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Introduction to Physical Geology lecture notes Monday 12th week 3

by: Henderson Notetaker

Introduction to Physical Geology lecture notes Monday 12th week 3 GEO 101N - 02

Marketplace > University of Montana > GEO 101N - 02 > Introduction to Physical Geology lecture notes Monday 12th week 3
Henderson Notetaker
GPA 3.34

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these notes are from Monday the 12th of September going over magnetic fields. they are a combination of notes from lecture, slides, and the book. Wednesday and Friday notes for week 3 should be up ...
Intro to Physical Geology
James W. Sears (P)
Class Notes
Geology, magnetic field
25 ?




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This 4 page Class Notes was uploaded by Henderson Notetaker on Friday September 16, 2016. The Class Notes belongs to GEO 101N - 02 at University of Montana taught by James W. Sears (P) in Fall 2016. Since its upload, it has received 4 views.


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Date Created: 09/16/16
Introduction to Physical Geology (GEO 101N­02) Professor: Dr. Jim Sears Elite Notetaker: Cat Henderson Lecture Notes Monday 9/12 ***Disclaimer: the following content is derived from notes I have taken from the required text or from my understanding of the  in class lecture. The notes and/study guides provided are to the best of my ability correct however they are NOT supervised by  the professor nor can I guarantee the absence of all mistakes.  Please understand that the following is my own notes (not my  original findings) from that of the sited material. These notes comply with the University of Montana Academic Dishonesty codes and policies and will not provide answers or cheat sheets for assignments or exams. Thank you for reading and understanding  this. *** Earth’s Magnetic Field Reference: (ch2 slide 13,15­16, pg48 sec2.3 Ess. Of Geo)  Flow in the liquid outer core creates the magnetic field o It is similar to the field produced by a bar magnet o The magnetic pole is tilted ~11.5 degrees from the axis of rotation  Geographic and magnetic poles are not parallel  A compass points to the magnetic N, not the geographic N  declination o The difference between geographic N and magnetic N is called declination. It  depends on: o Absolute position of the two poles  Geographic north  Magnetic north o Longitude o You can see the declination of the magnetic field by looking at rocks. The  magnetic field at the time the rock was formed will show in the rock  Curved field lines cause a magnetic needle to tilt  Inclination o Angle between magnetic field line and surface of the earth is called inclination. It  depends on: o Latitude o Near the poles the magnetic lines become steep whereas at the equator they are  flat. This causes your compass needle to rise or fall vertically Earth’s Magnetic Field Cont.  How Earth’s magnetic field works o Magnetic field of the earth comes from the movement of liquid iron in the outer  core o Earth is hotter on the inside than the outside causing turbulence in the liquid outer core o Rotate iron and it generates an electromagnetic field o As the earth spins it exerts torque on the inner core this orients the flow with the  spin axis of the earth o Spin axis is slightly off of the north pole the magnetic north pole is roughly 11.5  degrees off o Magnetic field is in constant motion o The change of flow in the iron core can flip the magnetic pull switching the  direction of the magnetic fields  Magnetic Poles Reference: (ch2 slide 14, pg48 sec2.3 Ess. Of Geo)  The magnetic pole intersects Earth’s surface just like the geographic pole does o Magnetic N pole and magnetic S pole both exist o Magnetic poles are located near geographic poles o Magnetic poles move constantly Paleomagnetism Reference: (ch2 slide 17­19, pg48 sec2.3 Ess. Of Geo)  Rock magnetism can be measured in the laboratory o Paleomagnetism is more or less fossilized magnetism in rocks  How paleomagnetism works o “paleomagicians” take a rock sample and look at the fossilized magnetic field in  the rock then date the rock and that gives them a rough estimate of the direction of the magnetic fields on earth at that time o Takeing multiple samples from rocks from a certain period can confirm the  direction of the field at that time o This can be used to track continental drift  Iron(Fe) minerals in rock preserve information about the Magnetic Field at the time the  rocks formed o Declination and inclination preserved in rocks often vary o Instruments used in paleomagnetism record changes in position o These data are used to trace continental drift  Iron minerals archive the magnetic signal at formation Paleomagnetism Cont.  Hot magma o High temp – no magnetization  Thermal energy of atoms is very high  Magnetic dipoles are randomly oriented  Cooled magma o Low temp – permanent magnetization  Thermal energy of atoms slows  Dipoles align with earth’s magnetic field  Magnetic dipoles become frozen in alignment with field Polar Wandering Reference: (ch2 slide 20,22, pg50 sec2.3 Ess. Of Geo)  Layered basalts record magnetic changes over time  Inclination and declination indicate change in position  Each continent had a separate polar wandering path. Now understood to represent that: o The location of the magnetic pole is fixed o The continents themselves have moved  These curves align when continents are reassembled Apparent Polar Wandering Reference: (ch2 slide 21, pg50 sec2.3 Ess. Of Geo)  Polar wandering paths were initially misinterpreted o Not the signature of a wandering pole on a fixed continent o The signature of a fixed pole on a wandering continent Sea­Floor Bathymetry Reference: (ch2 slide 23, pg51 sec2.4 Ess. Of Geo)  Before world war II we know little about the sea floor  Echo – sounding (sonar) allowed rapid sea­floor mapping  Sea­floor maps created by ships crossing the oceans  Bathymetric maps are now produced using satellite data The Ocean Floor Reference: (ch2 slide 24, pg51 sec2.4 Ess. Of Geo)  Now using satellites, we have extremely accurate maps of the ocean floor  Oceans are topographically smooth between shelf and ridge as it collects sediment  coming from storms and currents  Continents spread faster in the pacific than the Atlantic The Ocean Floor Cont.  Oceanographers were surprised to discover that: o A mid­ocean mountain range runs through every ocean o Deep­ocean trenches occur near volcanic island chains o Submarine volcanoes poke up from the ocean floor o Huge fracture zones segment the mid­ocean ridge  These observations are all explained by plate tectonics   Sonar mapping delineated bathymetric features o Mid­ocean ridges o Deep­ocean trenches o Volcanic islands o Seamounts o Fracture zones  Today’s satellite view of the ocean floor reveals these bathymetric features


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