P1: Earth in The Universe

• 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.

• 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.

Thin rocky crust:

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

Mantle:

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

Core:

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

• 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.

• 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.

• 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. 
• Subduction - when 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.

• 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.

• 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.

• Amplitude (distance from trough to top/bottom)
• Wavelength (distance between waves at highest/lowest point)
• Frequency (waves per second in hertz)

• 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.

Wave speed = Frequency x Wavelength

     (m/s)                 (Hz)                 (m)

Distance = Wave speed x Time

     (m)              (m/s)              (s)

• 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.

• 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.

• Approximately 14,000 million years old.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.