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Geology 120 - Geologic Time

by: Savannah McNealy

Geology 120 - Geologic Time Geology 120

Marketplace > Colorado State University > Geology > Geology 120 > Geology 120 Geologic Time
Savannah McNealy
Exploring Earth: Physical Geology (GT-SC1)
Sean Bryan

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Geologic Time
Exploring Earth: Physical Geology (GT-SC1)
Sean Bryan
Class Notes
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This page Class Notes was uploaded by Savannah McNealy on Tuesday February 9, 2016. The Class Notes belongs to Geology 120 at Colorado State University taught by Sean Bryan in Spring 2016. Since its upload, it has received 22 views. For similar materials see Exploring Earth: Physical Geology (GT-SC1) in Geology at Colorado State University.


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Date Created: 02/09/16
Geologic Time Tuesday February 9 2016 942 AM Relative dating puts geologic events in chronological order while absolute dating assigns a nun events fossils could be used to correlate rocks ofthe same age William Smith is credited with formulating the specific types different time intervals 0 Created a geological map of England and Wales 39 Had no dates but was aware of concept that young on top of older ones formulated later on by Nicolas Steno 39 almost every period of the Phanerozoic is represented along that section through primitive geological time scale 0 His work set the stage for naming and ordering geologic time periods if the rocks aren39t horizontal something happened to change Information needed to identify the ages of the rocks wasn39t known until the 20th century Geologic time is divided into 4 eons o Hadean o Archean o Proterozoic o Phanerozoic quotvisible lifequot 390 U m m E E E 2 o o o I In C 8 In 00 In Ln ltr m N O Hadean Archean Proterozoic Eras Pe ods J Phanerozoic Paleozoic Mesozoic Carbon Cambrian Ordovician Silurian Devonian iferous Permian Triassic Jurassic Cretaceous Quaternary 540 Ma 488 Ma 444 Ma 416 Ma 359 Ma 299 Ma 251 Ma 202 Ma 146 Ma 65 5 Ma 23 0 Ma 26 Ma Era nerical age to geologic oforganisms lived during sedimentary rock forms Males and England it is a athem Periods Epochs O 655 Ma 558 Ma 339 Ma 230 Ma 53 Ma 2 Pliocene Pleistocene quot39 Holocene any rock fragments that are included in rock must be older than the rc induded any geological feature that cuts across or disrupts a younger than the feature that is disrupted an interruption in the process of deposition of sedimentary rocks represent m Unconformity Type Description Nonconformity A boundary between nonsedimentary rocks below and sediment Angular unconformity A boundary between two sequences of sedimentary rocks where t have been tilted or folded and eroded prior to the deposition oft in Figure 88 o Disconformity A boundary between two sequences of sedimentary rocks where t have been eroded but not tilted prior to the deposition of the you Figure 87 Pa raconformity A time gap in a sequence of sedimentary rocks that does not show unconformity or a disconformity a 5 J r 39 Egg g H 8 Nonsgdimentaw rock H V Tilted and eroded sedimentaryroclt I i l39 39 f 11 j I o c d ssssssssss ck in which they are mother feature must be issing time ary rocks above he underlying ones he younger ones as he underlying ones Jnger ones as in up as an angular Numerical Dating 0 How does radioactive decay occur breakdown of certain isotopes 39 Before decay all the atoms are unstable parent atoms 39 Half Life is when half of parent atoms decay into daughter atoms 39 After a second half life 14 parent atoms remain Isotopic dating methods are applied by dating igneous rocks that cut across sedimentary rocks that lie within sedimentary layers 0 We know the decay rates of some unstable isotopes and they ve been constant over tin 0 We can39t date the sedimentary rocks themselves because you would be defining the grai 0 There are many isotopic pairs that you can be dated 39 Potassiumargon 39 Uraniumlead 39 Rubidiumstrontium 39 Carbonnitrogenradiocarbon Other Dating Methods 0 Tree Ring Dating dendronchronology 39 Can go back to the height of the last glaciation 39 Used to date the last major subduction zone earthquake on the coast of British Col 0 Reversals of Earth39s magnetic field Magnetic Chronology 39 The earth39s magnetic field make compasses point toward the north pole but it didI I Earth39s magnetic field has reversed itself completely a few times 39 Oceanic crust becomes magnetized by the magnetic field that exists as the crust fo 39 Measure it using magnetometer 39 By matching the seafloor magnetic stripes with the known magnetic chronology v at any point on the plate or volcanic ash layers 1e ns of sand within them umbia n39t use to be that way rmsfrom magma ve can determine the age


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