Earth magnetic field and paleomagnitism

Question 1

paleomagnitism

Answer 1

description of the geomagnetic field and its spacial(space) and temporal (time) variations

Question 2

magnetic field can be visualized by

Answer 2

lines of force, such as those revealed by alignment of iron filings on a piece of paper above a bar magnet

Question 3

earth’s magnetic lines of force point which direction

Answer 3

into the ground at north magnetic pole and outward at south magnetic pole

Question 4

what kind of magnetic field

Answer 4

dipole (two-pole) magnetic field

Question 5

at the equator, the lines ____ to earths surface
at mid-latitudes, lines ____ to surface
at magnetic poles, lines_____ to the surface

Answer 5

parallel
tilt at angle
perpendicular

Question 6

relative strength of dipole

Answer 6

strength of the field is maximum at either end

at midpoint, the strength is half the value of the poles

Question 7

magnetic field direction of dipole

Answer 7

lines of force leave one end of magnet (north pole) arc through space, and reenter the magnet at the other end (southern pole)

Question 8

difference between magnetic pole and geographic pole

Answer 8

11.5 degrees

Question 9

polar cusps

Answer 9

bend in magnetic field around earth (look at pic on page three)

Question 10

earth’s magnetic field distorted by

Answer 10

solar wind

look at pic on bottom of page 3

Question 11

aurora

Answer 11

caused by polar cusp- charged particles are pulled towards magnetic poles. Interacting with atmospheric gases, these ions create colorful glowing aurora observed in polar regions
In north- called Aurora borealis aka northern lights
in south called aurora australis

Question 12

earth’s magnetic field is not uniform

Answer 12

intensity and direction of the field changes from one location to another but over time as well

Question 13

how much of earth is dipole and nondipole fields

Answer 13

only 90% of magnetic field can be described as dipole

remaining 10% (nondipole) has more complex structure

Question 14

secular (time related) variation

Answer 14

both dipole and nondipole parts of field are changing overtime and this secular (time related) variation is fasted for nondipole part.
Change in field strength occur on time scales of decades and indicate that fluid motions within geodynamo system are in the order of millimeters per second
One of the few “solid earth” phenomena that change significantly over a human lifetime

Question 15

magnetic reversals

Answer 15

spontaneous reversals of magnetic field
reverses its direction at irregular intervals (ranging from tens of thousands to millions of years)
exchanging the north and south magnetic poles, as if magnet flipped 180 degrees

Question 16

another way to create magnetic field

Answer 16

electric currents

Question 17

what part of earth generates magnetic field?

Answer 17

convection in earth’s outer core

Question 18

why scientists believe outer core is responsible for magnetic field

Answer 18

1. made primarily of iron, good electrical conductor
2. convective motions are very rapid in the liquid, low-viscosity outer core. These rapid motions stir up electric currents in conducting iron to create a geodynamo with a strong magnetic field
   Field results from the circulation of liquid iron alloy, an electrical conductor, in earth’s outer core- in other words, behaves like electromagnet

Question 19

dynamo

Answer 19

an engine tha produces electricity by rotating a coil of conducting wire through a magnetic field-
geodynamo in earth’s outer core operate on same principles, except the work comes from convection in outer core

Question 20

is it possible to stir up electric curents in the liquid outer core (and why)

Answer 20

Yes! because:

1. Liquid iron alloy is good conductor
2. convection (buoyancy gradient/temp gradient??)
3. earth’s spin

Question 21

what mineral do you need to study the magnetic field

Answer 21

magnetite aka iron oxide
all pieces of it are magnetic
magnetite from 5mil yrs ago same as magnetic field of earth at that time
always has 2 poles no matter what

Question 22

thermoremanent magnetization

Answer 22

an important property of many very hot, magnetizable materials is that as they cool below about 500 deg C, they become magnetized in same direction as surrounding magnetic field
=lava solidification
look at diagram on top of p 7

Question 23

depositoinal remanent magnetization

Answer 23

chips of mineral magnetite would become aligned in the direction of earth as they fall through the water. this orientation would be incorporated into the rock when the particles become lithified

Question 24

magnetic field reverses itself periodically?

Answer 24

NO! super haphazard

look at chart on top of p 8

Question 25

the seafloor as magnetic tape recorder

Answer 25

in WWII extremely sensitive instruments developed to detect submarines by magnetic fields emanating from their steel hulls
geologists made some slight modifications to these instruments and towed them behind research ships so they could measure local magnetic field created by magnetized rocks beneath the sea
rocks magnetized by earth’s magnetic field in whatever direction field is oriented at the time at which rock is formed
Scientists argued that ocean progressively widens as new seafloor (mafic lava cooling) created along a crack on crest of mid-ocean ridge
As seafloor splits and moves away from ridge, approximately half of newly formed basalt moves to each side, forming two symmetrical bands
Newer material fills crack, continuing the process

Question 26

present direction of magnetic filed aka

opposite orientation of filed aka

Answer 26

normal
reverse
in geologic past, magnetic field switched back and forth erratically between normal and reverse

Question 27

mid ocean ridge

Answer 27

symmetrical of normal/reverse aka positive anomaly (higher magnetic intensity) and negative anomaly (lower mag intensity)
present-day magnetic field is the average
anomaly pattern represents alternating stripes of normal polarity and reversed polarity sea floor

Question 28

magnetism of sea floor

Answer 28

LOOK AT PIC ON PAGE 9

Question 29

isochrones

Answer 29

contours that connect rocks of equal age

Question 30

weird time in magnetic field history

Answer 30

for 40 million years during cretaceous period magnetic field did not reverse- shows how random it is

Question 31

magnetic bands provided evidence in support of theory of

Answer 31

seafloor spreading

Question 32

magnetic bands (stripes) used to determine

Answer 32

ocean floor’s spreading rates

see last slide on page 12

Question 33

magnetic inclination

Answer 33

the needle’s angle of tilt depends on latitude

Question 34

at magnetic north ole, need it is (pointing which direction)

Answer 34

vertical

Question 35

intensity and structure of earth’s magnetic field are changing what sped? How often?

Answer 35

slowly and erratically

Question 36

how often magnetic field strength and direction reevaluated

Answer 36

every 5 years for 5-year period

because a wide range of commercial and military navigation systems are dependent on models of the magnetic field

Question 37

declination

Answer 37

component of magnetic field

indicates the difference, in degrees, between the headings of true north and magnetic north

Question 38

horizontal intensity

Answer 38

component of magnetic field

defines the horizontal component of the total field intensity

Question 39

vertical intensity

Answer 39

defines the vertical component of the total field intensity

Question 40

total intensity

Answer 40

the strength of the magnetic field, not divided into component parts

Question 41

magnetic declination

Answer 41

the angle between magnetic north (direction the north end of a compass needle points) and true geographic north

Question 42

when is declination positive

Answer 42

when magnetic north is each of true north

and is negative when mag north is west of true north

Question 43

magnetic declination varies in what respects

Answer 43

varies from place to place

and with the passage of time

Question 44

isogenic lines

Answer 44

wher the declination has the same value

Question 45

agonic lines

Answer 45

where declination is 0