EVS Chapter 4

How was the current atmosphere created?
H2O Photolysis and Photosynthesis
Carbon Cycle
Carbon is exchanged between biosphere, geosphere, hydrosphere and atmosphere of the Earth.
El Nino
Warm water current that flows periodically southwards along coast of Ecuador and Peru. 
Replaces usually cold northwards-flowing current.
Occurs every 5-7 years, around Xmas. 
Opposite = El Nina
Atmospheric Composition

78% Nitrogen 

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21% Oxygen 

1% CO2 and other gases

Pre-oxygenation: Why was evolution more or less confined to oceans?

Absence of ozone layer.

Water offered protection against UV radiation. 

Portion of incident solar energy that is reflected by a surface. (Globally – 30% is reflected)
High-pressure system
Air moves away from a center of high pressure as it descends. Brings fair weather
Low-pressure system
Air moves towards low-pressure at center of the system and spirals upwards. Brings clouds and precipitation
Thermal Inversion
Layer of cool air occurs beneath a layer of warmer air
Inversion Layer
Band of air in which temperature rises with altitude 
Stratosphere vs. Troposphere (Atmospheric Temperature)

S : Temperature increases with altitude 


T: Temperature decreases with altitude 


Solar radiation (light) can break down chemical bonds.

Example: Atmospheric ozone (O3) breaking down to O2 is a result of photodissociation. 

Controls on deep ocean circulation (vertical mixing)

  1. Temperature and Salinity (density)
  2. Coriolis Force
  3. Position of continents 
  4. Upwelling zones 

Montreal Protocol (1987)

Reduce and eventually eliminate production of CFCs: accelerate development of alternative chemicals


(Production and emissions controlled)  


Very small solid particles suspended in the atmosphere. 


Common examples: sulfates, nitrates, mineral dust, soot, black carbon, etc. 


Originate mostly from combustion 

When is Ozone essential for life on land?
When in Stratosphere 
CLAW Hypothesis

Phytoplankton (biotic source) in oceans produce sulfate gases, which are converted to sulfate aerosols. 

Increased albedo. 


Negative Feedback Loop: aids in stabilizing atmospheric temperature 

Conditions for smog

1. Large number of gas vehicles

2. Heat and sunlight 

3. Limited air mass movement