6.1A Atmosphere Notes

1. The atmosphere is a multilayered, dynamic envelope of gases, liquids, and suspended solids that surrounds Earth.
2. It forms the outer limit of the biosphere, acting as a protective barrier that separates Earth from outer space.
3. Its composition, structure, and physical processes make life possible by regulating temperature, filtering radiation, enabling weather, and redistributing energy and gases across the planet.
4. The atmosphere interacts continuously with the lithosphere, hydrosphere, and biosphere, creating interconnected Earth system processes.

Composition of the Atmosphere

1. The atmosphere contains a relatively stable mixture of gases up to about 80 km above Earth’s surface.
2. These gases are vital for climate regulation, respiration, and ecological balance.

Trace Gases (<0.1%)

1. Carbon dioxide (CO₂) (~0.04%): vital for photosynthesis and regulating Earth’s temperature through the greenhouse effect.
2. Water vapour (H₂O): influences weather, cloud formation, and precipitation.
3. Ozone (O₃): concentrated in the stratosphere; absorbs harmful UV radiation.
4. Methane (CH₄) & Nitrous oxide (N₂O): potent greenhouse gases affecting climate dynamics.

Suspended particles

1. Dust
2. Ash
3. Soot
4. Sea salt
5. Aerosols

Structure of the Atmosphere

The atmosphere is divided into distinct layers based on temperature variations.

Troposphere (0–12 km)

1. The troposphere is the lowest atmospheric layer, where almost all weather processes occur.
2. Air temperature decreases with increasing altitude.
3. This layer contains most of the atmosphere’s water vapour and greenhouse gases.
4. Human activities, including pollution and fossil fuel combustion, primarily affect this layer.

2. Stratosphere (12–50 km)

1. The stratosphere contains the ozone layer, which absorbs most of the harmful ultraviolet radiation from the Sun.
2. Unlike the troposphere, temperature increases with altitude due to ozone absorbing solar radiation.
3. This layer is relatively stable and experiences limited vertical mixing.

3. Mesosphere (50–80 km)

1. The mesosphere is the coldest atmospheric layer.
2. Meteors burn up in this layer due to increasing atmospheric friction.

4. Thermosphere (80–700 km)

1. The thermosphere has very low gas density but extremely high temperatures because the few particles present absorb large amounts of solar radiation.
2. Auroras appear in this layer, and satellites and space stations orbit within it.