origin of earth's structure

Question 1

nebular hypothesis

Answer 1

giant cloud of H and dust collapses, becomes denser (maybe hut by shockwave from exploding star)

size of cloud decreases and r of rotation increases, flattens-protoplanetary disk.
Material drawn to centre by gravity- becomes hot and dense
triggers nuclear fusion increases temp surface of star = visible

accretion of gas into star cont for 10million yrs

p disk cools, smaller grains of rock and ice.
Electostatic and g forces bring grains together- form planetesimals
accrete to form embryotic protoplanets

protoplanets near star collide
form no of small terrestrial planets takes up to 1bn yrs

giant planets - H and He dep onto surface whilst solid materials within disc accretes to form moons

left over planetesimals become asteroids
meteorites- asteroid fragments
comets- planetesimals furthest from sun
(provide info on solar system formation)

our moon prob formed 30-50Ma when protoplanets impacted young earth after ss formation

Question 2

meteorites def

Answer 2

rock from space which reached Earths surface

most come from asteroid belt (form at start of ss)

Question 3

dif between asteroids and meteorites

Answer 3

a- never enter atmosphere

if they do they become meteorites - most burn up before surface

Question 4

chondrules def

Answer 4

found in chondrites- molten droplets (olivine) formed at h temps in early solar cloud (rounded)

Question 5

chondrites

Answer 5

contain chondrules- most abundant meteorite found on earth

85% found on earth

chem sim to sun + whole ss

mostly ultramafic

Question 6

types of meteorites

Answer 6

iron

stony

carbonaceous chondrites

Question 7

iron meteorite

Answer 7

made of Fe and Ni

similar to comp of core
help to understand

Question 8

stony meteorites

Answer 8

mostly si minerals
but still mafic silicic e.g. pyroxene

if contain O and pyroxene then similar comp to mantle
help understand

Question 9

carbonaceous chondrites

Answer 9

organic materials contained in these e.g. Carbon and H20

could be reason for life on Earth

help understand comp of whole earth

Question 10

what causes impact craters

Answer 10

meteorites impact

Question 11

why are there impact craters on moon but not earth

Answer 11

earth has water and veg to cover

earth has the tectonic plates and erosion leading to the cycling of rocks (destroys /fills craters) the moon doesn’t have this

Question 12

evidence of meteor/asteroid impact

Answer 12

circular depression and raised rim

shocked quartz- melted and resolidified or fractured as low mp

inverted strata- top layer hit and projected first so land first,layers flipped

tilted strata- towards centre

rocks at depth may be brecciated- fractured/ broken up

Question 13

larger the impact energy?

Answer 13

the less frequent the occurence

Question 14

Tunguska event

Answer 14

1908 (30/6/08)
in Russia

shook earth to 1000km radius- caused earthquakes + massive shockwaves

trees pointed radially away from ground 0

no crater + trees burned from above - must have burned up before impact

only evidence- found small fragments of lonsdaleite in peat bogs from 1908

crazy theories-
failed Tesla experiment
nuclear explosion from aliens
black hole collided with earth

Question 15

2 main sources of Earth’s heat

Answer 15

Radioactive decay releases energy (mostly in mantle)
- 2/3

heat from formation of the solar system (upon many collision Kinetic e transferred to heat e) - 1/3

Question 16

geothermal gradient def

Answer 16

change in temp with depth as well as rate of change in temp with depth (in earth)

around 25degrees per km for first 50km

Question 17

Heat flow Explanation of heat transferer from source

Answer 17

current thinking

heat transferred from interior to surface- measure via thermal flux (measures rate of transfer) - greater over O crust as thinner so less insulation (100Mw-2to 65 Mw-2)

3 ways of transfer:

conduction- heat transferred atom to atom, no movement of material only vibration

convection-warm materials, expand-less dense-rise-energy transferred by rising then losing e-shrinks- more dense-sinks

advection-transferrer of energy in liquid e.g. at plate boundaries
H2O drawn into lithosphere-heats-rises-carrying heat e

Question 18

conduction

Answer 18

conduction- heat transferred atom to atom, no movement of material only vibration

Question 19

convection

Answer 19

convection-warm materials, expand-less dense-rise-energy transferred by rising then losing e-shrinks- more dense-sinks

Question 20

advection

Answer 20

advection-transferrer of energy in liquid e.g. at plate boundaries
H2O drawn into lithosphere-heats-rises-carrying heat e

Question 21

Convection cells Explanation of heat transferer from source

Answer 21

past thinking

convection in mantle- drives heat transfer

now know Convection and advection is key too

convection cells also don’t drive plate movement- plates move faster

Question 22

changes in geothermal gradient from crust to core

Answer 22

temp increases with depth throughout

rate of temp change changes with depth

greatest in lithosphere

large decrease lithosphere to Upper mantle- (Moho discontinuity)

in U and L mantle r of increase is lower than in lithosphere

increase in geothermal gradient at boundary between lower mantle and outer core (Guttenberg)

similar in outer core and lower mantle

rate of increase lowest in inner core
(lehmann)

Question 23

reasons for changes in geothermal gradient

Answer 23

discontinuities

Moho- rigid to plastic solid and change in comp (more mafic and dense) Crust to upper mantle

Guttenberg-change in state and how heat energy moves through L and S, also change in comp
lower mantle to outer core

lehmann- change in state liquid to solid, not comp
outer sore to inner core

Question 24

Goldschmidt’s classifications

Answer 24

atmophile
chalcophile
lithophile
siderophile

Question 25

atmophile

Answer 25

volatile
affinity to atmosphere

Question 26

chalcophile

Answer 26

ore loving
combines readily with sulphur

Question 27

siderophile

Answer 27

iron loving
affinity for iron
densest sink to depth
so rarest in crust

Question 28

lithophile

Answer 28

found in rocks- oxidise easily

mantle and crust