The Formation of the Earth

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The Formation of the Earth
http//www.youtube.com/watch?v_mcC8kFacrk (format
ion of the earth video, 5 min)

• The effects of gravity
• as the planet reached a diameter of about 350 km,
  the force of gravity became greater than the
  strength of rock.
• The center was crushed by gravity and the planet
  started to become round.

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The Formation of the Earth

• The effects of heat
• The collision of other objects generated heat
• Radioactive material generated heat
• Soon the interior began to melt

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How the Layers Formed

• As rocks melted, denser materials sank to the
  center of the Earth and became the core.
• Nickel, iron
• Less dense material rose to the surface and
  became the crust
• Oxygen, silicon, aluminum
• The middle layer is the mantle.
• Magnesium, iron
• http//www.youtube.com/watch?vH6OuD877Rog
• (formation of the Earth, 10 min)

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Earths Interior

• ODE Standard The composition and properties of
  Earths interior are identified by the behavior
  of seismic waves.

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The Crust

• A layer of solid rock that includes both dry land
  and the ocean floor.
• Very thin compared to the other layers, like the
  skin of an apple.
• Thickest under high mountains, thinnest under the
  ocean floor.
• 5-100 km thick
• Oceanic crust is denser than continental.

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The Mantle

• Made of very hot, solid rock.
• Lithosphere uppermost part of mantle and the
  crust together. Divided into tectonic plates.
• Asthenosphere less rigid (plastic). Softer
  part of the mantle, but still solid.
• Mesosphere lower mantle made of solid material
  that extends to the core.

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The Core

• Outer core molten (liquid) metal. Movements in
  this part of the core causes Earths magnetic
  field.
• Inner core dense ball of solid metal.
• Both are made of iron and nickel, but the extreme
  pressure in the inner core keeps the metal from
  becoming liquid.

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How do scientists know the structure of the Earth?

• Rock samples (direct evidence)
• Seismic waves (indirect evidence)
• Vibrations that travel through Earth carrying
  energy released during an earthquake.
• The speed and paths of waves reveal the structure
  of the planet.
• We will learn more about these later.

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Tectonic Plates

• ODE Standard Earths crust consists of major
  and minor tectonic plates that move relative to
  each other.

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A Giant Jigsaw Puzzle

• The lithosphere is made of plates that fit
  together like a puzzle.
• Vary in size and thickness.
• Float on the asthenosphere like ice floats in
  water.

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Wegeners Continental Drift Hypothesis

• Early 1900s
• Continental drift - continents once formed a
  single landmass, broke up, and drifted to their
  present locations.
• Pangaea existed about 245 million years ago.

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Sea Floor Spreading

• The process by which new oceanic lithosphere
  forms as magma rises to the surface and
  solidifies
• Evidence for continental drift
• Mid-ocean ridges are located where there is sea
  floor spreading.
• Example Mid-Atlantic Ridge

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Tectonic Plate Boundaries

• Three types
• Convergent plates collide
• Divergent where plates separate (mid-ocean
  ridges)
• Transform plates slide horizontally past each
  other (San Andreas Fault)

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Causes of Tectonic Plate Motion

• Changes in density within the athenosphere
• Energy comes from center of Earth
• Heated rock expands and rises (less dense)
• Cool rock contracts and sinks (more dense)

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How is it measured?

• In centimeters per year
• GPS (global positioning system) from satellites
• Scientists record the time it takes for GPS
  ground stations to move a given distance
• This allows them to measure the speed of the
  plates motion

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Deforming the Earths Crust

• Deformation the process by which the shape of a
  rock changes because of stress
• Stress the amount of force per unit area
• Compression stress caused by squeezing.
  Convergent boundary.
• Tension stress caused by stretching. Divergent
  boundary.

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Folding

• Bending of rocks because of stress
• Types
• Anticlines upward arching folds
• Synclines downward, trough-like folds
• Monocline both ends are horizontal

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Faulting

• The surface along which rocks break and slide
  past each other
• Types
• Normal usually with tension
• Reverse usually with compression
• Strike-slip opposing forces cause the rock to
  break and move horizontally.

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Earthquakes

• Occur along faults
• Caused by stressed rock during plate movement.
• Elastic rebound releases energy (remember elastic
  potential energy?).
• This energy travels as seismic waves.
• These waves cause earthquakes.

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Earthquake Zones

• Along tectonic plate boundaries where a large
  number of faults are located
• Example San Andreas Fault Zone in California

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A Brief Introduction to waves

• Parts of a wave
• Crest
• Trough
• Amplitude
• wavelength

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Waves Transfer Energy

• Transverse waves
• Particles vibrate perpendicular to the motion of
  the wave.
• Longitudinal waves
• Particles vibrate parallel to the motion of the
  wave.

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Behavior of Waves

• Diffraction
• Waves bend around an edge and spread out. Ex.
  Sound waves
• Refraction
• Waves bend as they pass from one medium to
  another because the speed changes. Ex. Straw in
  glass (light waves bending from air to water)

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Behavior of Waves

• Reflection
• Waves hit an obstacle and bounce off. Ex.
  Mirror
• Absorption
• Waves enter into a material and lose energy. Ex.
  Dark colored materials (blacktop)

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Behavior of Waves

• Constructive and Destructive interference
• Waves come together to create bigger or smaller
  waves.

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Seismic Waves

• P waves Pressure waves (or primary)
• Fastest, so they travel ahead of other waves and
  are the first to be detected.
• Can travel through all media (solid, liquid,
  gas).
• Move back and forth, which causes compression and
  tension.

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Seismic Waves

• S Waves Shear waves (or secondary)
• Second-fastest waves
• Cannot travel through parts of Earth that are
  completely liquid.
• Shear rock side to side as they travel forward.

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Seismic Waves

• Surface waves
• Move along the Earths surface (in the upper few
  kilometers) of the earths crust.
• Move the ground much like ocean waves.
• Travel the slowest.
• The most destructive.

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• S and P waves give scientists a picture of what
  is inside the Earth.
• P waves refract as they go from one layer of the
  earth to another
• S waves diffract when they hit something liquid
• http//earthquake.usgs.gov/earthquakes/eqarchives/
  year/2002/2002_11_03_waveani.php
• http//earthquake.usgs.gov/learn/animations/animat
  ion.php?flash_titleShadowZoneflash_fileshadowz
  oneflash_width220flash_height320
• http//science.discovery.com/tv-shows/greatest-dis
  coveries/videos/100-greatest-discoveries-the-core-
  of-the-earth.htm

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Earthquake Measurement

• Seismologist - a person who studies earthquakes
• Seismographs - instruments that record seismic
  waves
• Seismogram - the picture that is created by the
  seismograph

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Determining Time and Location

• Seismologists look at the seismogram to note the
  difference in arrival times of P waves and S
  waves
• Seismographs also help find the epicenter and
  focus

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Measuring Strength and Intensity

• Charles Richter created the Richter scale in the
  1930s.
• Measures the ground motion recorded by
  seismograms at seismograph stations.
• Magnitude - a measure of the strength of an
  earthquake
• Each unit on the Richter scale represents motion
  that is 10 times larger than the previous unit.
• A magnitude of 5 is ten times stronger than a 4.
• A magnitude of 6 is 100 times stronger than a 4.

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Modified Mercalli Intensity Scale

• Intensity - a measure of the degree to which an
  earthquake is felt by people and the amount of
  damage caused
• Uses Roman numerals I to XII
• I not felt, XII total damage of an area
• The number changes depending on where you are
  (highest number is close to the epicenter).

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Earthquake Forecasting

• Strength of earthquakes is related to their
  frequency (how often they occur)
• Scientists use this to help predict the strength,
  location, and frequency of future earthquakes

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Earthquake Forecasting

• The Gap hypothesis
• Sections of active faults that have had few
  earthquakes are likely to be sites of strong
  earthquakes in the future.
• These sites are called seismic gaps

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Earthquakes and Buildings

• Retrofitting - making older buildings more
  earthquake resistant
• Fasten it to its foundation
• Technology that improves earthquake resistance
• Mass damper
• Active tendon system
• Base isolators
• Cross braces
• Flexible pipes

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Volcanoes

• Types of volcanoes
• Shield volcanoes
• layers of lava released from nonexplosive
  eruptions.
• Ex. Hawaiis Mauna Kea (the tallest mountain on
  Earth)

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Types of Volcanoes

• Cinder cone volcanoes
• from moderately explosive eruptions.
• Ex. Paricutin in Mexico

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Types of Volcanoes

• Composite volcanoes
• most common
• From explosive eruptions.
• Ex. Japans Mount Fuji, Mount Rainier

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Other Volcanic Landforms
Caldera
Crater
Lava plateau
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Where Volcanoes Form

• Over plate boundaries
• Ex. Ring of Fire surrounding the Pacific Ocean
  (contains 75 of active volcanoes on land)
• 80 (on land) where plates collide
• 15 (on land) where plates separate

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Where Volcanoes Form

• Mid-Ocean Ridges
• Lava flows out to make crust
• Where most volcanic activity takes place
• Convergent boundaries
• During subduction, the temperature and pressure
  increase causing lava to form

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Where Volcanoes Form

• Hot spots
• Not along boundaries
• Above columns of rising magma, results of cracks
  in the crust
• Ex. Hawaiian Islands

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Predicting Eruptions

• Dormant and Active (not extinct)
• Monitoring earthquakes
• Studying volume and composition of volcanic gases
  (ratio of sulfur dioxide to carbon dioxide)
• Measuring slope and temperature
• GPS measures slope, infrared satellite images
  show temperature