The Earth’s Atmosphere

What holds the Earth’s atmosphere to the planet?

GRAVITY

Development of the Earth’s Atmosphere

• Primordial atmosphere (4.6 to 4.0 bya)

• Evolutionary atmosphere (4.0 to 3.3 bya)

• The living atmosphere (3.3 bya to 500 mya)

• The modern atmosphere (500 mya to present)

The Modern Atmosphere (500 mya to the present)

• Nitrogen, N2 (78%)

• Oxygen, O2 (21%) 99.9%

• Argon, Ar (0.9%)Trace gases

– water vapor (0-4%)– carbon dioxide (.036%), methane (greenhouse

gases)– nitrogen oxides, sulfur oxides (acid rain and

more)– many other trace gases– particulate (dust)

Atmospheric PressureAtmospheric

Pressure

Atmospheric PressurePressure can be thought of as

the weight of all overlying air (though, in reality, pressure exerts force in all directions).

Mercury Barometer- Invented by Toricelli, 1643

Average Sea Level Atmospheric Pressure:

29.92” of Mercury76 cm of Mercury1013 millibars (mb)

Aneroid Barometer- also altimeter

Average Sea Level Atmospheric Pressure:

29.92” of Mercury76 cm of Mercury1013 millibars (mb)

Atmospheric Pressure Is Related to Weather

ConditionsLess-Dense, Low

Pressure Rises: Clouds and Stormy Weather

More-Dense, High Pressure Air Sinks: Fair Weather

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OZONOSPHERE

IONOSPHERE

Temperature, Precipitation, and ElevationTemperature decreases with increasing elevation.

Precipitation increases with increasing elevation.

Temperature InversionsWhen warmer air overlies cooler air, pollutants and fog are trapped beneath the inversion.

Common Winter Radiation Inversion in Valleys

Temperature Inversions

Common Summer Inversion in Los Angeles

Troposphere[tropopause at 8-18 km, or 5-11 miles]

• Troposphere– contains 90% of the mass

of the atmosphere – decrease of mass with altitude– mostly mixed gases (not

layered)– clouds / weather layer– temperatures decrease with

altitude - WHY?

Stratosphere

– decrease in amount of gases with altitude

– mixed gases (not stratified) except for ozone layer

– temperatures increase with altitude

[stratopause at 50 km, about 30 miles]

[tropopause at 8-18 km, or 5-11 miles]

mesosphere

Aurora borealis / australis• The northern / southern lights

(click for video)• (click for photos and legends)

• Thermosphere and uppermost Mesosphere– solar wind (clouds of electrically charged

particles)– Earth’s magnetic field directs them towards

poles

– excite oxygen (O) and nitrogen (N2) ions in ionosphere emit light

• Ozone forms naturally in stratosphere

• UV radiation (sun) --> mutations– plankton reduced (food chain base), crops

decline– weaker immune systems, skin cancer

• Stratospheric ozone (O3) absorbs UV rays

The Importance of Stratospheric Ozone

O2 2 O then O + O2 O3

light

O3 O2 + O

UV rays

The Importance of Stratospheric Ozone

CFC’s– link to ozone hole established in 1970s– Chloroflourocarbons (refrigerants,

aerosols)– one Cl can decompose more than 100,000

O3

– Montreal Protocol, 1987: U.N. agreement on ban

– up to 10 years for rising CFC gases to reach stratosphere; once in the stratosphere, CFC’s can last up to 50-100 years

RECENT YEARS

RECENT YEARS

Key Points • Development of Earth’s atmosphere– 4 periods

• Vertical structure of the atmosphere– 4 temperature layers– changes in pressure– Aurora borealis / australis– the ozone layer