GEO 130 - Earth's Atmosphere

Three ways Earth's atmosphere maintains habitability

Supplies gases essential for life, filters harmful rays and shields against meteors, and maintains favorable temperature via the greenhouse effect while redistributing energy/moisture

What binds and protects Earth's atmosphere?

Gravity holds it in place; the magnetosphere (Earth's magnetic field) shields it from solar winds

Two categories of atmospheric gases

Permanent (constant/static) gases and trace (variable/dynamic) gases

The three permanent gases and their proportions

Nitrogen (78%), Oxygen (21%), Argon (0.9%)

Why are permanent gas proportions relatively constant?

Large volume and stable biogeochemical cycles

Six important variable (trace) gases

CO2, H2O, N2O, CH4, O3, and CFCs

Why do variable gas proportions fluctuate?

Small base concentrations and variable sources and sinks

What do variable gases have in common?

They are greenhouse gases, and human activity modifies their concentrations

Two cycles important for the biosphere and energy balance

The carbon cycle and the water cycle

Effect of increasing variable gases in the atmosphere

Global warming

Particulate matter / air pollution

An important part of atmospheric function; anthropogenic and excess amounts constitute air pollution

Atmospheric profile

A vertical cross-section (side view) of the atmosphere used to study its structure

Three angles used to study atmospheric structure

Temperature, Composition, and Function

Four temperature-based layers of the atmosphere (in order from surface)

Troposphere, Stratosphere, Mesosphere, Thermosphere

Troposphere

Temperature decreases with altitude; contains the biosphere and most weather events

Stratosphere

Temperature increases with altitude; contains the ozone layer

Mesosphere

Temperature decreases with altitude; where most meteors burn up and noctilucent clouds form

Noctilucent clouds

The highest clouds, formed mainly of water ice plus other debris material, found in the mesosphere

Thermosphere

Temperature increases with altitude to very high levels; where auroras occur and gamma/X-rays are filtered out (the ionosphere)

Two composition-based divisions of the atmosphere

The heterosphere and the homosphere

Heterosphere

Composed of unblended layers of gases by atomic weight (~80/100-480 km altitude, 0.001% of atmospheric mass)

Homosphere

Homogeneous in its major components (Oxygen, Nitrogen, Argon), with exceptions of other gases

Three function-based divisions of the atmosphere

The ionosphere, the ozonosphere, and the magnetosphere

Ionosphere

Filters out most harmful incoming solar radiation and charged particles

Ozonosphere (ozone layer)

Filters out harmful ultraviolet radiation

Montreal Protocol (1987)

International treaty that addressed the ozone depletion problem; the ozone hole still remains over Antarctica

Magnetosphere

Earth's magnetic field, generated by Earth's rotation (with the inner core rotating at a different speed); deflects solar winds toward the poles, producing auroras