deformation of rocks to form folds. Amount of time it takes half of parent isotope to turn into lead. The book with all the chapters identified. As much as we know about earth"s history. Older stuff isn"t flat rock layers are dipping (tilted) Plutones intruded the other rocks as molten magma. Volcanic ash is high resolution area to date. Very good index fossils fossil useful for dating and correlating strata in which it is found.
