Structure of the Earth – Quick-Review Notes

Branches of Earth Science

• Geology – Earth’s structure, formation, forces; founded by James Hutton

• Geography – spatial relationships between people & environment; Eratosthenes

• Physiography – physical surface features & natural processes; Alexander von Humboldt

• Geophysics – Earth’s shape & physical reactions to forces; Alfred Wegener

• Soil Science – outermost layer & soils; Vasily Dokuchaev

• Hydrology – water distribution & movement; Robert E. Horton

• Oceanography – all ocean aspects; Matthew F. Maury

• Glaciology – cryosphere & environmental impact; Louis Agassiz

• Atmospheric Science – entire atmosphere; Wladimir Köppen

• Meteorology – troposphere & lower stratosphere phenomena; Luke Howard

• Biology – living organisms; Aristotle
  

  • Zoology – animals
  

  • Botany – plants (Theophrastus)

Earth’s History

• Age
  $\approx4.5\,\text{billion years}$

• Formation: planetary disc → proto-planets (ice & rock, no atm/water)

• Core differentiation: solid inner core, liquid outer core

• Theia impact → Moon; early land masses form

• Atmosphere from volcanic outgassing; gravity retains gases

• Oceans from cometary ice / moisture

• Principle of Uniformitarianism – present processes
  $\approx$ past processes

• Supercontinents timeline:
  

  Vaalbara (3.6 billion years ago)

  Ur (3.1 billion years ago)

  Kenorland  (2.6 billion years ago)

  Columbia/Luna (1.8 Billion years ago)

  Rodinia (1.1 years ago)

  Pannotia (600-540 million years ago)

  Pangaea (300 years ago)

• 
  Ancient ocean:
  $\text{Panthalassa}$

Earth’s Subsystems

Atmosphere (altitude & typical temperature ranges)

• Troposphere
  $0–20\,\text{km}$
  :
  $15^{\circ}\text{C}\to-51^{\circ}\text{C}$

• Stratosphere
  $20–50\,\text{km}$
  (Ozone layer) :
  $-51^{\circ}\text{C}\to-2.5^{\circ}\text{C}$

• Mesosphere
  $50–90\,\text{km}$
  :
  $-2.5^{\circ}\text{C}\to-147^{\circ}\text{C}$

• Thermosphere
  $90–800\,\text{km}$
  :
  $-85^{\circ}\text{C}\to2000^{\circ}\text{C}$

• Exosphere

  800-10,000km
  :
  200Celius

Geosphere

• Crust : solid silicate rocks (basalt, granite); thickness
  5-50km
  
  

  • Boundary: Mohorovičić (Moho) discontinuity

• Mantle :

  2900km
  thick; Fe, Mg, Al, O
  

  • Asthenosphere (flowing); convection currents
  

  • Mantle Transition Zone
  

  • Gutenberg discontinuity (mantle–outer core)

• Core :
  

  • Outer core

  2100km

  approx2100\,\text{km

• , liquid Fe–Ni (creates magnetic field)
  

  • Inner core
  1200km
  , solid Fe–Ni;
  $\sim5500^{\circ}\text{C}$
  
  

  • Lehmann discontinuity (outer–inner core)

Hydrosphere

• Global water:

  97.5$
  saline

  2.5$
  fresh
  

  • Glaciers
  1.7%
  (of total), consumable fresh water

  0.77

• Water cycle: evaporation, condensation, precipitation, runoff, infiltration, transpiration, subduction release (volcanic steam)

Biosphere (Cycles)

• Oxygen cycle: produced mainly by photosynthesis (land plants & phytoplankton); consumed by respiration, decomposition, oxidation

• Carbon cycle: photosynthesis
  $\leftrightarrow$
  respiration, decomposition; fossil fuel storage & human extraction; ocean–atmosphere diffusion; sedimentation

• Nitrogen cycle:
  

  • Nitrogen fixation (
  by bacteria/lightning
  

  • Ammonification, nitrification (
  returns gas to atmosphere

Geomorphic Processes

• Endogenic forces (internal): driven by isostasy & mantle convection
  

  • Diastrophism – slow bending, folding, faulting
  

  • Fast movements – earthquakes, volcanic eruptions

• Exogenic forces (external): weathering, erosion, mass movement; lower & fill Earth’s surface

Crustal Deformation

Epeirogenic (continent-scale)

• Uplift → raised beaches, elevated terraces & sea caves

• Subsidence → sinking crust, subduction zones

• Plutonism – intrusive magma forms plutons

• Volcanism – extrusive magma builds volcanic rocks

Orogenic (mountain-building)

Folding (compression)

• Monocline – single gentle bend

• Anticline – convex-up arch

• Syncline – concave-up trough

• Overturned – limbs tilt past vertical

• Recumbent – fold on its side

Faulting (fracturing & displacement)

• Normal – hanging wall down (tension)

• Reverse – hanging wall up (compression)

• Thrust – low-angle reverse

• Strike-slip (lateral)

• Oblique-slip – combined dip & strike movement

• Horst – uplifted block between faults

• Graben – down-dropped block between faults