Geo 002 Midterm 2: Plate Tectonics

record of polarity reversals

-(1963) by Vine and Matthes verified seafloor spreading by studying the magnetic properties of the seafloor -the poles are fixed but every so often they switch, but we don't know why --->-Magnetic field gets weak and chaotic -average reversal takes 5000 years to completely reverse -the last pole reversal was around 780,000 years ago -Relate to extinctions: In absence of magnetic field or a weak magnetic field, we are not protected by solar wind, which has the capacity to erode the atmosphere of our planet

Mid-Atlantic Ridge

-A chain of volcanic mountains that are the site of seafloor spreading under the Atlantic Ocean. -technically the largest mountain chain in the world

lithosphere

-A rigid layer made up of the uppermost part of the mantle and the crust.

island arc

-A string of volcanoes that form as the result of subduction of one oceanic plate beneath a second oceanic plate along a deep-ocean trench -formed by convergent boundaries

convergent plate boundaries

-A tectonic plate boundary where two plates collide, come together or crash into each other.

convergent boundary

-A tectonic plate boundary where two plates collide, come together or crash into each other. -destructive boundary -related to subduction zones where one plate dives into earth's interior under the other plate

Ekman spiral

-A theoretical model of the effect on water of wind blowing over the ocean. Because of the Coriolis effect, the surface layer is expected to drift at an angle of 45° to the right of the wind in the Northern Hemisphere and 45° to the left in the Southern Hemisphere. Water at successively lower layers drifts progressively to the right (N) or left (S), though not as swiftly as the surface flow.

plate tectonics

-A theory stating that the earth's surface is broken into plates that move and change in size through time -a unifying theory of earth science combining the idea of continental drift and sea-floor spreading -the mantle is a flowing solid

accretionary prism

-A wedge-shaped mass of sediment and rock scraped off the top of a downgoing plate and accreted onto the overriding plate at a convergent plate margin.

hot spot

-An area where magma from deep within the mantle melts through the crust above it -Hawaii is a good example -seamounts and volcanic island (rising magma plumes originating deep within the mantle)-- Yellowstone, Hawaii -appear to remain relatively stationary while plates move across them = island chains; track rate and direction of plate movement -they are plumes of hot material/magma that originates deep within the mantle and rises towards the surface --->These plumes need not and often do not occur at plate boundaries --->They can be just in the middle of the lithosphere, away from plate boundaries -tell us about rate, direction, change in direction

divergent plate boundaries

-Areas where plates move away from each other, forming either mid-oceanic ridges or rift valleys -constructive -magma comes up from the boundary and creates new seafloor

benioff zone

-Distinct earthquake zone that begins at an oceanic trench and slopes landward and downward into Earth at an angle of about 30° to 60°. -a result of convergent boundary where subduction has occurred

Wegener

-German geophysicist who proposed the theory of continental drift (1880-1930) -pangea (1912) evidence: -fossils -continents fit like a puzzle (S. Amerca and Africa for example) -Similarities in rock types and structures on either side of the Atlantic ocean --->Shared mountain ranges between multiple continents --->All the result of the same mountain-building event -paleoclimate

ocean crust

-High density, young age, thin, and made of basalt ~5km thick -denser than continental crust

the gulf stream

-Latitudinal redistribution of energy: warm water moves north, cold water moves south -We have warm water coming from the gulf stream -Its just a string of warm water -Gulf stream comes through the straights of Florida then bends off the coast heading eastward by North Carolina -The gulf stream meanders and rings -The gulf stream keeps the south coast of England warm

thermohaline circulation

-Movement of ocean water caused by density difference brought about by variations in temperature and salinity. As ocean water freezes at the poles it concentrates salt, and the colder, denser water sinks. -responsible for deep ocean circulation

coastal upwelling

-Off the coast of California the dominant surface current flows south toward the equator. Ekman transport pushes water away from the coast, as the surface water moves away it is replaced by cooler (nutrient-rich) water from below. -These areas are characterized by high productivity -Surface Water is deflected to the right and pushed offshore, then cold water comes up and fills the vacuum created -This is why the west of America has cold oceans as compared to the east coast

Coriolis effect

-Particles in motion are all subject to the Coriolis effect -They are deflected to right in the northern hemisphere and the left in the southern hemisphere

transform boundaries

-Places where tectonic plates slide along beside one another as they move -california is an example -conservative -Fault- an area where the earth is ruptured

convection

-Process by which, in a fluid being heated, the warmer part of the mass will rise and the cooler portions will sink.

transform boundary

-The boundary between tectonic plates that are sliding past each other horizontally -result in Earthquakes -California is an example -Conservative- no new material made or old material consumed, strike-slip motion- they just slide past one another

divergent boundary

-The boundary between two tectonic plates that are moving away from each other -Constructive boundary -creates ocean ridges -New material is created when hot material rises through this this ridges

Wilson Cycle

-The cyclical opening and closing of ocean basins caused by movement of the Earth's plates. -Cycles of the formation and breakup of supercontinents -Occur on timescales of a few 100 million years- longest cyclical process on earth -Profoundly influenced many things on earth

continental drift

-The hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations -not accepted until 1950s -continents move through plate tectonics

sea-floor spreading

-The process by which molten material adds new oceanic crust to the ocean floor -mid-ocean ridges represent the upwelling portion of convection cells in the mantle and ocean trenches (subduction zones) represent the downward limbs -seafloor is young because it is constantly being renewed -Harry Hess said "ocean ridges represent the upwelling portion of convection cells in the mantle, and ocean trenches (subduction zones) represent the downward limbs (so seafloor is young-- constantly being renewed)" -oldest seafloor is only 200 million years old -responsible for moving continents around

vertical structure of oceans

-Thermocline- zone of rapid change from warm in the surface and cold in the deep -Halocline- salinity is low in surface oceans and pretty high in the deep ocean -Pycnocline- density is pretty low in the surface ocean

deep-ocean trench

-a deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle

mantle convection

-a recurring current in the mantle that occurs when hotter, less dense material rises, cools, and then sinks again. This current is believed to be one of the driving forces behind tectonic plate movement. -caused by radioactive decay of elements in the mantle and core

polar wander path

-this claim is not true because the poles have not moved, however it is defined as the Path to which it seems the poles may have moved. Says that polar wander paths are all the same -in reality, the continents moved, not the poles. Therefore wander paths are not the same -When polar wander paths for two diff continents are diff for the same time interval, it means those continents moved relative to a fixed pole- this shows us how they've moved

Liquid iron

-what is earth's outer core made out of

the differential heating of earth

-what is the combined effect of atmospheric and oceanic circulation driven by?

magnetic dynamo

-a theory that explains phenomena of the solar cycle as a result of periodic winding and unwinding of the Sun's magnetic field in the solar atmosphere -a mechanism that transforms energy from fluid motions (convection of liquid iron at Earth's core) into electrical currents that create a magnetic field -concept 1: Earth has a magnetic field -concept 2: Some minerals have the ability to record the magnetic field they existed in when they formed out of molten magma -the magnetic field is a centerpiece of developing and sustaining life on a planet -We have a magnetic field because early in our history the earth started to differentiate & as the earth cooled, vast portions became solid & The outer portion of the core became liquid The outer core has more sulfur than inner core so melting point is lower -EArth's interior is really hot due to radioactive decay. Constant decay of elements keeps the earth's interior warm -The movement of molten iron in the outer core that generates as sustains the magnetic field This is the mechanical energy is converted to electricity

active vs passive continental margins

-active continental margins are located at plate boundaries (subduction zones); passive continental margins are found at the edges of continents where there isn't a plate boundary (the oceanic crust and continental crust are part of the same tectonic plate).

thermohaline circulation

-an oceanic circulation pattern that drives the mixing of surface water and deep water -literally means temperature and salinity

mid-ocean ridges

-can be offset by Transform boundaries, occurring together

ocean-ocean and ocean-continent

-convergent boundaries where the ocean crust subducts beneath another plate boundary

earth's magnetic field

-deflects most of the solar wind whose charged particles that would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation -life on earth would not be possible without this -it protects us

bottom water

-formed at the poles -Densest water produced in the ocean -It's formed near poles were the surface ocean water freezes. As the water freezes, sea-ice is formed, but most of the salt is excluded from the ice. The cold water just beneath the ice becomes saltier and very cold -The combination of high salinity and low temp results in very dense water that sinks to the seafloor, from where it spreads toward the equator. -The two majors sites for bottom-water formation are the Weddell Sea of Antarctica (Antarctic Bottom Water, AABW) and the North Atlantic off Greenland (North Atlantic Deep Water, NADW)

"Ring of Fire"

-global distribution of volcanoes -Near plate boundary activities

convergence

-in a clockwise gyre in the northern hemisphere, the effect of the Ekman Transport is to push water to the center of the gyre

global hydrological cycle

-it's in a steady state -The volume of the ocean stays the same because the amount that leaves also comes back The inputs equal the outputs -water leaves salt behind when it evaporates -Most of Earth's water is in the ocean and that moves to land by evaporation

deep ocean circulation

-not influenced by winds -driven by thermohaline circulation

curie point

-point at which iron-bearing minerals solidify and give evidence of paleomagnetism -point at which a magnetic material, as it cools, lines up with the magnetic field present at that location -Iron-bearing minerals line up with the magnetic field -Below this point- eg 770 deg C for iron-- atoms that behave as tiny magnets spontaneously align themselves in certain magnetic materials

magnetic stripes

-provide evidence of sea floor spreading when they show the reversal of magnetic fields -Develop as new crust is added to the ocean floor at mid-ocean ridges and cool below the Curie Point, becoming magnetized according to the magnetic fields that exist at the time of cooling

declination

-provides direction to the magnetic pole -At any given spot on earth, the direction of the pole

inclination

-provides latitude (N-S) -describes tilt and tells how far one is from a pole

surface waves

-seismic waves that travel along the Earth's surface -can travel through solids only

body waves

-seismic waves that travel through the Earth's interior -can travel through solids and fluids

oceanic-oceanic

-subduction that leads to the formation of island arcs

seamount

-submarine volcano that does not rise above the water's surface

earthquakes

-sudden, violent movements of Earth's crust -located in a close relationship to plate boundaries

Arthur Holmes (1930)

-suggested that convection cells operating in the mantle could propel continents, explaining how the continents drift -proposed mantle convection as a driving mechanism around 1930

surface ocean circulation

-the pattern looks similar to winds -redistribute heat that is intense in equatorial regions

continent-continent subduction

-the result of this is mountain building when continental crust not effectively subducted -Himilayans are a great example also Alps and Appalachians -Appalachians are an example of when the Atlantic ocean closed up

paleomagnetism

-the study of changes in Earth's magnetic field, as shown by patterns of magnetism in rocks that have formed over time -iron-bearing minerals (when cool below Curie point) act as fossil compasses that point toward the existing magnetic poles -looking at genetic proposition of the earth and how they've changed over time -The study of the alignment of magnetic minerals in rock, specifically as it relates to the reversal of Earth's magnetic poles; also the magnetic properties that rock requires during formation (diverging boundaries)

continental crust

35 km deep -composed of granite -less dense than oceanic crust

oceanic crust

5 km deep -composed of basalt

ring of fire

A major belt of volcanoes that rims the Pacific Ocean

why is the sea salty

Salt in the sea is derived from the breakdown of crustal rocks on land (physical and chemical weathering) Water flowing over or through rocks remove soluble materials (ions). Rivers carry ions to the ocean (about 4 billion tons of dissolved rocks move into the ocean per year) An output of salt: When ocean water evaporates it leaves behind the salt Some of the evaporated water falls back on the land and eventually returns to the ocean with more ions, repeating the cycle The salinity of the ocean does not increase on average however because many processes remove salts from seawater: (formation of evaporate deposits, biological processes (formation of animals' shells), chemical reactions with the sea-floor). Input and removal are in balance (a steady state)

continental drift

The hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations

upwelling

The movement of deep, cold, and nutrient-rich water to the surface

downwelling

The movement of water from the surface to greater depths.

Continental crust

The portion of the earth's crust that primarily contains granite, is less dense than oceanic crust, and is 20-50 (35) km thick

Asthenosphere

The soft layer (solid that can flow under hot and high pressure) of the mantle on which the tectonic plates move -Convection cells move around under here and affect things in the Lithosphere -located under lithosphere

how long does it take for the ocean to circulate

it takes 1000 years for the ocean to completely circulate

tectonics

large-scale processes affecting the structure of the earth's crust.

subduction zone

the region where an oceanic plate sinks down into the asthenosphere at a convergent boundary, usually between continental and oceanic plates

sodium and chloride

the two dominant ions found is seawater

true

true or false: Radioactive decay in liquid core causes plate movement

benioff zone

when oceanic lithosphere dives beneath continental lithosphere a planar or flat zone of earthquakes is produced by the interaction of a downgoing oceanic crustal plate with a continental plate

subduction

where one plate is diving beneath the other