earths internal structures

8/12/2019 Earths Internal Structures

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Earths Structure


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Origin of the Earth

Meteors and Asteroidsbombarded the Earth

Gravitational compression

Density Stratified planet


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Earths InteriorCore

dense

Iron and Nickel

Inner Core - solid

Outer Core - liquid

Less dense than core

Iron and Magnesium silicates

Mostly solid

Upper mantle is partially molten

Mantle

Outermost layer

Very thin and rigid

Continentalgranite Density = 2.8 g/cm3

Oceanicbasalt Density = 3.0 g/cm3

Crust


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Evidence of Internal Structure

Granite

Densitycalculate density of EarthSpeculate on probable compositions

Basalt

Meteorites Use composition and age to

determine composition and age ofEarth

Seismic wavesTravel times and direction give

indication of internal structure ofEarth


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Types of Seismic Waves

S waves

P waves

Primary waves

Push and pull movement

Travel fastest (~ 6 km/sec)

Travel thru solids and liquids

Secondary waves Move side-to-side

Slower (~ 4 km/sec)

Travel thru solids only
http://localhost/var/www/apps/conversion/tmp/Tectonics/S_Wave.MOVhttp://localhost/var/www/apps/conversion/tmp/Tectonics/P_Wave.MOV


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Seismic Waves Through Earth


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Lithosphere

Consists of continental,oceanic and upper part ofmantle

Continents composed of granite-

type rock, quartz and feldsparminerals, density+2.8g/cm3

Oceanic crust formed of basalt;basalt rich in iron/magnesiumminerals, density+3.0 g/cm3

Lithosphere is rigid layer ofcrust and mantle overlyingpartially-molten asthenosphere


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Continental Drift Evidence

Geographic fit of continents

Fossils

Mountains

Glaciation

Evidence supporting the idea that the continents had drifted.

Researchers noted geographic fit of continents e.g. Africa and S. America Atlantic formed by separation of Africa from S. America

Seuss, 1885, proposed super continent by studying fossils,rocks, mountains

Wegener and Taylor, early 1900s, proposed continental driftand Pangaea


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Continental DriftGeographic Fit

Continents seem to fit together like pieces of a puzzle
http://localhost/var/www/apps/conversion/tmp/Tectonics/PangeaBreak.MOV


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Continental DriftFossils

Similar distribution of fossils such as theMesosaurus


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Continental DriftMountains

Mountain ranges match across oceans


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Continental DriftGlaciation

Glacial ages and climate evidence


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Continental Drift ModelProblems

Alfred Wegener

Did not provide a

plausible mechanism toexplain how continentsdrifted

Presented research to

professionals


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Seafloor Spreading

Continental drift reexamined in 1960s with newinformation

World seismicity

New theory developedSeafloor spreading

Supporting evidence for seafloor spreading

Theory combining continental drift and seafloor spreadingtermed Plate Tectonics

Volcanism

Age of seafloor

Heat flow

Paleomagnetism


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Seafloor Spreading

New sea floor created at the mid-ocean ridge

and destroyed in deep ocean trenches


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Evidence for Seafloor SpreadingWorld Seismicity

Earthquake distribution matches plate boundaries


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Evidence for Seafloor SpreadingVolcanism

Volcanoes match some plate boundaries; some arehot spots


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Evidence for Seafloor SpreadingAge of Seafloor

Youngest sea floor is at mid-ocean ridge

Oldest sea floor away from mid-ocean ridge


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Evidence for Seafloor SpreadingPaleomagnetism

When rocks cool at the Earths surface, they record Earthsmagnetic field (normal or reverse polarity)

Earth has a magnetic field - Probably caused by rotation ofsolid inner core in liquid outer core (both mostly Fe)


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Evidence for Seafloor SpreadingPaleomagnetism

Paleomagnetic studies indicate alternatingstripes of normal and reverse polarity at the

mid-ocean ridge.


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Seafloor SpreadingHeat Flow


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Seafloor SpreadingConvection Currents

In 1960, proposed as driving force to move continents


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Theory of Plate Tectonics

John Tuzo Wilson combined ideas of continental

drift and seafloor spreading into Plate Tectonics


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Principles of Plate Tectonics

Earths outermost layer composed of thinrigid plates moving horizontally

Plates interact with each other along theiredges (plate boundaries)

Plate boundaries have high degree of tectonicactivitymountain buildingearthquakes

volcanoes


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Plate BoundariesThree types

Divergent

Convergent

Transform


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Plate BoundariesDivergent

Plates move away from each other

New crust is being formed
http://localhost/var/www/apps/conversion/tmp/diverg%20-%20african%20rift.mov


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Divergent Plate BoundariesExamples

East African Rift Mid-Atlantic Ocean Ridge


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Plate BoundariesConvergent

Plates are moving toward each other

Three Types:

Ocean-continent

Ocean-ocean

Continent-continent

Crust is being destroyed
http://localhost/var/www/apps/conversion/tmp/converg%20-%20himalayas.movhttp://localhost/var/www/apps/conversion/tmp/subduc%20-%20andes.mov


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Convergent Plate BoundariesExamples

Mount Lassen, California

Andes, South America

Mount Fuji, Japan


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Plate BoundariesTransform

Plates slide past one another

Crust is neither created nor destroyed

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http://localhost/var/www/apps/conversion/tmp/trans%20-%20san%20andreas.movhttp://localhost/var/www/apps/conversion/tmp/trans%20-%20san%20andreas.movhttp://localhost/var/www/apps/conversion/tmp/trans%20-%20san%20andreas.mov


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Transform Plate BoundariesExamples

San Andreas Fault

Calexico, California

Carrizo Plains Central California
http://localhost/var/www/apps/conversion/tmp/Tectonics/sm02Pac-NoAmflat.mov

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