Plate TectonicsPlate TectonicsPlate TectonicsPlate Tectonics

Origin of UniverseOrigin of Universegg Big Bang modelBig Bang model (Hubble, (Hubble, 19291929) ) -- The The

ni erse began ith an e plosi eni erse began ith an e plosi euniverse began with an explosive universe began with an explosive expansion of matter, which later became expansion of matter, which later became what we know as stars planets moonswhat we know as stars planets moonswhat we know as stars, planets, moons, what we know as stars, planets, moons, etc. This event is thought to have etc. This event is thought to have occurredoccurred 1010 1515 billion yrs agobillion yrs agooccurred occurred 10 10 -- 15 15 billion yrs ago. billion yrs ago.

Nebular Hypothesis (Kant, Laplace 1796) - Earth and the other bodies of our solar system (Sun, moons, etc.) formed from a “vast cloud of dust and gases” called a nebula.

Big bang theoryBig bang theory

•There was a big bang some 15 billion years ago when the size of the universeyears ago, when the size of the universe was zero and the temperature was infinite. The universe then started expanding at near li ht dlight speed.

•At about 10,000 years after the Big Bang, the temperature had fallen to such an extentthe temperature had fallen to such an extent that the energy density of the Universe began to be dominated by massive

i l h h h li h d hparticles, rather than the light and other radiation which had predominated earlier. This explains the formation of galaxies and p gother large-scale structures observed in universe today.

Nebular HypothesisNebular Hypothesis•According to this hypothesis,

Nebular HypothesisNebular Hypothesis

the nebular cloud consisted of H and He, and a small percentage of the heavierpercentage of the heavier elements we find in the solar systemsystem

•Within the rotating disk, the rocky material and gasesrocky material and gases began to nucleate and accrete into protoplanetsp p

F ti f E th’ I t iF ti f E th’ I t iFormation of Earth’s InteriorFormation of Earth’s Interior•As Earth was formed it was extremely hot•As Earth was formed, it was extremely hot from the bombardment of space debris, radioactive decay and high internal pressuresradioactive decay, and high internal pressures.

•These processes caused Earth’s interior to melt, and then to differentiate into regions of chemical and physical differences as it cooled.

Layers of the EarthLayers of the EarthLayers of the EarthLayers of the Earth

C tC t Crust: Crust: Continental crust (Continental crust (2525--40 40

kmkm)))) Oceanic crust (~Oceanic crust (~6 6 km)km)

MantleMantleU tl (U tl (650650 k )k ) Upper mantle (Upper mantle (650 650 km)km)

Lower mantle (Lower mantle (2235 2235 km)km) CoreCoreCoreCore

Outer core: liquid (Outer core: liquid (2270 2270 km)km) Inner core: solid (Inner core: solid (1216 1216 km)km)

Values in brackets represent the approximate thickness of each layer

Layers of the EarthLayers of the EarthThe earth is divided into four main layers: Inner core, outer core, mantle and crust.

The core is composed mostly of iron (Fe) and is so hot that the outer core is molten, with about 10% sulphur (S) The inner core is under such extreme pressure that(S). The inner core is under such extreme pressure that it remains solid.

Most of the Earth's mass is in the mantle, which is ,composed of iron (Fe), magnesium (Mg), aluminum (Al), silicon (Si), and oxygen (O) silicate compounds. At over 1000 degrees C the mantle is solid but can deform1000 degrees C, the mantle is solid but can deform slowly in a plastic manner.

The crust is much thinner than any of the other layersThe crust is much thinner than any of the other layers, and is composed of the least dense calcium (Ca) and sodium (Na) aluminum-silicate minerals. Being relatively cold the cr st is rock and brittle so it can fract re in

Continental driftContinental driftContinental driftContinental driftTheory that continents and plates move Theory that continents and plates move on the surface of the Earth proposed by on the surface of the Earth proposed by Alfred Wegener in Alfred Wegener in 19151915..

Alfred WegenerAlfred WegenerAlfred WegenerAlfred Wegener

Maps by Wegener (Maps by Wegener (19151915), showing ), showing ti t l d iftti t l d iftcontinental driftcontinental drift

Th f ti t l d iftTh f ti t l d iftTheory of continental driftTheory of continental drift

Evidence for continental driftEvidence for continental driftEvidence for continental driftEvidence for continental drift

Matching coastlinesMatching coastlines Matching coastlinesMatching coastlines Matching mountainsMatching mountains

M t hi k t d kM t hi k t d k Matching rock types and rock agesMatching rock types and rock ages Matching glacier depositsMatching glacier deposits Matching fossilsMatching fossils

Evidence for continental driftEvidence for continental driftEvidence for continental driftEvidence for continental drift

Matching coastlines

Evidence for continental driftEvidence for continental driftEvidence for continental driftEvidence for continental drift

Matching mountainrangesranges

Evidence for continental driftEvidence for continental driftEvidence for continental driftEvidence for continental drift

Matching rockrock types and ages of rocksrocks

Evidence for continental driftEvidence for continental driftEvidence for continental driftEvidence for continental drift

Matching glacierMatching glacierdeposits 300million yearsagoago

Evidence for continental driftEvidence for continental driftEvidence for continental driftEvidence for continental drift

Fossils of of Mesosaurus (aquatic reptile) found on(aquatic reptile) found on both sides of Atlantic

Theory of Plate tectonicsTheory of Plate tectonicsTheory of Plate tectonicsTheory of Plate tectonics The theory of Plate tectonics was proposed in The theory of Plate tectonics was proposed in y p py p p

19601960s based on the theory of continental drift.s based on the theory of continental drift. This is the Unifying theory that explains the This is the Unifying theory that explains the

f i d d f i f h E h’f i d d f i f h E h’formation and deformation of the Earth’s formation and deformation of the Earth’s surface. surface.

According to this theory continents are carriedAccording to this theory continents are carried According to this theory, continents are carried According to this theory, continents are carried along on huge slabs (plates) on the Earth’s along on huge slabs (plates) on the Earth’s outermost layer (Lithosphere).outermost layer (Lithosphere).

Earth’s outermost layer is divided into Earth’s outermost layer is divided into 12 12 major major Tectonic Plates (~Tectonic Plates (~80 80 km deep). These plates km deep). These plates move relative to each other a few centimetersmove relative to each other a few centimetersmove relative to each other a few centimeters move relative to each other a few centimeters per year.per year.

Earth’s magnetic fieldEarth’s magnetic fieldEarth s magnetic fieldEarth s magnetic field

B i D t d iBasic Data used in formulating plate tectonics:

Magnetic stripes on the sea-floor. Magnetic field of Earth reverses on semi-regular basis. Minerals act like compass needles and ppoint towards magnetic north. “Hot” rocks record the direction of thethe direction of the magnetic field as they cool.

Tectonic plates of EarthTectonic plates of EarthTectonic plates of EarthTectonic plates of Earth

Types of plate boundariesTypes of plate boundariesTypes of plate boundariesTypes of plate boundaries

Divergent plate boundariesDivergent plate boundaries:: where plateswhere plates Divergent plate boundariesDivergent plate boundaries: : where plates where plates move apart move apart

Convergent Plate boundariesConvergent Plate boundaries:: where plateswhere plates Convergent Plate boundariesConvergent Plate boundaries: : where plates where plates come togethercome togetherT f l t b d iT f l t b d i h lh l Transform plate boundariesTransform plate boundaries: : where plates where plates slide past each other slide past each other

Types of plate boundariesTypes of plate boundaries

Divergent (Tension)Divergent (Tension)

Convergent (Compression)Convergent (Compression)

Transform (shearing)Transform (shearing)

Types of plate boundariesTypes of plate boundariesTypes of plate boundariesTypes of plate boundaries

Divergent Plate BoundariesDivergent Plate BoundariesDivergent Plate BoundariesDivergent Plate Boundaries Plates move awayPlates move away Plates move away Plates move away

from each other from each other (tension)(tension)

New lithosphere is New lithosphere is formedformed

normal faultsnormal faults Causes volcanismCauses volcanism not very explosivenot very explosive

Convergent Plate BoundaryConvergent Plate BoundaryConvergent Plate BoundaryConvergent Plate Boundary Plates move towardPlates move toward Plates move toward Plates move toward

each other each other (compression)(compression)

lithosphere is lithosphere is consumedconsumed

reverse/thrust faultsreverse/thrust faultsand foldsand folds Mountain buildingMountain building explosive volcanismexplosive volcanismpp

OceanOcean-- Continent convergent Continent convergent ii

OceanOcean--continentcontinent

marginmargin OceanOcean continent continent

plates collideplates collide Ocean plate Ocean plate pp

subducts below subducts below continentcontinent

Forms a subduction Forms a subduction zonezone

Earthquakes and Earthquakes and volcanoesvolcanoes

OceanOcean--ocean convergent ocean convergent marginmargin

2 2 oceanic plates collideoceanic plates collide One plate divesOne plate dives One plate dives One plate dives

(subducts) beneath (subducts) beneath otherother

Forms subduction zoneForms subduction zone Earthquakes andEarthquakes andEarthquakes and Earthquakes and

volcanoesvolcanoes

ContinentContinent--continent continent convergent marginconvergent margin

2 2 continental continental plates collideplates collide

Neither plate Neither plate wants to subductwants to subduct

Collision zone Collision zone forms high forms high

t it iexample: Himalayasexample: Himalayas

mountainsmountains Earthquakes, no Earthquakes, no

llvolcanoesvolcanoes

Himalayas: Continents collideHimalayas: Continents collide

Millions of years ago India and an ancient ocean called the Tethys Ocean were sat on a

l h ltectonic plate. This plate was moving northwards towards Asia at a rate of 10 centimeters per year. The Tethys oceanic crust was being subducted under the Asianwas being subducted under the Asian Continent. The ocean got progressively smaller until about 55 milion years ago when India 'hit' Asia Because both these continentalAsia. Because both these continental landmasses have about the same rock density, one plate could not be subducted under the other. The pressure of the impinging plates p p g g pcould only be relieved by thrusting skyward, contorting the collision zone, and forming the jagged Himalayan peaks

Transform plate marginTransform plate margin

Two plates slide past Two plates slide past p pp peach othereach other

strike slip faults. strike slip faults. Lithosphere is Lithosphere is

neither consumed neither consumed nor destroyed.nor destroyed.nor destroyed.nor destroyed.

Earthquakes, no Earthquakes, no volcanoesvolcanoes

Responsible for most Responsible for most of the earthquakesof the earthquakes

What drives plate movement?What drives plate movement?What drives plate movement?What drives plate movement?

Ultimately: heat transported from core andUltimately: heat transported from core and Ultimately: heat transported from core and Ultimately: heat transported from core and mantle to surfacemantle to surface

Heat transported by convectionHeat transported by convection Heat transported by convectionHeat transported by convection Core is ~Core is ~55,,000000°°C and surface is ~C and surface is ~00°°CC Where mantle rises: riftingWhere mantle rises: rifting Where mantle dives: subduction zonesWhere mantle dives: subduction zones