CBSE Class 8 > Class 8 Notes > Science Curiosity - New NCERT > Cheat Sheet: Earth A Unique Life Sustaining Planet
Cheat Sheet: Earth A Unique Life Sustaining Planet
1. Earth as a Life-Sustaining Planet
1.1 Key observations and imagery
| Term | Definition |
|---|---|
| Unique for life | Only known planet with life in many forms |
| ISRO Earth Observation Satellite | Satellite used to study Earth's special life-sustaining features |
| Image mosaic | Composite formed by combining nearly 3,000 smaller images |
| False-colour image | Image using special colours to highlight land, water, plant growth and environmental changes |
| Blue Planet | Over 70% of Earth's surface is covered with water |
| Crust | Very thin surface layer where most living things exist |
| Other Earth layers | Upper mantle, lower mantle, outer core, inner core |
| Life distribution | Life is mostly restricted to the crust and near-surface parts of the mantle and atmosphere |
1.2 Planets of the Solar System
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
| Term | Definition |
|---|---|
| Terrestrial planets | Mercury, Venus, Earth, Mars; smaller and rocky |
| Gas and ice giants | Jupiter, Saturn, Uranus, Neptune; larger and mostly made of gases and ices |
1.3 Why Venus is the hottest planet
- Venus is not closest to the Sun and is the hottest planet
- Venus's atmosphere is very thick and mainly carbon dioxide (CO2)
- Thick CO2 atmosphere causes Venus to retain large amounts of heat
1.4 Planetary observations
- All planets receive energy from the Sun
- Planets closer to the Sun are generally hotter; those further away are colder
2. Factors that Make Earth Suitable for Life
2.1 Position - Habitable Zone
| Term | Definition |
|---|---|
| Habitable zone (Goldilocks zone) | Region around a star where liquid water can exist |
| Earth's distance from the Sun | Distance that keeps temperatures such that water mostly exists as a liquid |
2.2 Size, atmosphere and related features
| Term | Definition |
|---|---|
| Size and gravity - smaller | Smaller planets may have gravity too weak to hold a dense atmosphere |
| Size and gravity - much larger | Much larger planets may have gravity that makes conditions unsuitable for life as we know it |
| Atmosphere functions | Supplies oxygen for breathing and carbon dioxide for plants |
| Ozone layer | Ozone in the upper atmosphere shields life from harmful ultraviolet (UV) radiation |
| Greenhouse effect | Gases in the atmosphere trap infrared radiation emitted from the surface |
2.3 Mars exploration
| Term | Definition |
|---|---|
| Mangalyaan (Mars Orbiter Mission) | Launched by ISRO in 2013 |
| Mission purpose | Studied Mars' atmosphere and surface and searched for signs of past water |
| Mission significance | Demonstrated how effective, low-cost space missions can deliver valuable scientific results |
2.4 Magnetic field
| Term | Definition |
|---|---|
| Magnetic field | Region around a magnet where its influence is felt; Earth behaves like a giant magnet |
| Generation of Earth's magnetic field | Motion of molten iron in the Earth's outer core generates the magnetic field |
| Space particle hazards | Cosmic rays and solar wind can damage the atmosphere, reduce the ozone layer and harm living organisms |
| Magnetic shielding | The magnetic field deflects many charged particles, protecting the atmosphere |
3. Interactions Between Living and Non-living Components
3.1 Major spheres and roles
| Term | Definition |
|---|---|
| Hydrosphere | Oceans, seas, rivers, lakes and groundwater |
| Hydrosphere functions | Dissolves and transports nutrients |
| Hydrosphere roles for organisms | Helps animals regulate body temperature and digestion |
| Hydrosphere and life processes | Essential for photosynthesis and all cellular processes |
| Freshwater | Required for agriculture and human consumption |
| Hydrological cycle | Water vapour forms clouds that produce rain and snow |
| Atmosphere | Provides air movement (wind) that shapes weather and rainfall patterns |
| Geosphere | Earth's crust containing rocks, soil and minerals that support life |
| Soil | Medium for plant growth containing nutrients released by weathering and decomposition |
| Minerals | Resources such as salt, coal, oil, iron and copper essential for human life and technology |
| Geodiversity | Variety of landforms, rocks and soils that creates different habitats and supports biodiversity |
| Biosphere | Zone where life exists including land, water and the lower atmosphere |
| Plants | Perform photosynthesis using sunlight, water and carbon dioxide to make food and release oxygen |
| Animals | Depend on plants and other animals for food and energy |
| Microorganisms | Decomposers that break down dead matter and recycle nutrients into the soil |
| Ecological interactions | Interactions form complex food chains and food webs that maintain ecological balance (ecology) |
3.2 Balance and reproduction
| Term | Definition |
|---|---|
| Balance of Earth systems | Land, air, water and living organisms interact constantly |
| Reproduction | Biological process by which organisms produce new individuals of the same kind |
| Genes | Instructions passed by parents that determine form and functioning of organisms |
| Variation | Small changes in genes that allow adaptation to changing environments |
| Types of reproduction | Asexual reproduction and sexual reproduction |
| Asexual reproduction | New individuals arise from a single parent and are genetically almost identical to it |
| Sexual reproduction | Two parents contribute genetic material producing offspring with mixed traits |
| Gametes | Male gametes and female gametes carry half the genetic information of each parent |
| Male gametes | Sperm in animals; pollen in flowering plants |
| Female gametes | Egg in animals; ovule in plants |
| Zygote | Formed when male and female gamete fuse and contains a full set of genes |
3.3 Sexual reproduction processes
| Term | Definition |
|---|---|
| Pollination | Transfer of pollen from anther to stigma |
| Fertilisation in plants | Pollen reaches the ovule and male and female gametes fuse to form a zygote |
| Seed and fruit formation | Zygote develops into a seed; ovule becomes seed and ovary develops into fruit |
| Seed dispersal | Fruits or seeds are carried away by animals, wind or water |
| Germination | Seed uses stored food to grow roots and shoots when in suitable place |
| Fertilisation in animals | External fertilisation occurs in water for many fish and amphibians; internal fertilisation occurs inside the female's body for birds and most mammals |
| After fertilisation - birds | Birds lay eggs; embryo develops using food stored in the egg until hatching |
| After fertilisation - mammals | Most mammals give birth to live young; embryo develops inside the mother who supplies food and oxygen |
| Main difference (egg-laying vs mammals) | Egg-laying animals provide food inside the egg; mammals provide food to the embryo inside the mother's body |
4. Threats to Life and Responses
4.1 Main global challenges
- Climate change
- Biodiversity loss
- Pollution
4.2 Climate change - causes and effects
- Burning fossil fuels releases greenhouse gases such as carbon dioxide (CO2) and methane
- Excess greenhouse gases trap more heat and cause global warming
- Plants, trees and plankton normally absorb CO2 but excess CO2 adds more heat than Earth can absorb quickly
- Small temperature rise can melt ice caps and raise sea levels causing coastal flooding
- Small temperature rise can increase extreme weather events such as heavy rainfall, storms, droughts and heat waves
- Small temperature rise can cause extinction of plants and animals that cannot adapt quickly
- Long-term changes in temperature, rainfall and weather patterns are called climate change
4.3 Biodiversity loss
- Destroying habitats causes plants and animals to vanish
- Loss of species upsets food chains and ecosystems
- Losing species weakens nature's capacity to support life
4.4 Pollution
| Term | Definition |
|---|---|
| Air pollution - sources | Comes from factories, vehicles and burning fuels |
| Air pollution - effects | Harms human health, damages crops and causes smog and acid rain |
| Water and soil pollution - sources | Caused by industrial effluents, agricultural chemicals and plastic waste |
| Water and soil pollution - effects | Harms aquatic life, makes water unsafe and reduces crop yields |
| Soil pollution - food chain | Polluted soil can introduce toxins into the food chain |
4.5 International agreements and status
| Term | Definition |
|---|---|
| Montreal Protocol (1987) | Reduced chemicals (CFCs) that damaged the ozone layer |
| Earth Summit (1992) | Global meeting that promoted cooperation on environment and development |
| Kyoto Protocol (entered into force 2005) | Set binding emission reduction targets for some countries |
| Paris Agreement (2015) | Countries committed to limit global warming with goal to keep warming well below 1.5°C above pre-industrial levels |
| 2025 status | As of 2025 the world has not yet achieved the 1.5°C goal |
4.6 How individuals and communities can help
- Cut down on pollution by avoiding burning waste and reducing vehicle emissions
- Switch to cleaner energy such as solar and wind
- Use energy and water carefully by turning off lights, repairing leaks and using public transport or cycling
- Reduce, reuse and recycle materials such as paper, plastic, glass and metal
- Practice sustainable farming and waste management using organic methods and reducing chemical use
- Protect biodiversity by conserving habitats and planting native trees
- Community action where local communities manage natural resources wisely
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