02.2 Earth

• Interstellar space is the region between stars. It hosts a vacuum (absence of matter, < 1 atom per litre)
• Cosmic rays are high-energy atomic nuclei ejected into space at extremely high velocity by supernova explosions
• Objects in the Solar System

  • Oort Cloud
  • Kuiper Belt
  • Asteroids (Trojans, Greeks, Hildas)
  • Planets

  
• Oort Cloud


  A diffuse cloud of icy particles held in by the Sun's gravity past Neptune's orbit

  
• Heliosphere


  Technically delimits the edge of the Solar System, and incorporates the Kuiper Belt and planets lie within it

  
• Most comets originate from the Kuiper Belt
• Neptune forms the outer boundary of the Kuiper Belt; inside this is interplanetary space

  
• Most asteroids lie between the orbit of Mars and Jupiter

  
• Some asteroids (known as the Trojans and the Greeks) border Jupiter's orbit, while the Hildas lie between the main asteroid belt and Jupiter

  
• Astronomical Unit (AU)


  Distance between Earth and Sun
• Terrestrial planets look markedly different from the gas giants as well as from each other
• Magnetic field


  The region measurably affected by the force emanating from a magnet

  
• Earth acts as a dipole or magnet with a north pole and a south pole

  
• Geographic poles


  Places where Earth's rotational axis intersects the planet's surface

  
• Magnetic poles


  Magnetic north lies near geographic south pole; magnetic south lies near geographic north pole

  
• Solar winds distort Earth's magnetic field into a huge teardrop away from the Sun, deflecting most solar-wind particles
• Van Allen Radiation Belts occur where Earth's magnetic field starts to strengthen, trapping cosmic rays and solar-wind particles that managed to enter the magnetosphere
• Particles passing through the Van Allen Belt reach Earth and follow magnetic lines to the poles causing gases to glow as aurorae

  
• Latitude


  East-west lines parallel to the equator
• Longitude


  North-south lines connecting poles

  
• Atmosphere


  The gaseous layer enveloping the whole Earth, containing a mixture of gases known as air
• Composition of air


  • 78% nitrogen (N2)
  • 21% oxygen (O2)
  • 1% minor gases (argon, carbon dioxide, neon, methane, ozone, carbon monoxide, sulphur dioxide)
• Variable amounts of water (H2O) vapour are prominent at lower elevations that form clouds, hiding about 70% of the planet's surface
• Density and pressure of the atmosphere

  Progressively increase towards Earth's surface due to the weight of overlying air
• 99% of atmospheric gas lies at lower 50 km of atmosphere; above, pressure and density are very low
• Beyond 600 km, molecules no longer interact and collide like a gas; considered upper boundary of atmosphere
• Layers of the atmosphere

  • Thermosphere
  • Mesosphere
  • Stratosphere
  • Troposphere
• Components of the Earth System

  • Atmosphere
  • Hydrosphere
  • Cryosphere
  • Biosphere
  • Solid Earth
• Habitable zone


  Distance from Sun with temperatures between boiling and freezing points of water
• Mars and Venus do not have life mostly due to the abilities of their atmospheres to trap heat
• The Earth's System is dynamic and constantly moving, requiring significant energy from heat from inside the Earth, gravity, Sun's heat, and Sun's light
• Earth's surface composition


  • 30% dry land (continents and islands)
  • 70% surface water (saline oceanic water, some fresh surface and shallow groundwater)
  • Ice covers land and sea
• Surface has topography, i.e. variations in elevation identifying plains, mountains and valleys
• Ocean floor features


  • Abyssal plains
  • Mid-ocean ridges
  • Deep-sea trenches
• Hypsometric curve shows most of land surface is within 1 km of sea level, and most of seafloor lies between 4 km and 5 km of sea level
• Elements making up 91.2% of Earth's mass

  • Iron (35%)
  • Oxygen (30%)
  • Silicon (15%)
  • Magnesium (13%)
• Earth materials


  • Organic chemicals
  • Minerals
  • Glass
  • Melts
  • Rocks
• Types of rocks


  • Igneous
  • Sedimentary
  • Metamorphic
• Other Earth materials


  • Grains
  • Sediment
  • Metals
• Three groups of rocks

  • Igneous rock
  • Sedimentary rock
  • Metamorphic rock