EOS 120 MID 1
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What is the source of earths internal heat?
Radiogenic heat - the radio active decay of unstable isotopes.
What are the isotopes - what do they decay into?
Uranium238&235 --------------> Lead
Potasium40 --------------------> Argon
Why is deep earth not a nuclear reactor?
Because the unstable isotope U, TH, K are in ppm. Trace amounts that provide just enough but not to much.
From the center out, name the 7 layers of earth
- 1. Iner Core - Solid
- 2. Outer core - liquid
- 3. lower mantel
- 4. upper mantel
- 5. Athenosphere
- 6. lithosphere
- 7. crust - oceanic thin & dense, contintel thick and bouyant.
How are condensation and accretion different in relation to the big bang
- BigBang was the birth of all elements.
- Condensation - elemental gases condesnse to for solids
- Accretion - they begin to colide and stick to gether to form increasingly larger rrocks, metors, planets.
What is an Isotope?
- Same number of protons diffrent number of nuetrons.
- thus they are unstable and decay
- they have a half life.
What is/are chondrites?
Whats so Significant about them?
- rare class of metorite
- most primitive objects in universe
- *same element ratios as the sun
NucleoSynthisis- Whats the proces
What elements are abundant on earth? Why?
- H - hydrogen
- He - Helium
- C - Carbon
- N - Nitrogen
- O - Oxygen
- Fe - Iron
- Some proton electron configurations are favoured some are not.
Most common metorites are made of ?
what happens if you melt a chondrite?
- A silicate liquid forms Si & O
- A metal Liquid forms Fe & Ni
How is a melted chondrite signigficant?
- It is very similar to the layers of earth
- outer layers are silica oxygen rich
- inner layers are iron nickel
what is the difference between terrestrial and juvian planets?
terestrial are closer to the sun, composed of rocky silicate mantel (mercury venus earth mars) high density planets, relitivly small
juvian further out lower temperatuire condenses H He, low density
Is there a relation between water & plate tectonics?
Yes, water erodes while tectonics build. If it werent for plate tectonics water would turn the earth flat.
-Rolling topography -Cloudy, thick atmosphere -High surface temp (200 C)
cold, windy -tremendous topography -volcanism -ice caps -water? (one time) -life? (maybe)
-water, ice -land, sea -rivers, lakes -continents -topography -temp gradient -humans
What can be said about plate tectonics, topography and planets?
Plate tectonics require internal energy, the lack of change in planets suggests they lack this internal energy or it has since died out.
Why is earth so different? 7 factors
- Just right distance from Sun to have water as either a solid, liquid and gas
- Water cycle – (closed system) • Results in a young regenerated surface
- Also enables life to evolve – exchange of gases and elements between earth and atmosphere
- Internal heat – radioactive decay of elements • Creates movements of surface
- Convection (movement) in solid rocky interior (over long periods acts as a liquid)
Some siesmic waves do not travel through water- which and what is significant about this?
S-waves do not travel through water because liquids lack shear strenght. We can record that s-waves do not travel through the outer core thus it must be liquid.
The story of plate tectonics/continetal drift.
- began when wegner proposed the thought that continets apear to fit together like a puzzle - they must have somehow drifted away - why are similar fossils found on different continents?
- Theory rejected - no proof of driving force - wegner not a geologist
1950's WWII - sea floor exploration for submarines identified amazing underwater topography (MOR
) Marrie thorp drew maps
magnetic patterns indicated sea floor spreading
now we have a driving mechanism
lines of evidence for continental drift (5 of em)
- 1. continental shelf margins fit like a puzzle
- 2. paleontology - fossils of things that canot swim or fly found across vast oceans
- 3. topography- folded mountain belts that end at one continent and begin on another.
- 4. glacial deposits - movement of glaciers leave distinct marks showing movement at the equator.
- 5. paleoclimatic belts - things formed only in warm climates are found in acient rocks at the poles (coal, limestone from coral)
sea floor spreading - what where why how
at MOR tension pulls the rock appart, magnetic patterns are recorded in the new earth, this is the driving mechanism for continental drift.
geodynamo & earth magnetism
- spinning electricly conductive (Fe) fluid creates a magnetic field.
- magnetic minerals align in new basalt to record the location of these magnetic poles. evidence of continetal drift and polar wander
details of magnetic stripping
- faster ridges - thicker stripes
- less reversal thicker stripes
paleo magnetism what and why?
- record of the magnetic pole recorded in rocks of different ages
- provides a history of continetal movement
how do we know a rock formed near the equator?
magnetic mineral aling in higher inclanation near the poles and lower almost horizontal inclanations near the equator
what are polar wander paths? what can they tell us?
- Over time the poles appear to wander all over the place specific to each continent
- if we account for continental drift/seafloor spreading they will in fact line up to a comon pole
plates & lithosphere vs athenosphere
plates are made of the rigid lithosphere, these "float" on the asthenosphere
convection - is it the driving force of drift/spreading?
of the asthenospher
is caused from the conductive cooling
of the lithosphere.
- rather the driving force is older cooler more dense oceanic crust subducts and creates tension which pulls apart the MOR. As the crust at the MOR becomes thiner it sinks creating the valley in the middle. (on continets this is the rift valley)
So what controls the rate of sea floor spreading?
which moves faster?
- The pacific moves much faster ~15cm/yr vs atlantic ~4cm/year
- this is because 1) it is older/more dense thus more "ready" to subduct. Also it surrounded by more subduction zones, thus there is more room for it to disapear...this is why there is the pacific ring of fire while the atlantic is calm volcanism.
why cant all plates expand?
It would make the earth huge and hollow.
anaology for spped of plate spread
finger nail growth
how do we study the sea floor
- samples from ocean drilling
what is an ophiolite?
ancient oceanic crust exposed on land.
what is an absyssal plain?
areas of the sea fllor 3-6km deep, inactive, high sedimentation. typically the area from the edge of the continetal slope to the MOR
what is the realtion ship between temperature and pressure
- the melting point increases with pressure
- i.e. it takes higher temperature to melt rocks under great pressure.
THIS IS WHY THE INNER CORE IS SOLID!
is a MOR active or passive?
It has active volcanism however it is a passive mantel upwelling.
dip angle - tell me about it
- this is the angle between the overiding(continetal plate) and the subducting plate.
- the older/denser a oceanic plate is the faster it subducts/the greater the dip angle.
how do new oceans form?
- at continental rift valleys
- tensions pulls and thins the plate, thus it begins to sink, this continues until a large basin forms...the red sea
what is the role of H2O in plate tectonics
- cold water sinks into cracks in the plate near a MOR. this water is heated, becomes element rich, some of it is expelled near the MOR (smokers)...
- Some water stays in the plate (bound in rock) and is cariied all the way to the subduction zone where it is realeased (through melting of the subducting plate)
- the water is hot and more bouyant so it rises into the overiding plate, lowering the pressure, allowing for melting, thus the volcanic belts like cascades, and why the eruptions are so explosive.
one "ocean volume" of water is recycled_________through the hydrothermal/ridge interaction
every 100 mil year
how does a continent grow? 2 ways
1. by area - continents colide, india nad the himalaya
2.by mass - new magma from sub zone. Hydrous minerals help to create differeing composition
what is the difference between stress and strain?
stress is the force strain is the result
i.e. stress creates strain
examples of convergent plate boundries
rockies, alps, andes, himalayas
- adjustment due to gravity
- crust bouyant, mantel dense
- iceberg/log in water analogy
brittle vs ductile
what determines it
brittle lose cohesion breaks/fractures
ductile perment lose of shape but doesnt break...it folds
Presure(depth) & strain rate
silly putty analogy
- units in pascal
- Presure= p*g*z
- p=density 2800kg/m3
- g=gravity 9.8 m/s2
- z= depth (m) 30,000m
three types of faults
- 1. normal - tension/pulling = verticle movement, hang wall down
- 2.reverse - compression/pushing hang wall up
- 3. slip lateral slide
rule of thumb for depth & pressure
3km = 1000bars = 1kbar = 0.1 gpa
what is the benioff zone?
area of subduction zone where deep earthquakes happen....proved subduction zones
earth quakes related to the three types of plate boundries
- 1. divergent - shallow narrow zone ~15km
- 2. transform - shallow
- 3. convergent - wider belt shallow, int, and deep D>100km
focus vs epicenter
- foucus is exact point
- epicenter is verticle translation to the crust
why are quakes in the upper 70km
because rocks under greater pressure are stronger. also more ductile
siesmic discontinuities (5 of em)
- MOHO - 35km crust/mantel boundry
- Low Velocity 100-250km mantel almost melted
- 410km phase change in mineral structure
- 660km phase change in minerals
- 2920 core mantle boundry
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