Earth as a System Energy Matter and Life Class 9 Notes Science Chapter 13

Experts have designed these Class 9 Science Notes and Exploration Chapter 13 Earth as a System Energy Matter and Life Class 9 Notes for effective learning.

Class 9 Science Chapter 13 Earth as a System Energy Matter and Life Notes

Class 9 Science Exploration Chapter 13 Notes

Class 9 Science Chapter 13 Notes – Class 9 Earth as a System Energy Matter and Life Notes

→ Albedo: The fraction of incoming solar radiation reflected by a surface. High albedo surfaces reflect more and stay cooler; low albedo surfaces absorb more and are warmer.

→ Ammoniflcation: The process by which decomposers break down organic matter from dead organisms and return nitrogen compounds like ammonia to the soil.

→ Atmosphere: The air surrounding Earth, held by gravity. Composed mainly of nitrogen (78%) and oxygen (21%), with small amounts of argon, CO₂, water vapour, and other gases.

→ Biogeochemical cycle: The cyclic movement of matter and energy between the biotic and abiotic components of the Earth across its various spheres.

→ Biosphere: All living organisms and their habitats.

→ Cryosphere: The solid water component, ice and snow which includes Himalayan glaciers, Ladakh snow, and polar ice caps.

→ Denitrification: Conversion of nitrates back into nitrogen gas by bacteria like Pseudomonas, completing the nitrogen cycle.

→ Electromagnetic (EM) waves: Waves that carry energy through a vacuum at the speed of light. The EM spectrum ranges from gamma rays and X-rays to infrared and radio waves.

→ Electromagnetic spectrum: The entire range of EM radiation comprising gamma rays, X-rays, UV, visible light, infrared, microwaves, and radio waves.

→ Eutrophication: The excessive growth of algae in water bodies due to overuse of nitrogen- based fertilisers, depleting dissolved oxygen and killing fish and other aquatic life.

→ Geosphere: The solid component of Earth such as rocks, soil and the Earth’s interior.

→ Greenhouse effect: The trapping of outgoing heat by greenhouse gases, keeping Earth warm enough for life. Excess CO₂ from human activities enhances this effect, causing global warming.

→ Gyres: Large circular ocean current patterns which are formed due to Earth’s rotation.

→ Hydrosphere: All liquid water bodies on Earth.

→ Insolation: The amount of Sun’s radiation that reaches Earth’s surface. Responsible for warming the surface and atmosphere.

→ Mountain breeze: A local wind that blows from the cooled mountain slopes down into the warmer valley after sunset.

→ Nitrification: The conversion of ammonia to nitrite by Nitrosomonas and then to nitrate by Nitrobacter.

→ Planetary winds: Large scale winds driven by pressure differences created by uneven heating between the equator and poles having curved path due to earth’s rotation.

→ Solar constant: The average solar energy received per unit time per unit area perpendicular to the Sun’s rays at the top of Earth’s atmosphere.

→ Stratosphere: Atmospheric layer from 12-50 km. Contains the ozone layer, which absorbs UV radiation. Temperature increases with height here.

→ Troposphere: The lowest atmospheric layer (0-12 km). Almost all-weather phenomena occur here.

→ Urban heat island effect: The phenomenon where cities are warmer than surrounding rural areas because buildings, concrete, and asphalt absorb and re-radiate more solar radiation than vegetation.

→ Valley breeze: A local wind that blows from the cooler valley floor up the heated mountain slope during daytime.

Uneven Heating of the Earth

• The Sun is the primary source of energy on Earth, sending energy as electromagnetic (EM) waves at the speed of light (3 × 10⁸ ms^-1).
• The EM spectrum ranges from high-frequency gamma rays and X-rays to low-frequency infrared and radio waves.
• About 99% of the Sun’s energy reaching Earth falls in the UV, visible, and infrared range.

→ Interaction of Solar Radiation on the Earth’s Surface:

• The amount of solar radiation received at the top of the atmosphere is the solar constant ≈ 1.4 kWm^-2 (1400 Js^-1m^-2).
• The radiation reaching Earth’s surface is called insolation; its maximum value under clear skies is ~ 1 KWm^-2
• The fraction of solar radiation reflected by a surface is its albedo. High albedo (Snow, ice) = cooler; low albedo (black soil, ocean) = warmer.

→ Latitude and Earth’s Shape: Earth’s spherical shape causes uneven solar radiation — equatorial regions receive concentrated radiation while polar regions receive spread-out, weaker radiation.

→ Role of the Atmosphere:

• The atmosphere consists of layers namely, Troposphere (0 – 12 km), Stratosphere (12 – 50 km), Mesosphere (50 – 85 km), Thermosphere (85 – 600 km), and Exosphere (600 – 10,000 km).
• Nearly all weather occurs in the troposphere. The ozone layer in the stratosphere absorbs harmful UV radiation.
• Greenhouse gases (CO₂, CH₄, water vapour) trap outgoing infrared radiation, keeping Earth warm enough for life.

Uneven Heating Causes Wind and Ocean Currents

→ Local Winds: Valley breeze (daytime — cool valley air rises up heated slopes) and mountain breeze (night — cooled slope air sinks into valley).

→ Planetary Winds: Large-scale pressure belts created by uneven equatorial and polar heating drive global wind circulation. Earth’s rotation causes these winds to follow curved paths (Coriolis effect) — rightward in Northern Hemisphere, leftward in Southern Hemisphere.

→ Ocean Currents:

• Driven by planetary winds, temperature/salinity differences, Earth’s rotation, and land masses. Form large circular gyres — clockwise in the Northern Hemisphere, counter-clockwise in the Southern Hemisphere.
• Ocean currents regulate Earth’s climate by transporting heat from the equator toward the poles.
  Example: North Atlantic Drift keeps European ports ice-free in winter.

Biogeochemical Cycles

The continuous cycling of matter and energy between living (biotic) and non-living (abiotic) components is called the biogeochemical cycle.

→ Water Cycle:

• Evaporation → condensation → precipitation → runoff → infiltration.
• Climate change intensifies this cycle (heavier rains, droughts, rising sea levels).

→ Carbon Cycle:

• Carbon cycle has a fast cycle (days-years via photosynthesis/respiration) and a slow cycle (millions of years via fossil fuel formation).
• Human activities have raised atmospheric CO₂ ~ 35 % since 1960 (315 → 420 ppm).

→ Nitrogen Cycle:

• Nitrogen fixation (Rhizobium, Azotobacter) → nitrification (Nitrosomonas, Nitrobacter) → assimilation → ammonification → denitrification (Pseudomonas).
• Haber-Bosch process industrially fixes most nitrogen today.

→ Oxygen Cycle:

• O₂ is consumed in respiration and combustion; restored mainly by photosynthesis.
• About 21 % of atmosphere is free oxygen.

Human Impact on Earth’s Processes

• Excess CO₂ makes ocean water more acidic, threatening plankton and coral reefs. Warmer oceans absorb less CO₂, reducing their role as carbon sinks.
• Fertiliser overuse causes eutrophication — algal blooms deplete oxygen and kill aquatic life.
• Deforestation reduces photosynthesis, increases soil erosion, alters albedo, reduces rainfall, and lowers biodiversity.
• Vehicular emissions form ground-level ozone (smog), harming health.
• Global solutions include the Montreal Protocol (ozone recovery), and individual actions like saving energy, planting trees, and reducing waste.