CBSE Class 9 Science Chapter 13 Earth as a system: Energy, Matter and Life Notes
Preparing for exams becomes easier when students can revise concepts quickly and understand each topic clearly. CBSE Class 9 Science Notes provide concise explanations, important points, and syllabus-based information that help students strengthen their basics, remember key ideas, and revise effectively. Chapter 13, “Earth as a System: Energy, Matter and Life,” explains how different parts of Earth interact to support life. It covers the flow of energy from the Sun, the movement of matter through natural cycles, and the relationship between living organisms and their environment. Students learn how Earth works as a connected system and why environmental balance is important for life.
1.0Download CBSE Notes in Class 9 Science Earth as a system: Energy,Matter and Life
CBSE Notes for Class 9 Science Chapter 13 Earth as a System: Energy, Matter and Life are created to make the concepts simple, enhance the understanding and help in rapid revision.
2.0Important Concepts of Class 9 Science Chapter 13 Earth as a system: Energy,Matter and Life
Earth's Five Interconnected Spheres
Earth is the only known planet where all five spheres actively interact to support life.
Solar Radiation & Electromagnetic Spectrum
- Sun's energy reaches Earth in the form of electromagnetic (EM) waves.
- EM waves are non-mechanical waves, so they do not require a material medium to travel.
- They travel at a speed of 3 × 10⁸ m/s in a vacuum.
- The electromagnetic spectrum, arranged from lowest to highest energy, is:
- Radio waves
- Microwaves
- Infrared (IR)
- Visible light
- Ultraviolet (UV)
- X-rays
- Gamma rays
- About 99% of the Sun's energy reaching Earth lies in the ultraviolet (UV), visible, and infrared (IR) regions of the spectrum.
- The Earth's atmosphere filters out most harmful high-energy radiation:
- Gamma rays and X-rays are almost completely absorbed by the atmosphere.
- The ozone layer blocks most of the harmful ultraviolet (UV) rays.
- Different parts of solar radiation have different roles:
- Visible light powers photosynthesis in plants.
- Infrared (IR) radiation warms the Earth's surface.
- Some of the Earth's outgoing infrared radiation is trapped by greenhouse gases such as:
- Carbon dioxide (CO₂)
- Methane (CH₄)
- Water vapour (H₂O)
- This trapping of heat is known as the greenhouse effect, which helps keep the Earth warm enough to support life.Solar Insolation & Solar Constant
- Insolation = solar energy reaching Earth's surface.
- Solar constant ≈ 1.4 kW/m² (1400 J/s/m²) at top of atmosphere.
- Max insolation reaching surface on clear day ≈ 1 kW/m² (lower due to atmospheric losses).
Formula: $$E = I \times A \times t$$ (E = Energy in J, I = Intensity in W/m², A = Area in m², t = Time in s)
Filtration of Solar Radiation (energy budget, clear sky)
Albedo
- Albedo = fraction of sunlight reflected by a surface.
- High albedo (light surfaces) → reflect more, stay cool (e.g., snow ~0.8–0.9).
- Low albedo (dark surfaces) → absorb more, heat up (e.g., ocean water ~0.05–0.10).
Urban Heat Island (UHI) Effect
- Cities warmer than rural areas — concrete/asphalt/steel absorb & slowly release heat.
- Rural areas cooler due to vegetation (shade + transpiration).
Uneven Heating by Latitude
- Sunlight strikes equator directly (concentrated) but poles at low angle (spread over larger area) → equator warmer than poles.
Earth's Atmosphere
- Composition: Nitrogen 78%, Oxygen 21%, trace gases (Ar, CO₂, water vapour).
Layers of the Atmosphere
- Ozone layer depletion caused by CFCs → Montreal Protocol (1987) addressed this.
Wind & Ocean Currents (Driven by Uneven Heating)
Winds
- Blow from high pressure → low pressure.
- Deflected by Earth's rotation (don't move in straight lines).
Local Winds
- Valley breeze: day, warm air rises up slope (valley → mountain).
- Mountain breeze: night, cool air sinks down slope (mountain → valley).
Global Wind Belts (Pressure Belts)
Ocean Currents
- Driven by wind friction, temperature, and salinity differences.
- Form circular systems called gyres — clockwise (N. Hemisphere), counter-clockwise (S. Hemisphere).
- Example: North Atlantic Drift keeps NW Europe's ports ice-free.
- Distribute heat globally, moderate climate, transport nutrients/oxygen for marine life.
Biogeochemical Cycles
Cyclic movement of matter between living (biotic) and non-living (abiotic) components of Earth.
Water Cycle
- Key processes: Evaporation → Condensation → Precipitation (+ Transpiration, Runoff).
Carbon Cycle
- Fast cycle (days–years): Photosynthesis (absorbs CO₂) ↔ Respiration/Decomposition (releases CO₂).
- Slow cycle (millions of years): Dead organisms → fossil fuels → combustion releases CO₂.
- Atmospheric CO₂ risen from ~315 ppm (1960) → 420+ ppm (present) — tracked by the Keeling Curve.
Global Carbon Distribution:
Nitrogen Cycle
- Industrial fixation: Haber–Bosch process (converts N₂ → ammonia for fertilisers; supported Green Revolution).
Oxygen Cycle
- O₂ used up by: combustion, respiration, formation of nitrogen oxides.
- O₂ returned only via: photosynthesis (green plants are the major source).
Human Impact on Earth's Systems
- Fossil fuel burning + deforestation → rising CO₂ → global warming, ocean acidification, extreme weather.
- Deforestation → reduced transpiration/rainfall, soil erosion, habitat loss, altered albedo.
- Excess fertiliser use → eutrophication (algal blooms → oxygen depletion in water bodies).
- Urban emissions → smog and ground-level ozone (harmful, unlike protective stratospheric ozone).
Key International Agreements
3.0Detailed CBSE Notes Class 9 Science Earth as a system: Energy,Matter and Life
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4.0 Why CBSE Notes for Class 9 Science Chapter 13 Earth as a system: Energy,Matter and Life
• Helps students understand how Earth’s different systems interact to support life.
• Provides clear explanations of energy flow, matter cycles, and their role in maintaining environmental balance.
• Simplifies concepts related to the atmosphere, hydrosphere, lithosphere, and biosphere.
• Covers important chapter concepts in a structured way for quick revision and better exam preparation.
• Helps students connect scientific concepts with real-world environmental processes.