1. The Atmosphere: Our Protective Blanket
The Earth is surrounded by a thick layer of air called the atmosphere. We cannot survive without this air, as it provides the oxygen we breathe and protects us from the harsh conditions of space.
2. What is Air Made Of? (Composition of the Atmosphere)
Air is not a single gas but a mixture of many gases.
- ✓Nitrogen (N₂ - 78%): The most plentiful gas. Plants need it to grow, and they absorb it through the soil.
- ✓Oxygen (O₂ - 21%): The "life-supporting gas" that all humans and animals need for breathing (respiration). Plants produce oxygen during photosynthesis.
- ✓Carbon Dioxide (CO₂ - 0.03%):
- Plants use it to make food (photosynthesis).
- It absorbs heat from the sun, which helps to keep the Earth warm.
- However, an increase in CO₂ (from burning fuels) traps too much heat, leading to Global Warming.
- ✓Other Components (0.17%): This includes small amounts of gases like argon and helium, as well as water vapour and dust particles. Dust particles are important because they help water vapour condense to form clouds.
3. Layers of the Atmosphere
The atmosphere is divided into different layers based on temperature. From the ground up, they are:
- ✓Troposphere (0-13 km):
- The densest layer and the one we live in.
- All weather phenomena (clouds, rain, wind) happen here.
- Temperature decreases as we go higher (this is called the Normal Lapse Rate).
- ✓Stratosphere (13-50 km):
- A calm and clear layer with no clouds, making it ideal for aeroplanes to fly in.
- Contains the very important Ozone Layer. This layer acts as a shield, protecting us from the sun's harmful ultraviolet (UV) rays.
- ✓Mesosphere (50-80 km):
- A very cold layer.
- Meteors (shooting stars) burn up in this layer upon entering the atmosphere.
- ✓Thermosphere (80-400 km and beyond):
- The air is very thin here.
- Contains a sub-layer called the Ionosphere, which has electrically charged particles (ions).
- These ions reflect radio waves back to Earth, which makes long-distance wireless communication possible.
4. Atmospheric Temperature and Pressure
- ✓Atmospheric Pressure: This is the pressure or weight of the air pushing down on the Earth's surface.
- It is measured with an instrument called a barometer.
- The unit of measurement is millibar (mb).
- Air pressure is highest at sea level and decreases as we go higher up in the mountains.
- ✓Interesting Fact: Higher temperature means lower air pressure, and lower temperature means higher air pressure.
5. Wind: Moving Air
Wind is simply the movement of air from an area of high pressure to an area of low pressure.
How it works:
- ✓When an area gets hot, the air above it rises, creating a low-pressure zone.
- ✓Cooler, denser air from a nearby high-pressure zone rushes in to fill the space. This movement is what we feel as wind.
Monsoons are seasonal winds that are crucial for India's agriculture.
6. Rainfall and the Water Cycle
Rain is essential for all life on Earth. Its formation is part of the water cycle.
Mechanism of Rainfall:
- ✓Evaporation: The sun heats water from oceans and lakes, turning it into water vapour which rises.
- ✓Condensation: As the warm, moist air rises, it cools down. The water vapour condenses into tiny water droplets, forming clouds.
- ✓Precipitation: When these droplets become too heavy, they fall to the Earth as rain, snow, or sleet.
Measuring Rainfall: An instrument called a rain gauge is used to measure rainfall.
Effects of Rainfall:
- ✓Scarcity: Too little rain leads to drought.
- ✓Excess: Too much rain causes floods.
7. Weather vs. Climate
It's important to know the difference between these two terms.
- ✓Weather: Describes the state of the atmosphere (temperature, humidity, rainfall) for a short period (like a day or a week) in a specific place. For example, "It is sunny in Jamshedpur today."
- ✓Climate: Describes the average weather conditions of a large area over a long period (like 30 years or more). For example, "The climate of India is monsoonal."
8. Air Pollution
When harmful substances (gases, dust, smoke) mix with the air, it becomes polluted.
- ✓Causes: Smoke from vehicles, factories, and burning of farm waste.
- ✓Smog: A dangerous mixture of smoke and fog that causes health problems.
- ✓Pollution adds to global warming and damages our environment.
9. Keywords to Remember
- ✓Global Warming: A gradual increase in the overall temperature of the Earth's atmosphere.
- ✓Humidity: The amount of water vapour in the atmosphere.
- ✓Monsoons: Seasonal reversal of the wind direction according to the change in season.
- ✓Photosynthesis: The process by which plants use sunlight, water, and carbon dioxide to create their food and release oxygen.