Layers of the Earth

1
Layers of the Earth

• The Earth consists of many layers, both within
  and around it.
• The layers of the Earth are
• Crust thin hard outer layer of the Earth.
  Between 3 25 miles thick.
• Mantle Thick layer of molten material just
  beneath the crust 1800 miles thick (1600 4000
  oF).
• Outer core hot (4000 - 9000 oF) liquid metal
  (primarily nickel and iron) layer 1800 miles
  beneath the crust and about 1400 miles thick
• Inner core hot (9000 oF) solid metal center
  about 4000 miles beneath the crust and about 800
  miles thick

2

• Everything we deal with on the Earth comes from
  the region called the lithosphere which is
  composed of the crust and the upper portion of
  the mantle.
• Convection currents of the molten material within
  the mantle moves the crust. Leading us to the
  Theory of Plate Tectonics
• Convection in the outer core, combined with
  stirring caused by the Earth's rotation gives
  rise to Earths magnetic field.
• Seismic experiments proved the inner core is
  solid rather than liquid.

3
The Atmosphere

• Earths atmosphere begins at the surface of the
  Earth and extends upwards for hundreds of
  kilometers.
• The atmosphere is divided into 5 regions
• Troposphere (0 15 km)
• Stratosphere (15 50 km)
• Mesosphere (50 80 km)
• Thermosphere (80 500 km)
• Exosphere (500 km)

4
The Troposphere

• The troposphere extends from the surface of the
  crust and upwards to about 15 km.
• As altitude increases, temperature generally
  decreases, reaching about -58oC at 12 km.
• In this region we see weather phenomena such as
  rain, snow, and wind.
• The composition of air in the troposphere is
  about
• 78 N2 20.9 O2
• 0.93 Ar 0.033 CO2
• 0.00182 Ne 0.00052 He
• other trace compounds include methane, krypton,
  hydrogen, nitrous oxide, and xenon

5
Chemistry of the Troposphere

• Composition of the troposphere varies from area
  to area. Human activity causes problems.
• Photochemical smog
• through burning of fossil fuels, nitrogen reacts
  with oxygen to form nitrogen oxides such as NO
  and NO2
• N2(g) O2(g) ? 2NO(g)
• 2NO(g) O2(g) ? 2NO2(g)
• NO2 is broken down by UV radiation to create
  ozone (O3)
• NO2(g) UV radiation ? NO(g) O(g)
• O(g) O2(g) ? O3(g)

6

• Acid Rain
• High concentrations of sulfur trioxide (SO3) gets
  into the atmosphere through the burning of coal
  and oil. This then reacts with water in the
  atmosphere to form sulfuric acid (H2SO4)
• SO3(g) H2O(l) ? H2SO4(aq)
• This also happens with nitrogen oxides to form
  nitric acid
• NO2 (g) H2O(l) ? HNO3(aq)
• Acid rain increases acidity in soil, removing
  available nutrients for plants
• It also increases acidity in streams, rivers,
  lakes, etc. potentially harming aquatic life.
• Additionally, it can corrode surfaces

7
The Stratosphere

• Begins 15km above the Earths surface and extends
  upwards to about 50km.
• Temperature ranges from -58oC to -3oC
• Chemistry of the stratosphere focuses around
  ozone reactions
• 80-90 of Earths ozone is located in the ozone
  layer. This layer of ozone helps protect the
  Earth from potentially harmful UV radiation from
  the sun.

8

• O2 in the stratosphere absorbs UV energy through
  a process called photodissociation by the
  following reaction
• O2 UV ? O O
• Ozone then forms
• O O2 ? O3
• Newly formed ozone also absorbs UV
• O3 UV ? O O2
• The reaction can now begin again and repeat in a
  cycle. This is known as the ozone-oxygen cycle

9
CFCs and the Ozone Layer

• Compounds called chlorofluorocarbons (CFCs),
  invented in the 1930s were used extensively in
  everyday life as refrigerants in refrigerators
  and air conditioners and as propellants in spray
  cans.
• In 1971, it was discovered that these CFCs when
  released into the atmosphere didnt simply just
  go away and were building up in the upper
  atmosphere.
• In 1974 F.Sherwood Rowland and Mario Molina
  proposed that CFCs in the stratosphere would
  interrupt the ozone-oxygen cycle.

10

• CFCs interact with UV radiation
• CF2Cl2 UV ? CF2Cl Cl
• Chlorine atom interacts with ozone
• Cl O3 ? ClO O2
• ClO combines with free oxygen atoms
• ClO O ? Cl O2
• Cl atoms are free to again react with O3, so
  function as a catalyst in depleting ozone in the
  upper atmosphere giving a net reaction of
• O3 O ? 2O2
• Each Cl atom remains in the stratosphere for
  about 2 years before it is destroyed in other
  reactions. It is capable of breaking down about
  100,000 molecules of ozone