EESB18H3 Lecture Notes - Geologic Time Scale, African Plate, Magnetic Anomaly Detector

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Published on 6 Oct 2012
School
UTSC
Department
Environmental Science
Course
EESB18H3
Professor
EESA05 Lecture 3: PY
Date:
1
Lecture 3: Plate Tectonics
How do we get the mountain formations, volcanoes etc; plate tectonics
Development of plate tectonic theory
Consequences of tectonics
Slide : Internal Energy
Whenever you have something moving, have to have NRG to actually move it
Early on, when planets formed, pretty much there were many rock masses that collided; these
collisions had to do with formation of planets
Each mass has lots of kinetic NRG associated w/ it, once collide w/ each other, the kinetic NRG
changes to thermal NRG; very hot
Thru heat differentiation and mass differentiation > Earth became bigger; middle = very hot;
then surrounding it cooled down; as you get to surface = cooler
o Density differentiation is what actually facilitates this; there are things that are less
dense than the iron core that’s in the middle
o The NRG of radioactive decay of core is what’s running the engine (plate tectonics)
Slide : Cross-Section of Earth
Very dense very hot = inner core
As you move out, get less dense and less hot materials
Radioactive heat thru mantle and the mantle sends that heat to the top layers
Top of mantle = asthenosphere
o Asthenosphere = hot but it’s not a liquid; it’s a very hot solid and because it’s under so
much pressure, even though it’s hot, it acts as plastic plasticity quality
o Heat rising, goes thru asthenosphere that’s very plastic and on top of the asthenosphere
is the lithosphere which is brittle and hard (not plastic)
o b/c asthenosphere is very hot and under pressure and has plastic quality, the
lithosphere rides on top of the asthenosphere
lithosphere = broken into bits = lithospheric plates and these plates float around on top of the
asthenosphere
on top of lithosphere = crust = what we walk on
o crust = 2 diff kinds
oceanic
continental
inner core outer core mantle top of mantle = asthenosphere (plastic) lithosphere =
broken into bits at the very top, what we see is the crust
radioactive NRG drives the bits of lithosphere and pushes them around
Lithospheric plates:
various lithospheric plates: African plate etc;
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EESA05 Lecture 3: PY
Date:
2
lithospheric plates are moving around
o some places where they’re moving away from one another = divergent boundaries
o some places where they’re moving towards one another = convergent boundaries
o it’s the moving away and towards one another that’s creating everything that we see
in the oceans, we have the oceanic crust; in the ocean, have mid-ocean ridges/rifts where in the
ocean, hot stuff comes up from the asthenosphere and comes onto the ocean floor and pushes
these oceanic crusts away from one another
o somewhere else, the oceanic plates may actually be colliding
o as plates hit, a lot may happen and it changes based on what kinds of plates we have
colliding
o whether 2 oceanic plates, one continental + one oceanic or 2 continental plates colliding
raw materials of the plates are constantly being recycled = this is part of the tectonic cycle
mid ocean ridge, for ex: Atlantic mid-ocean ridge and also have big one in pacific ocean
o also west coast of south America and North America
o mid-ocean ridge = not very high mountains but have volcanoes magma comes up and
out and pushes plates away
o stuff comes out of the ocean floor = basalt
basalt = really dark, lot of iron/magnesium, very dense
the rocks that we see on the continents aren’t as dense and heavy as the oceanic crust
the differences in density is very impt for what happens
Physics: To see how heat is actually distributed
which movement of NRG is actually impt for tectonic plate mvt?
Conduction
o At the molecular level, you have NRG that’s being passed on from one molecule to the
next
o In this way, get NRG transfer from one location to the next
o Vibration of atoms/mocs
o When adding heat to the pot, you’re increasing the vibration of the atoms of the moc in
that object
Convection
o By moving of anything that can flow, whether air/water/something plastic that’s how
you get the heat moving thru convection
Latent heat
o Very impt when considering heat transfer of ocean and atmosphere
o Water has the largest heat capacity of all the liquids/solids on the planet with the
exception of liquid nitrogen/ammonium
o Heat capacity: if you want to heat 1 kg of water (change it from liquid to vapour), you
have to add a LOT of NRG to change the phase of the water a wonderful quality of
water means that we can transfer that NRG
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EESA05 Lecture 3: PY
Date:
3
In oceans, within the depths of the ocean, hold a certain amount of NRG and
they distribute that NRG around the globe that’s how climate gets
moderated
o So, the water has all this heat and changes into vapour to change it back to liquid
form, it has to give away that heat that’s the latent heat that’s being transferred
o When it snows, actually feel that it’s not as cold; the water’s actually giving away that
latent heat to freeze up
Which heat movement is impt 4 plate tectonics?
o Convection
o Convection is what’s driving the transfer
Atlantic ocean is getting wider by 5cm/yr; opening up by 1mm every week
o The amount of NRG needed and the force = tremendous
o Arrows show the relative mvts of these plates and along some boundaries = moving
away from one another, or towards one another
o One place where you can see it colliding = Indian plate
India and Himalayas; have 2 continental plates colliding and giving rise to the
continental crust where you get the Himalayas
o Another place with collisions:
West coast of South America
Normasca plate = part of the Pacific Ocean is hitting West coast of South
America to form the Andes (oceanic plate hitting continental plate)
Convergent Margins
o 2 plates colliding
Divergent Margins
o Two plates are actually moving away from one another; can get this in the middle of the
ocean have hot magma from the asthenosphere coming out thru lithosphere &
oceanic crust and pushing apart the 2 plates
o Get destruction of crust
o Where you have divergence, you’re actually making new crust; deep down in mid-
oceanic ridge, have the basalt, magma coming out new crust formed
Transform Margins
o When you have some sort of change in the movement, where they’re not hitting or
moving away from one another
o Rather, they’re sliding/slipping past one another
o Along the mid-oceanic ridges, sometimes you get breakage (due to pressure etc;) that
ends up as transform faults
o Can have active or inactive transform faults
At one end, there’s destruction of crust, the other end = construction of new crust balance
In terms of aging:
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Document Summary

How do we get the mountain formations, volcanoes etc; plate tectonics. Whenever you have something moving, have to have nrg to actually move it. Early on, when planets formed, pretty much there were many rock masses that collided; these collisions had to do with formation of planets. Each mass has lots of kinetic nrg associated w/ it, once collide w/ each other, the kinetic nrg changes to thermal nrg; very hot. Very dense very hot = inner core. As you move out, get less dense and less hot materials. Radioactive heat thru mantle and the mantle sends that heat to the top layers. On top of lithosphere = crust = what we walk on: crust = 2 diff kinds. Basalt = really dark, lot of iron/magnesium, very dense the rocks that we see on the continents aren"t as dense and heavy as the oceanic crust the differences in density is very impt for what happens.

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