The Earth has a History, 4.55 billion years old, same as rest of solar system
     Geosphere (solid part), Hydrosphere (liquid part), Atmosphere (gaseous part)
     each of these spheres interacts; gas can be dissolved in liquid, for example.

Classical Subdivisions of Geosphere:  crust----mantle-----core
     total radius about 6400 km = 4000 miles (recall that 1 mile = 1.6 kilometers; 1 km = 0.6 mi)
     Crust: oceanic , 7 km thick (very uniform), continental crust 40 km thick (20-80 km)
     Mantle:  2900 km total, solid not liquid, dominates Earth
     Core:  outer, 2300 km, liquid iron-nickel, inner, 1200 km, solid iron-nickel

Surface of the Earth
     total surface area about 5 x 10⁸ km² = 2 x 10⁸ mi2

     30% continents, average height about 0.6 km =.4 miles, range 0-9 km (shore to mountains)
          continents used to be smaller in past, continents growing in area over last 4.5 billion years

     70% ocean, average depth about 4 km = 2.5 miles, range 0-11 km
          shallower areas over mid-ocean ridges, such as the Mid-Atlantic Ridge
          deeper areas in trenches, such as the Marianas trench (10.8 km = 35,000 ft deep)
          little detailed ocean exploration, only broad reconnaissance, but changing fast
          oceanic crust found at the bottom of main ocean basins

Terrestrial Environments:  physical environments on land
     fresh water:  groundwater, rivers, swamps-marshes-bogs, lakes and playas
     salt water:  uncommon except in arid environments (CA, UT, Middle East, etc.)
     ice caps and sheets, polar deserts, arctic tundra, high mountains
     continental interiors, plains, grasslands, soils, deserts
     tropical and semitropical jungles, temperate rainforests, rocky and sandy coastlines

Hydrosphere:  includes marine water, water temporarily stored as ice, fresh water
     1.35*10⁹ km³ (97%) in oceans, 2.75*10⁷ km³ (2%) in glaciers, 8.3*10⁶ km³ in groundwater
     only 2*10⁵ km³ fresh water is readily available (on surface in rivers and lakes)
         "fresh" water has ions dissolved in it, just less so than in marine waters

Marine Environments: physical environments in seas, oceans, bays, etc.
     brackish water:  estuaries (where rivers meet the sea), mangrove swamps, deltas
     bays-harbors, continental shelf, continental slope, sea floor (abyssal plain), trenches
     barrier islands, reefs, atolls, seamounts, island arcs

Atmosphere:  divided into layers or spheres just like solid earth
     troposphere: nearest Earth, 17 km/11 mi thick, 95% of all gas (N, O₂, Ar, CO₂, H₂O)
          gases from belching volcanoes, biota, ocean-atmosphere interaction, rotting rocks....
     stratosphere: 17-50 km, includes ozone (O₃) rich layer at bottom ("good ozone")
     mesosphere: 50-80 km, practically empty, does absorb some heat.

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