origin of earth's structure Flashcards
nebular hypothesis
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
meteorites def
rock from space which reached Earths surface
most come from asteroid belt (form at start of ss)
dif between asteroids and meteorites
a- never enter atmosphere
if they do they become meteorites - most burn up before surface
chondrules def
found in chondrites- molten droplets (olivine) formed at h temps in early solar cloud (rounded)
chondrites
contain chondrules- most abundant meteorite found on earth
85% found on earth
chem sim to sun + whole ss
mostly ultramafic
types of meteorites
iron
stony
carbonaceous chondrites
iron meteorite
made of Fe and Ni
similar to comp of core
help to understand
stony meteorites
mostly si minerals
but still mafic silicic e.g. pyroxene
if contain O and pyroxene then similar comp to mantle
help understand
carbonaceous chondrites
organic materials contained in these e.g. Carbon and H20
could be reason for life on Earth
help understand comp of whole earth
what causes impact craters
meteorites impact
why are there impact craters on moon but not earth
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
evidence of meteor/asteroid impact
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
larger the impact energy?
the less frequent the occurence
Tunguska event
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
2 main sources of Earth’s heat
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
geothermal gradient def
change in temp with depth as well as rate of change in temp with depth (in earth)
around 25degrees per km for first 50km
Heat flow Explanation of heat transferer from source
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
conduction
conduction- heat transferred atom to atom, no movement of material only vibration
convection
convection-warm materials, expand-less dense-rise-energy transferred by rising then losing e-shrinks- more dense-sinks
advection
advection-transferrer of energy in liquid e.g. at plate boundaries
H2O drawn into lithosphere-heats-rises-carrying heat e
Convection cells Explanation of heat transferer from source
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
changes in geothermal gradient from crust to core
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)
reasons for changes in geothermal gradient
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
Goldschmidt’s classifications
atmophile
chalcophile
lithophile
siderophile
