midterm Flashcards
geology
evidence collected on every imaginable material to test hypotheses and develop theories on how the earth works
doppler effect and why is it important
the change in wave frequency during the relative motion between a wave source and its observer, important bc it explains red shift
theory vs law
theory: idea supported by lots of evidence
law: precise statement that always applies
star “fingerprint”? why are they significant?
Na, Mg, H, and Ca in stars can block certain wavelenghts of light, so they can be used to make a fingerprint
=> red shift = stationary stars have these bands shifted towards red, using doppler effect shows that distant stars moving farther away (universe ever expanding)
how old is the universe approximately?
15 billion
singularity theory?
everything in the universe used to be in one dot = Singularity, before big bang 13.8 bil years ago
what did the Big Bang form? (right after)
nebula separated by space => [98% H, 2% He, trace Li trace Be, trace B]
why do nebulas collapse and what happens?
particles have gravity so they are pulled towards each other, forms stars and galaxies
why are stars called “elements factory” and what happens when they “run out”
factory => nuclear fusion inside the stars gives us more elements (up until iron, nucleus is too strong can only be fused in a supernova)
runs out => when all the smaller elements (H, He) are used up, the star may collapse into a supernova (1/3 times)
nebular theory?
explains formation of our galaxy
1. nebula left over from supernova
2. nebula collapses & makes a new star
3. orbiting debris flattens into disc
4. planets formed from collisions of smaller debris, clumps form & get bigger n’ bigger (gravity UP)
why are the farther 4 planets gas giants?
volatile elements (evaporate easily) like carbon, nitrogen, hydrogen, and helium freeze when they are too far from the sun
what is the elemental composition of the universe vs earth (roughly)?
universe => hydrogen & helium
earth => silicon, oxygen, & iron
felsic vs mafic
felsic => high Al, Si
mafic => high Mg, Fe
lithosphere
crust + uppermantle
- felsic/mafic depending on crust on top
- brittle
aesthenosphere
upper mantle under lithos that convects
- ultramafic
- ductile
convection (geology)
density driven flow because of Hadley cells => as rock heats up & expands, it rises. when it hits the surface, it cools, gets denser, and sinks
continental crust
felsic, brittle, light (won’t submerge)
oceanic crust
mafic, brittle, heavy (will always submerge)
plate tectonic theory
Lithosphere split into 12 major plates
geothermal gradient & why
crust gets 20-30C warmer per km down
why => high pressure, residual heat from accretion (formation), radioactive decay (U, Th, K)
why is the earth a bar magnet?
the core has swirling Fe, Ni => generates electric currents
- dipole, field lines from south to north, which have REVERSED b4
alfred wegener
continental drift
- continental fit
- related rocks along cont. borders
- matching geology (mnts)
- fossil records
- NO ONE BELIEVED HIM BC HE WASNT A GEOLOGIST bc he was j a guy
midatlantic ridge & how was it discovered
divergent boundary (heart) found bc US wanted to hide nuclear subs (heart eyes) so they mapped the ocean
evidence:
- drilling in 60’s revealed no sediment on ridge but thicker towards continents
- rock dating revealed ridge is super young, older towards continents
- magnetism - rocks w/ Fe show poles reversing (same on each side)
marine magnetic anomalies
magnetometer measures magnetism as ship crosses ocean, its weird b/c of earth’s magnetic field and iron in rocks showing poles reversal
divergent boundary
constructive, 2 plates move away from mid-ocean ridge, shallow earthquakes
convergent boundary
destructive, 2 plates move towwards each other, denser oceanic subducts
=> mountains & volcanoes on the top plate form because the plate lifts up
=> OC-OC forms deep trenches bc both want to subduct
accretionary prism
sediment build up at a convergent boundary
transform boundary
2 plates slide past each other at a verticle fault
=> offset drain - when a stream’s flow is broken by transform boundary
continental rift
- continental crust stretches & thins
- breaks & forms faults
- parts of crust break & fall into rift valleys (low areas)
- aesthenosphere melts & rises, magma erupts out of volcanoes
5a. continues: plate splits in 2
5b. stops: rift fills w/ sediment
3 forces that cause lithosphere to move
- convection: rising & sinking currents in the mantle
- ridge-pull force: slope of lithosphere near ridge pushes outward from ridge
- slab-pull force: heavy lithosphere pulls down the rest of the plate in subduction
continental collision
OC-CC, when the oceanic part of OC all subducts, the land part of the OC crashes into the CC => forms a HUGE mountain range
where in the earth’s layers and what type of boundary are these earthquakes [33-70km, 70-700km] at?
- 33-70km: crust, divergent or transform
- 70-700km: mantle, convergent
hot spots & island chains
heat rising from the core rises through the mantle and melts the rock => crust is pierced and erupts w/ magma; island chains form from hotspots bc the crust moves but the hotspot still erupts, creating an island chain
how were the himalayas formed?
India (CC) crashed into asia (CC)
why does the pacific ocean grow faster than the atlantic ocean?
slab-pull from subduction
minerals
naturally occuring solid w/ orderly structural arrangement & definite chemical composition
magma & formation
- liquid rock below the surface,
- formation: decompressional melting - when hot mantle rock rises as pressure decreases, it melts
- can cool at depth in lithosphere ex: granite
lava
- liquid rock above the surface
- can cool quickly at earth’s surface ex: basalt
how can you melt rock?
- water (liquifies minerals)
- heat
- decreasing pressure
why is the mantle solid (even tho it’s super hot)?
PRESSURE
types of mineral structures
in chronological order (as magma cools)
- independent/isolated: ionic
- single chain: mix
- double chain: mix
- sheet: mix
- framework: covalent (but it can also form first idfk)
bowen’s reaction sequence w/ strucutrew/ mafic/felsic
- mafic: olivine (isolated), pyroxene (single chain), Ca-rich plagioclase (framework)
- intermediate: amphibole (double chain), micas (sheet), Na-rich plagioclase (framework)
- felsic: K-rich feldspar (framework), muscovite mica (sheet), quartz (framework)
fractionalized crystallization
minerals will cool & fall out of liquid rock
igneous rocks (intrusive)
- intrusive: magma, large & coarse grain from slow cooling
> felsic: pink & light grey
>mafic: dark grey & black
in mafic => felsic order…
gabbro, diorite, granite
why are igneous rocks geologically constructive?
they are always found where new rock is being formed (hot spots, divergent boundaries, convergent boundaries, continental rifts), crust is being built w these
where are volcanoes
hotspots, divergent boundaries, convergent boundaries, continental rifts
why is the Seirra Nevada mnt range felsic even tho its a OC-CC boundary (mafic lithosphere melted to form it)?
- partial melting (bottom of BRS aka felsic melts first)
- felsic sediments (sand) from OC melts
- crustal assimilation (felsic parts of crust melt first)
why do mafic rocks make up the sea floor?
oceanic crust is mafic durr
andesites
volcanoes make of intermediate rocks, lots of them at subduction zones (around the pacific)
how does glass form :D
lava cools SUPA quickly
divergent igneous composition
mafic, basalt over gabbro
convergent igneous composition
intermediate/felsic, andesite & diorite and/or rhyolite & granite
hot spot igneous composition
OC: basalt
CC: any
continental rift igneous composition
any :D
regolith
rubble/break down from erosion
what are joints in rocks
cracks from change in pressure
physical weathering
- frost wedging
- root wedging
- thermal expansion
- animal attack
chemical weathering
- dissolution: water molecules surround ions in minerals
- hydrolysis: reaction with water changes minerals into new ones
- oxidation: oxygen combines with iron in minerals to form weak, rusty minerals ew
- hydration: minerals expand when absorbing water
igneous structure vs sedimentary structure
- igneous: form when melt cools, chrystalline (interlocking grains)
- sedimentary: form when grains of preexisting rock stick together, clastic (cementic rocks)
sedimentary rocks (near to source)
conglomerate:
- grains 2mm+
- fragments rounded
- mix of quartz, feldspar
- mountains
breccia:
- grains 2mm+
- angular clasts
* gravity driven transport
- landslides
sedimentary rocks (far from source) (sandstones)
> 0.0063-2mm grains
well sorted
moderate energy environments (beaches, dunes, rivers)
arenite:
- grains rounded
- 90% quartz
* long distance transport
lithic sandstone:
- quatz, feldspar, rock fragments
* short distant transport
arkose sandstone:
- 25% orthoclase feldspar
* short distance transport
sedimentary rocks (far from source)
(non-sandstones)
> well sorted
low energy environment
siltstone:
- 0.004-0.0063 grains
- feels gritty
- typically quartz
- lakes, delta, beaches
mudstone & shale:
- <0.004mm grains
- mostly clay
- deep water
- shale is LAMINATED
- mudstone breaks up into blocks
- shale breaks into thin sheets
igneous rocks (extrusive)
- lava, fine grain from fast cooling
> felsic: pink & light grey
>mafic: dark grey & black
in mafic => felsic order…
basalt, andesite, rhyolite
sedimentary (biochemical)
fossiliferous limestone:
- CaCO2
- wam, shallow seas
coal:
- carbon rich
- oxygen poor environments ex: swamps
cross beds
formed when currents change (sediments fall at different angles over time)
pitted grains
grains with indentations formed from grains crashing into each other in wind
how and where are metamorphic rocks formed?
- how: add heat and/or pressure to a rock
- where: subduction zones (H), hot spots (H), plate collision (H+P), bottom of sedimentary basin (H+P)
how does metamorphism change a rock?
texture:
- rechrystallization: clastic to bigger, interlocking grains
- plastic deformation: grains get squished
- foliation: minerals align perpendicular to stress (lots can lead to compositional banding) only when there is pressure
minerology:
- minerals like garnets can grow
shields (metamorphic rocks)
continental interiors where ancient high grade metamorphic rocks are exposed
what type of rock are the oldest rocks?
metamorphic
metamorphic rocks (foliated)
in order of increasing heat&pressure
slate:
- fine grains
- some foliation
> shale + HP
phyllite
- fine grains
- some foliation
- bigga grains than ^^
schist
- coarse grains
- foliated
- bigga grains than ^^
gneiss
- coarse grains + garnets
- foliated => comp. bonding
- granite is often protolith
dropping shale vs slate on the table?
shale: thud, solid sounding
slate: pang, hollow sounding
metamorphic rocks (non foliated)
marble:
- calcite (CaO3)
> limestone + HP
quartzite:
- arenite +HP
greenstone:
- mafic minerals
> basalt + HP
where does metamorphism occur?
- mid ocean ridge (hydrothermal vents give heat)
- igneous intrusion (under volcano, rising plutons)
- subduction zone (pressure = foliation)
