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.

5. Exosphere (Above 700 km)

1. The exosphere gradually fades into outer space.
2. Gas particles are extremely sparse and can escape into space.

Redistribution of Atmospheric Gases

1. Wind

1. Wind is created by differences in air pressure known as the pressure gradient force.
2. Air moves from high-pressure regions to low-pressure regions, and strong pressure differences generate stronger winds.
3. Extreme examples include tropical cyclones, where pressure differences create very high wind speeds.

2. Convection

1. Warm air near the Earth’s surface rises because it expands and becomes less dense.
2. As the air rises, it cools, condenses, and transfers heat upward, forming clouds and storms.
3. Convection is a major driver of weather patterns and vertical mixing.

3. Diffusion

1. Atmospheric gases naturally spread from areas of high concentration to areas of low concentration.
2. This slow but constant process helps maintain a uniform atmospheric composition.

4. Global Circulation Patterns

1. Large-scale systems such as the trade winds, jet streams, and westerlies transport heat, moisture, and gases across continents and oceans.
2. These circulation patterns influence climate zones and seasonal weather.

5. Turbulence

1. Airflow becomes turbulent when it encounters mountains, forests, buildings, or rough terrain.
2. Turbulence enhances mixing and influences weather and pollutant dispersal.

How the Atmosphere Supports Life

1. Temperature Regulation

1. Greenhouse gases trap heat and maintain a stable global temperature that supports life.
2. Without the atmosphere, Earth would experience extreme temperature fluctuations between day and night.

2. Protection from Radiation

1. The ozone layer absorbs harmful ultraviolet radiation.
2. The atmosphere scatters and filters solar radiation, reducing exposure to damaging wavelengths.

3. Gas Availability for Biological Processes

1. Oxygen is available for respiration in animals and many microorganisms.
2. Carbon dioxide is available for photosynthesis in plants and algae.
3. Nitrogen contributes to nutrient cycles that sustain ecosystems.

4. Weather and Water Cycle Regulation

1. The atmosphere enables precipitation, evaporation, cloud formation, and weather patterns.
2. These processes support ecosystems and influence freshwater distribution worldwide.