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Earth’s Structure. Origin of the Earth. Meteors and Asteroids bombarded the Earth. Gravitational compression. Density Stratified planet. Earth’s Interior. Core. dense. Iron and Nickel. Inner Core - solid. Outer Core - liquid. Mantle. Less dense than core.

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Origin of the earth
Origin of the Earth

  • Meteors and Asteroids bombarded the Earth

  • Gravitational compression

  • Density Stratified planet

Earth s interior
Earth’s Interior

  • Core

  • dense

  • Iron and Nickel

  • Inner Core - solid

  • Outer Core - liquid

  • Mantle

  • Less dense than core

  • Iron and Magnesium silicates

  • Mostly solid

  • Upper mantle is partially molten

  • Crust

  • Outermost layer

  • Very thin and rigid

  • Continental – granite

    • Density = 2.8 g/cm3

  • Oceanic – basalt

    • Density = 3.0 g/cm3

Evidence of internal structure



Evidence of Internal Structure

  • Density

    • calculate density of Earth

    • Speculate on probable compositions

  • Meteorites

    • Use composition and age to determine composition and age of Earth

  • Seismic waves

    • Travel times and direction give indication of internal structure of Earth

Types of seismic waves
Types of Seismic Waves

  • P waves

  • Primary waves

  • Push and pull movement

  • Travel fastest (~ 6 km/sec)

  • Travel thru solids and liquids

  • S waves

  • Secondary waves

  • Move side-to-side

  • Slower (~ 4 km/sec)

  • Travel thru solids only


  • Consists of continental, oceanic and upper part of mantle

  • Continents composed of granite-type rock, quartz and feldspar minerals, density+2.8g/cm3

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

  • Lithosphere is rigid layer of crust and mantle overlying partially-molten asthenosphere

Continental drift evidence
Continental Drift Evidence

  • Researchers noted geographic fit of continents

    • e.g. Africa and S. America

    • Atlantic formed by separation of Africa from S. America

  • Geographic fit of continents

  • Fossils

  • Mountains

  • Glaciation

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

  • Wegener and Taylor, early 1900’s, proposed continental drift and Pangaea

  • Evidence supporting the idea that the continents had drifted.

Continental drift geographic fit
Continental Drift Geographic Fit

  • Continents seem to fit together like pieces of a puzzle

Continental drift fossils
Continental DriftFossils

  • Similar distribution of fossils such as the Mesosaurus

Continental drift mountains
Continental DriftMountains

  • Mountain ranges match across oceans

Continental drift glaciation
Continental DriftGlaciation

  • Glacial ages and climate evidence

Continental drift model problems
Continental Drift ModelProblems

  • Alfred Wegener

  • Presented research to professionals

  • Did not provide a plausible mechanism to explain how continents drifted

Seafloor spreading
Seafloor Spreading

  • Continental drift reexamined in 1960’s with new information

  • New theory developed – Seafloor spreading

  • Supporting evidence for seafloor spreading

  • World seismicity

  • Volcanism

  • Age of seafloor

  • Paleomagnetism

  • Heat flow

  • Theory combining continental drift and seafloor spreading termed “Plate Tectonics”

Seafloor spreading1
Seafloor Spreading

  • New sea floor created at the mid-ocean ridge and destroyed in deep ocean trenches

Evidence for seafloor spreading world seismicity
Evidence for Seafloor SpreadingWorld Seismicity

  • Earthquake distribution matches plate boundaries

Evidence for seafloor spreading volcanism
Evidence for Seafloor SpreadingVolcanism

  • Volcanoes match some plate boundaries; some are hot spots

Evidence for seafloor spreading age of seafloor
Evidence for Seafloor SpreadingAge of Seafloor

  • Youngest sea floor is at mid-ocean ridge

  • Oldest sea floor away from mid-ocean ridge

Evidence for seafloor spreading paleomagnetism
Evidence for Seafloor SpreadingPaleomagnetism

  • When rocks cool at the Earth’s surface, they record Earth’s magnetic field (normal or reverse polarity)

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

Evidence for seafloor spreading paleomagnetism1
Evidence for Seafloor SpreadingPaleomagnetism

  • Paleomagnetic studies indicate alternating stripes of normal and reverse polarity at the mid-ocean ridge.

Seafloor spreading convection currents
Seafloor SpreadingConvection Currents

  • In 1960, proposed as driving force to move continents

Theory of plate tectonics
Theory of Plate Tectonics

  • John Tuzo Wilson combined ideas of continental drift and seafloor spreading into “Plate Tectonics”

Principles of plate tectonics
Principles of Plate Tectonics

  • Earth’s outermost layer composed of thin rigid plates moving horizontally

  • Plates interact with each other along their edges (plate boundaries)

  • Plate boundaries have high degree of tectonic activity

    • mountain building

    • earthquakes

    • volcanoes

Plate boundaries three types
Plate BoundariesThree types

  • Divergent

  • Convergent

  • Transform

Plate boundaries divergent
Plate BoundariesDivergent

  • Plates move away from each other

  • New crust is being formed

Divergent plate boundaries examples
Divergent Plate BoundariesExamples

East African Rift

Mid-Atlantic Ocean Ridge

Plate boundaries convergent
Plate BoundariesConvergent

Three Types:

  • Ocean-continent

  • Ocean-ocean

  • Plates are moving toward each other

  • Continent-continent

  • Crust is being destroyed

Convergent plate boundaries examples
Convergent Plate BoundariesExamples

Mount Fuji, Japan

Mount Lassen, California

Andes, South America

Plate boundaries transform



Plate BoundariesTransform

  • Plates slide past one another

  • Crust is neither created nor destroyed

Transform plate boundaries examples
Transform Plate BoundariesExamples

San Andreas Fault

Calexico, California

Carrizo Plains, Central California