Download - 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
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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
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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
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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
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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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Transform Plate BoundariesExamples
San Andreas Fault
Calexico, California
Carrizo Plains Central California
http://localhost/var/www/apps/conversion/tmp/Tectonics/sm02Pac-NoAmflat.mov