Chapter 6- Earth evolution and Earth structure

Question 1

solar system

Answer 1

consists of the sun, planets, moons, comets, and asteroids

Question 2

sun

Answer 2

a star composed of hydrogen and helium, largest object in the solar system, making up 99.8% of the total mass of the solar system

Question 3

Planet

Answer 3

a sizeable objects orbiting a star, massive enough to have it’s own gravity

Question 4

moon

Answer 4

/natural satellite, body that orbits a planet

Question 5

asteroids

Answer 5

rocky objects which failed to form a planet

Question 6

meteorites

Answer 6

rock fragments which fall to earth from space

Question 7

comet

Answer 7

composed of ice and dust. outer layer melts into water vapour as it gets closer to the sun

Question 8

Density/Composition/Comparison of metallic meteorites

Answer 8

7.0-8.0 gcm-3. Iron and nickle with some sulfur and silicon. Similar to Earth’s core

Question 9

Density/Composition/Comparison of stony meteorites

Answer 9

3.0-3.7 gcm-3, silicate minerals similar to peridotite, similar to Earth’s mantle. high porosity

Question 10

Protoplanetary disc

Answer 10

rotating disc of dense gas and dust surrounding a newly formed stars

Question 11

Planetisimals

Answer 11

solid objects in protoplanetary discs

Question 12

protoplanet

Answer 12

moon-sized planetary body that formed within a protoplanetary disc

Question 13

Impact crater

Answer 13

-circular with a rim of broken rock built up of ejected material
-quartz grains may be shocked or even melted
-rock strata are tilted
-material at depth is broken up
-ejected material is in an inverted sequence

Question 14

Elastic rebound theory

Answer 14

-two parts of a solid/brittle/competent rock are under stress from opposing forces
-the body of the rock is deformed and put under strain
-energy applied is stored as elastic strain energy
-deformation continues until the stress is more than the strength of the rock and it snaps
-the two parts of the rock suddenly move relative to each other and there is displacement along the fault
-elastic strain energy that was stored is transmitted through the earth by seismic waves

Question 15

stress

Answer 15

the force per unit area acting on/within a body

Question 16

strain

Answer 16

the change in shape of a body in response to stress

Question 17

seismometer

Answer 17

a device which receives seismic vibrations and converts them into a signal which can be transmitted and recorded

Question 18

seismogram

Answer 18

paper or electronic record made by a seismograph

Question 19

seismograph

Answer 19

a device which receives and records seismic vibrations

Question 20

P wave properties

Answer 20

-primary, travel fastest and arrive first
-push, longitudinal/compressional waves, can travel through any type of material
-pressure, particles move together and apart (compression and rarefaction) longitudinal

Question 21

S waves

Answer 21

-secondary, travel at 60% the speed of P waves
-Shear, the particle movement is sideways in a shearing motion, making it transverse (cannot travel through liquid)
-several, times larger in amplitude than P waves

Question 22

L waves

Answer 22

-particles oscillate in a circular movement so the wave looses energy quickly with long distance
-travel on the surface
-low frequency, long duration, and large amplitude make them the most destructive
-long, longest wavelength of all the waves
-last, travels slower than P and S waves and arrives last

Question 23

Formula for velocity of a P wave

Answer 23

Velocity = square root of ( (incompressibility + 3/4 rigidity) / (density) )

Question 24

formula for velocity of an S wave

Answer 24

Velocity = Square root of ( rigidity/density )

Question 25

focus

Answer 25

origin of the earthquake

Question 26

epicentre

Answer 26

point on the earth's surface directly above the focus

Question 27

shadow zone

Answer 27

an area where earthquake waves are not recorded (103-142 from epicentre on either side)

Question 28

intensity

Answer 28

measure of surface damage caused by an earthquake

Question 29

mercalli scale

Answer 29

measures the intensity of an earthquale based on the effects felt in the area

Question 30

magnitude

Answer 30

measure of the amount of strain energy released by an earthquake

Question 31

richter scale

Answer 31

logarithmic scale that measures magnitude of an earthquake

Question 32

moment magnitude scale

Answer 32

measures magnitude and leverage on two sides of the fault in an earthquale

Question 33

partial melting

Answer 33

occurs when a small proportion (1-5%) of a rock melts, surrounding the solid crystals reduces the rigidity of the rock, enabling it to behave as rheid

Question 34

lithosphere

Answer 34

rigid layer of the crust and upper mantle

Question 35

rheid

Answer 35

non-molten solid that deforms by viscous or plastic flow

Question 36

low velocity zone

Answer 36

characterized by low seismic velocities, below 100km

Question 37

asthenosphere

Answer 37

layer of the mantle below the lithosphere

Question 38

lithophile

Answer 38

aluminium, calcium, potassium, magnesium, sodium, chlorine, oxygen, silicon very reactive, combine readily with oxygen to form oxides (commonly)

Question 39

siderophile

Answer 39

cobalt, gold, iron, nickle high density transition metls, combine with iron easily, found deeper in the crust so less common on the surface

Question 40

chalcophile

Answer 40

silver, copper, mercury, lead, sulfur, tin, zinc combine with sulfur to form high density sulfides crustal abundance is increased by secondary enrichment

Question 41

atmosphiles

Answer 41

nitrogen, noble gases, hydrogen, carbon liquids/gases found at/above the surface

Question 42

Kimberlites

Answer 42

fine crystal size, ultramafic igneous rocks

Question 43

ophiolite suite

Answer 43

section of oceanic crust and upper mantle broken off and attached to the edge of a continent during plate movement

Question 44

peridotite

Answer 44

an ultramafic igneous rock composed of olivine and pyroxene

Question 45

Direct evidence of the composition of the earth

Answer 45

-Crust beneath our feet -mines and boreholes -volcanoes bringing magma up from depth -ophiolite suites -deep boreholes-

Question 46

Cases studies for superdeep boreholes

Answer 46

-Project Mohole, an attept to reach the moho layer, failed due to increasing costs -Kola superdeep borehole, aimed for 15km, reached 12,200 m at which point the temperature was higher than expected (300'C) and the rock was too plastic for the drillbit to be effective

Question 47

Indirect evidence of the structure of the earth

Answer 47

Density Gravity surveys (gravity anomalies and isostasy)

Question 48

isostasy

Answer 48

theoretical state of equilibrium between the Earth's lithosphere and asthenosphere such that the litho 'floats' at an elevation that depends on its thickness and density. The less dense continents rise to a higher elevation than the denser ocean floors, although the pressure exerted on the asthenosphere is the same

Question 49

Isostatic rebound

Answer 49

rising up on land masses that were once depressed by ice sheets

Question 50

subduction

Answer 50

process where one section of the lithosphere is forced down beneath another

Question 51

slab pull

Answer 51

process where cold dense section of lithosphere sinks into the mantle

Question 52

hot spot

Answer 52

area of high heat flow over a mantle plume

Question 53

thermal flux

Answer 53

measures in watts/square meter or milliwatts/square metre rate of heat energy transfer

Question 54

advection

Answer 54

thermal energy is transferred through a medium by a fluid important close to mid ocean ridges where sea water is drawn down into the crust and replaces rising hydrothermal fluids

Question 55

convection

Answer 55

thermal energy is transferred by a substance (fluid/rheid) due to buoyancy differences within the substance hot material expands, density reduces, and material rises whilst colder denser material sinks under the influence of gravity important in the mantle, atmosphere and ocean more efficient than conduction or advection

Question 56

conduction

Answer 56

thermal energy is transferred through a substance with no overall movement of the substance energy is transferred from atom to atom down the thermal gradient slower than advection or convection

Question 57

why is the interior of the earth hot

Answer 57

heat and formation of the earth radioactive decay

Question 58

electromagnetic surveys

Answer 58

an alternating current is passed through a primary transmitting coil, a magnetic field is induced and spreads into the ground inducing a secondary current in any underground material that can act as a conductor the current sets up an alternating secondary magnetic field, which is detected by the secondary receiving coil

Question 59

seismic tomography

Answer 59

builds up a 3d model by analysing the behaviour of seismic waves as they pass through sections of a body

Question 60

continental roots

Answer 60

tomography models of continents show that at depth under mountain ranges the seismic velocity is higher than expected. supports the theory of isostasy suggesting mountains have cold roots which extent into the mantle

Question 61

curie point

Answer 61

temperature above which magnetic materials loose their permanent magnetism. around 500'C

Question 62

remanent magnetism

Answer 62

recorded in rocks due to their alignment of magnetic minerals according to the earths magnetic field at the time of their formation

Question 63

palaeomagnetism

Answer 63

ancient magnetism preserved in rocks

Question 64

magnetometer

Answer 64

an instrument which detects the strength and direction of the magnetic field

Question 65

magnetic inclination

Answer 65

angle of dip of the lines of a magnetic field

Question 66

origin of the earths magnetic field

Answer 66

the temperatures of the core are above the curie point so can't be a permanent magnet temperature difference between the inner core (5700) and the outer core (3500) induces convection currents in the liquid outer core. the move mass of molten iron generates electricity which induces magnetism, generating more electricity and so on balance between generation and destruction allows the earth to maintain a continuous magnetic field