Geography - Earth, Environment & Resources • Topic 2 of 4

Air, Water & Natural Environment

The atmosphere is the blanket of air that surrounds the Earth, held in place by gravity. It is made up mostly of nitrogen (about 78%) and oxygen (about 21%), with the remaining 1% being carbon dioxide, argon and other gases plus water vapour and dust. The atmosphere has five layers, from the ground upward: the troposphere (where all weather happens), the stratosphere (which contains the protective ozone layer), the mesosphere, the thermosphere (where the ionosphere helps radio communication), and the exosphere. Students must distinguish weather from climate: weather is the day-to-day condition of the atmosphere of a place (today is hot and sunny), while climate is the average weather of a place taken over a long period of time, usually 25 years or more. The hydrosphere is the water domain. About 71% of the Earth's surface is covered by water, and roughly 97% of all water is the salty water of the oceans - only a small fraction is fresh water. The water cycle is the continuous movement of water through evaporation (water turning to vapour by the Sun's heat), condensation (vapour cooling into clouds), precipitation (rain, snow) and collection back in oceans and rivers - the same water circulating endlessly. The major oceans are the Pacific (the largest and deepest), Atlantic, Indian, Southern and Arctic. On land, the lithosphere shows the major landforms: mountains (very high land with steep slopes, like the Himalayas), plateaus (elevated flat-topped land, like the Deccan Plateau), and plains (low, flat and fertile land formed often by rivers, like the Indo-Gangetic plains, which support dense populations and agriculture).

✅ Solved examples

1. Name the two most abundant gases in the atmosphere and their approximate proportions.
Nitrogen (about 78%) and oxygen (about 21%). Together they make up about 99% of the air; the remaining 1% includes carbon dioxide, argon and other gases.
2. What is the key difference between weather and climate?
Weather is the day-to-day condition of the atmosphere of a place (hot, rainy, windy today). Climate is the average of weather conditions taken over a long period, usually 25 years or more.
3. In the water cycle, the process by which water vapour cools and turns into tiny droplets forming clouds is called:
Condensation. The full cycle is evaporation -> condensation -> precipitation -> collection, repeating continuously.
4. Which is the lowest layer of the atmosphere, and why is it important?
The troposphere. It is the layer closest to the Earth where we live and breathe, and it is where all weather phenomena (clouds, rain, storms) occur.

✏️ Practice — try these, take hints as needed

1. The protective ozone layer that absorbs harmful ultraviolet rays is found in which atmospheric layer?
Just above the troposphere.
Aeroplanes fly in its lower part.
Stratosphere
2. Approximately what percentage of the Earth's surface is covered by water?
Most of the planet.
A little over two-thirds.
About 71%
3. Which is the largest and deepest ocean on the Earth?
Surrounds many Asian and American coasts.
Its name suggests calmness.
Pacific Ocean
4. Elevated flat-topped landforms with steep sides, such as the Deccan, are called:
Higher than plains, flatter than mountains.
Often called the table land.
Plateaus

📝 Topic test — 8 questions

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