P1: Earth in The Universe


Seafloor Spreading

  • Mantle is solid beneath crust.
  • Liquid futher down.
  • Convection currents in mantle cause magma to rise.
  • Moves solid mantle and tectonic plates.
  • Magma reaches surface and hardens, forms new area of seafloor and pushes old floor outwards.
  • Seafloor spreads by few cm every year.
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The Earth

  • Molten when formed.
  • 4500 mil years old.
  • Learn about Eath structure by studying rocks.
  • Earth changed by:
    • Erosion: rock layers with oldest at bottom.
    • Craters: moon has craters from metoers.
    • Mountain formation: if no new mountains formed, Earth's surface erode to sea level.
    • Folding: some rocks folded from huge force over time.
  • Evidence of Earth's age, study:
    • Fossils of plants and animals in sedimentary rock.
    • Radioactivity of rocks which decreases over time.
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Structure of Earth

Thin rocky crust:

  • 10 - 100km thick.
  • Oceanic crust beneath oceans.
  • Continental crust forms continents.


  • Extends halfway to Earth's centre.
  • Higher densisty than crust's rock.
  • Hot, under pressure.


  • Over half of Earth's radius.
  • Nickel and iron.
  • Liquid outer, solid inner.
  • Radioactive element's decay releases energy and keeps hot.
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Continental Drift

  • Wegener's theory.
  • Continents had jigsaw fit.
  • Fossils of same animal on different continents.
  • Stated that continents separated and drifted.
  • Stated when 2 continents collided, forced upwards to make mountains.
  • Geologists didn't accept: Wegener was outsider, limited evidence.
  • Seafloor spreading evidence convinced scientific communtiy that Wegener correct.
  • Became accepted theory through peer review process.
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Tectonic Plates

  • Crust in several large pieces.
  • Float on mantle.
  • Can move apart, towards or slide past others.
  • Plates meet at plate boundaries where volcanoes, earthquakes, mountains occur.
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Plate Tectonics

  • Earth magnetic field changes polarity every mil years.
  • Combined with seafloor spreading, causes rock stipes of alternating polarity.
  • Geologists see how quickly crust forming by width of stripes. 
  • Subductionwhen oceanic and continental plates collide and denser oceanic forced under continental plate.
  • Oceanic plate melts, molten rock rises to form volcanoes. At destructive plate boundaries.
  • Mountain ranges along colliding plate boundaries as sedimentary rock forced up by pressure of collision.
  • Earthquakes occur most at plate boundaries:
    • Plates slide past or collide
    • Pressure builds up as plates push on each other
    • Eventually stored energy released and waves of energy spread from epicentre
  • Plate movement crucial in rock cycle:
    • Old rock destroyed through subduction.
    • Igneous rock formed when magma reaches surface.
    • Plate collisions produce high temperatures and pressure - rock folds.
    • Sedimentary becomes metamorphic.
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Waves from Earthquakes

  • Earthquakes produce wave motions on surface and in Earth.
  • Detected using seismograph.
  • Primary waves (P-waves):
    • Faster than S-waves.
    • Travel through liquids and solids.
    • Travel through liquid of outer core.
    • Longitudinal.
  • Secondary waves (S-waves)
    • Only through solids.
    • Can’t travel through liquid of outer core.
    • Transverse.
  • P-waves and S-waves travel at different speeds in rocks of different density.
  • If rock has high density, wave travels faster.
  • Boundaries between different types of rock lead to changes in wave speed.
  • Causes refraction or reflection of waves.
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Types of Wave

  • Longitudinal
    • Particles vibrate backwards and forwards from normal position.
    • Particles move backwards and forwards in same plane as direction of wave movement.
    • Sound travels as longitudinal waves.
  • Transverse
    • Particles vibrate up and down from normal position.
    • Moves up and down at right angles to direction of wave movement.
    • Light and water ripples travel as transverse waves.
    • All electromagnteic waves are transverse.
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Wave Features

  • Amplitude (distance from trough to top/bottom)
  • Wavelength (distance between waves at highest/lowest point)
  • Frequency (waves per second in hertz)(http://dev.physicslab.org/img/3e167420-7c93-4f76-a14f-c2ca1bf624db.gif)
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Wave Speed and Frequency

  • If wave travels at constant speed:
    • Increasing frequency will decrease wavelength.
    • Decreasing frequency will increase wavelength.
  • Frequency is inversely proportional to wavelength.
  • If wave has constant frequency:
    • Decreasing wave speed will decrease wavelength.
    • Increasing wave speed will increase wavelength.
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Wave Equation

Wave speed = Frequency x Wavelength

     (m/s)                 (Hz)                 (m)

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Distance a Wave Travels

Distance = Wave speed x Time

     (m)              (m/s)              (s)

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The Solar System

  • Formed 5000 mil years ago.
    • Started as dust and gas clouds, pulled together by gravity.
    • This made intense heat - nuclear fusion and Sun born.
    • Remaining dust and gas formed smaller masses, attracted to sun.
  • Smaller masses:
    • Planets - large masses, orbit Sun.
    • Moons - small masses, orbit planets.
    • Asteroids - small rocky masses, orbit Sun.
    • Comets - small icy masses, orbit Sun.
    • Dwarf planets - small masses, orbit Sun.
  • Planets, moons and asteroids move in elliptical orbits.
  • Comets move in highly elliptical orbits.
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The Sun

  • 500 million years older than Earth.
  • Energy from nuclear fusion:
    • Hydrogen atoms fuse together to produce atom with larger mass.
    • Binding energy stored in hydrogen atoms is released.
  • All chemical elements larger than helium formed by nuclear fusion in earlier stars.
  • Nuclei of hydrogen atoms fuse together during nuclear fusion.
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The Universe

  • Approximately 14,000 million years old.
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Speed of Light

  • Light travels at high but finite (limited) speeds.
  • If distance great enough, speed of light can be measured.
  • Speed of light through space 300000km/s, takes just over 1 second to reach moon.
  • Sunlight takes 8 mins to reach Earth.
  • Space distances measured in light-years.
  • Nearest galaxy to Milky Way is 2.2 mil light-years away.
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Measuring Distances in Space

  • Relative brightness– thedimmer a star, thefurther away but never certain.
  • Parallax– stars in near distance appear to move against background of distant stars, the closer they are, more they appear to move. Further away the star, less accurate measurement.
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Distant Stars

  • Radiation from stars tells us what we know about them.
  • Stars produce visible light, ultraviolet and infrared.
  • Light pollution when electric lights on Earth make viewing stars difficult.
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Other Galaxies

  • If source of light is moving away, wavelengths longer than if source is stationary.
  • Wavelengths of light from nearby galaxies longer than scientists expect so galaxies moving away.
  • Observations by Hubble showed:
    • Almost all galaxies moving away.
    • The further away they are, the faster they’re moving.
  • Hubble’s Law: The speed that galaxy's moving away proportional to its distance from us.
  • This means the Universe is expanding.
  • If an electromagnetic wave appears longer than it should, been red shifted so moving away.
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Relative Sizes to Universe

  • Diameter of Earth = 12742km.
  • Diameter of Sun = 110 x Earth’s diameter.
  • Size of Earth’s orbit = 107 x diameter of Sun.
  • Distance of Sun to nearest star = 4 light-years.
  • Size of solar system = several thousand light-years.
  • Size of Milky Way = 100000 light-years.
  • Distance of Milky Way to nearest galaxy = 2.2 million light-years.
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The Beginning and The End

  • Big Bang theory says Universe began with huge explosion 14000 million years ago.
  • If there isn’t enough mass, the Universe will keep expanding.
  • If there’s too much mass the Universe will collapse.
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