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, N 2 (78%) Oxygen, O 2 (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 Pressure

Pressure 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 Mercury 76 cm of Mercury 1013 millibars (mb)

Aneroid Barometer - also altimeter Average Sea Level Atmospheric Pressure: 29.92” of Mercury 76 cm of Mercury 1013 millibars (mb)

Atmospheric Pressure Is Related to Weather Conditions Less-Dense, Low Pressure Rises: Clouds and Stormy Weather More-Dense, High Pressure Air Sinks: Fair Weather

The Vertical Thermal Structure of the Atmosphere OZONOSPHERE IONOSPHERE

Temperature, Precipitation, and Elevation Temperature decreases with increasing elevation. Precipitation increases with increasing elevation.

Temperature Inversions When 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] mesospher e

Aurora borealis / australis The northern / southern lights (click for video)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 (N 2 ) 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 (O 3 ) absorbs UV rays The Importance of Stratospheric Ozone O 2  2 O then O + O 2  O 3  light O 3  O 2 + 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 O 3 –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 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