Composition and Structure of the Atmosphere — Syllabus
ICSE · Class 9 · Geography
What Composition and Structure of the Atmosphere covers in ICSE Class 9 Geography: 4 topics, for the 2026-27 session.
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Topics in Composition and Structure of the Atmosphere
1. Composition of the Atmosphere
- Nitrogen and oxygen are the two main gases in clean dry air.
- Nitrogen makes up 78% of the atmosphere and oxygen makes up 21%.
- Together, nitrogen and oxygen make up about 99% of clean dry air.
2. Structure of the Atmosphere
- On the basis of structure, the atmosphere has four main layers: troposphere, stratosphere, ionosphere, and exosphere.
- Troposphere is the lowermost layer where we live.
- Almost all weather phenomena take place in the troposphere.
3. Ozone in the Stratosphere
- Ozone is made of three oxygen atoms, while ordinary oxygen has two atoms.
- Ozone forms in the upper stratosphere when ultraviolet radiation breaks an oxygen molecule into atoms that combine to form ozone.
- Ozone absorbs harmful ultraviolet radiation from the Sun.
4. Greenhouse Effect and Global Warming
- Almost all the energy available to the Earth and its atmosphere comes from the Sun.
- Direct ultraviolet rays of the Sun are extremely harmful for living beings.
- Greenhouse gases include carbon dioxide, methane, nitrous oxide, and water vapour.
Key Concepts
Central concept: Atmosphere: composition, structure, ozone layer, and global warming
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Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.
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