Solutions-NCERT-Class-8-Science-Curiosity-Chapter-13-Our Home: Earth, a Unique Life Sustaining Planet-CBSE

If there were no life on Earth at all, the planet would look very different and much less dynamic.

• No green colour: There would be no forests, grasslands, or crops. Earth would look mostly brown, grey, and blue—bare rocks, deserts, mountains, and oceans with no plants or algae.
• Silent and empty land: There would be no animals, birds, or insects. No sounds like chirping, buzzing, or movement—just wind, waves, and volcanic or geological activity.
• Different atmosphere: Without plants and microorganisms, oxygen levels would be extremely low. Carbon dioxide would build up, and the air would not be breathable for humans.
• Lifeless oceans: Oceans would exist, but without fish, plankton, or coral reefs. The water might look clear or chemically different, but it would be biologically empty.
• No soil as we know it: Soil forms with the help of living organisms. Without life, Earth’s surface would mostly be rock and dust, making the land harsh and unstable.
• More extreme climate: Life helps regulate Earth’s climate. Without it, temperatures could become more extreme, with hotter days and colder nights.

In short, Earth would still be a planet with land, water, and air—but it would be a quiet, barren, and lifeless world, more like a rocky planet than the living Earth we know today.

Life on Earth has continued for billions of years because it is resilient, adaptable, and well supported by Earth’s natural systems. Several key reasons explain this survival:

• Ability to adapt and evolve: Living organisms change over generations through evolution. When conditions change some organisms have traits that help them survive and reproduce. Over time, life adapts to new environments.
• Genetic variation: Especially through sexual reproduction, organisms show differences among themselves. This variation increases the chance that some individuals can survive diseases, climate changes, or other challenges.
• Diversity of life: Earth has millions of species living in different habitats—land, water, air, hot springs, ice, and deep oceans. Even if a disaster wipes out many species, some life forms usually survive elsewhere.
• Simple life forms are very tough: Microorganisms like bacteria can survive extreme heat, cold, radiation, and lack of oxygen. After major disasters, these simple life forms often survive and help restart ecosystems.
• Earth’s stable life-support systems: Earth’s atmosphere, oceans, magnetic field, and cycles of water and nutrients help protect life and allow it to recover after disturbances.
• Ecosystem recovery: Natural processes like nutrient recycling by decomposers help ecosystems rebuild after destruction, such as after volcanic eruptions or forest fires.

Because of these reasons, life on Earth does not easily disappear. Even after mass extinctions and disasters, life finds a way to continue and evolve.

• Dogs and hens reproduce differently because they belong to different groups of animals with different reproductive methods.
• Dogs are mammals, and mammals give birth to live young. The baby develops inside the mother’s body, where it gets nourishment and protection, and is born fully formed.
• Hens are birds, and birds lay eggs. In birds, the embryo develops inside a hard-shelled egg outside the mother’s body, which protects the growing chick.
• These methods developed through evolution and are best suited to each group’s body structure and way of life.

• Not easily. Plants would not be able to grow normally on Mars, even if soil and water were taken there.
• Mars has a very thin atmosphere with almost no oxygen and very little carbon dioxide pressure, so plants cannot survive well.
• The planet is also extremely cold, and most water would freeze or evaporate quickly.
• Mars lacks a strong magnetic field and ozone layer, so harmful radiation would damage plant cells. In addition, Martian soil contains toxic chemicals that are unsafe for plant growth.
• Plants might grow only inside special sealed habitats (like greenhouses) where temperature, air, water, and radiation are carefully controlled.

• Earth is unique because it has the right conditions to support life.
• It is at the correct distance from the Sun, which keeps the temperature suitable for liquid water.
• Earth has abundant water, essential for all life processes.
• A protective atmosphere provides oxygen for breathing, carbon dioxide for plants, and keeps the planet warm.
• The ozone layer and magnetic field protect life from harmful radiation.
• Earth’s stable climate, suitable gravity, and rich soil allow plants, animals, and microorganisms to grow and survive together.

No, temperature or distance from the Sun is not the only factor that makes Earth habitable.

• Earth also has liquid water, which is essential for life.
• Its atmosphere provides oxygen, carbon dioxide, and a suitable pressure for living organisms, while the greenhouse effect keeps the planet warm.
• A strong magnetic field and ozone layer protect Earth from harmful radiation.
• In addition, Earth has suitable gravity, a stable climate, and the right mix of soil and nutrients.

All these factors together make Earth a planet where life can survive and thrive.

• If the Earth were too small, its gravity would be weak. It would not be able to hold its atmosphere, so air would escape into space, making life impossible—similar to what happened on Mars. Living organisms would also struggle to survive without stable air and water.
• If the Earth were too big, its gravity would be very strong. This strong gravity could crush complex life forms, make movement difficult, and greatly affect breathing and circulation. The atmosphere might also become too thick, creating extreme pressure and temperatures.
• So, Earth’s right size and gravity are important for maintaining air, water, and conditions suitable for life.

Yes, Earth’s magnetic field plays an important role in sustaining life.

• It acts like a protective shield that deflects harmful charged particles coming from the Sun (solar wind) and from deep space.
• Without this protection, these particles could strip away the atmosphere, damage the ozone layer, and expose living organisms to dangerous radiation.
• By protecting the atmosphere and surface, Earth’s magnetic field helps create safe conditions for life to survive and thrive.

Life on Earth is sustained by the constant interaction between four major systems, or "spheres," which together regulate climate, cycle nutrients, and support all ecosystems.

• Atmosphere: The layer of air surrounding the Earth. It provides oxygen for respiration and carbon dioxide for photosynthesis. The greenhouse effect maintains suitable temperature and weather helps in the distribution of water.
• Hydrosphere: Includes all forms of water on Earth such as oceans, rivers, lakes, groundwater, and ice. Water is essential for life processes, transport of nutrients, regulation of body temperature, and provides habitat for aquatic organisms.
• Geosphere: Consists of the solid parts of Earth like rocks, soil, minerals, and landforms. It provides soil and nutrients for plant growth, minerals for human use, and different landforms that create varied habitats.
• Biosphere: Comprises all living organisms—plants, animals, and microorganisms. It forms ecosystems where producers, consumers, and decomposers interact to maintain balance and recycle nutrients.

Earth’s gravity, soil, and nutrient cycles, along with interactions between the atmosphere, hydrosphere, geosphere, and biosphere, help maintain a stable environment where life can grow, survive, and reproduce.

Bamboo and sugarcane usually grow into new plants by vegetative propagation, not by seeds.

In these plants, new shoots grow from the stem.

• Sugarcane is grown by planting pieces of its stem, called setts, which have buds. These buds grow into new plants.
• Bamboo spreads through underground stems (rhizomes) that produce new shoots nearby.

(iii) It lacks a thick atmosphere and liquid water.

(ii) Different landforms like mountains, valleys, and deserts.

(ii) It would escape into space due to weaker gravity.

(iv) They get mixed instructions (genes) from both parents.

• The seeds most likely came from the surroundings. They were carried to the wall cracks by wind, rainwater, birds, or insects. Some seeds may also have been present in dust or soil trapped in the cracks. For example, a bird eating a fruit may have dropped or excreted the seed into the crack.
• After the monsoon, favourable conditions helped the plants grow. Rain provided enough moisture, the cracks collected soil and nutrients, and sunlight was available for photosynthesis. Warm weather during the monsoon also supported seed germination and growth.

Cutting down a large forest can have serious effects on the local environment.

• Effects on local climate: Trees help cool the air through shade and transpiration. When forests are removed, temperatures can rise, making the area hotter and drier. Rainfall may become irregular because fewer trees release water vapour into the atmosphere, and strong winds and heat waves may increase.
• Effects on biodiversity: Deforestation destroys habitats, forcing animals to migrate or die, and many plant species may disappear. This reduces biodiversity and disrupts food chains and ecosystems.
• Effects on water availability and quality: Trees help rainwater seep into the ground and recharge groundwater. Without forests, rainwater runs off quickly, causing floods during heavy rains and water shortage during dry periods. Soil erosion increases, washing mud and pollutants into rivers and lakes, which lowers water quality.

Overall, cutting forests disturbs the natural balance and negatively affects climate, living organisms, and water resources in the area.

• It is true that Earth’s climate has changed naturally in the past, but today’s global warming is different.
• Earlier climate changes happened very slowly due to natural causes like volcanic activity or changes in Earth’s orbit.
• The current warming is happening much faster and is mainly caused by human activities, especially burning fossil fuels and cutting forests.
• Because the change is so rapid, many plants, animals, and even human systems do not have enough time to adapt.
• This is why today’s global warming is a serious concern, not just a natural cycle.
• Unlike past changes, current warming requires urgent action, like using renewable energy, to protect ecosystems.

If Earth’s magnetic field suddenly disappeared, life on Earth would face serious problems.

The magnetic field protects Earth by deflecting harmful charged particles from the Sun and outer space.

Without it,

• These particles would directly hit Earth and could strip away the atmosphere, including the ozone layer.
• This would allow dangerous ultraviolet and cosmic radiation to reach the surface, damaging living cells and increasing diseases like cancer.
• Many organisms, especially humans, animals, and plants, would struggle to survive. Satellites, communication systems, and power grids would also be damaged, affecting human life.

Therefore, the loss of Earth’s magnetic field would make the planet far less safe and less suitable for life.

To support human life on Mars, three important Earth-like conditions would need to be recreated:

1. A breathable atmosphere: Humans need oxygen to breathe and proper air pressure to survive. Mars has a very thin atmosphere, so sealed habitats with oxygen supply would be essential.
2. Liquid water: Water is needed for drinking, growing food, and daily activities. Systems would be required to extract, melt, purify, and recycle water on Mars.
3. Protection from radiation: Earth’s magnetic field and atmosphere protect us from harmful solar and cosmic radiation. On Mars, humans would need strong shielding, such as underground habitats or thick protective walls.

The hardest to replicate would be radiation protection because Mars lacks a natural magnetic field and thick atmosphere. Creating an Earth-like protective shield for the whole planet is extremely difficult, so protection would have to be limited to small living areas.

The change in temperature and unpredictable rainfall is likely due to climate change, mainly caused by human activities such as cutting trees, increased use of fossil fuels, and changes in land use around the village. Loss of vegetation can also disturb the local water cycle and increase heat.

Ways the village can adapt:

1. Water conservation: Build rainwater harvesting systems and use efficient irrigation methods like drip irrigation to manage irregular rainfall.
2. Planting trees and climate-resilient crops: Growing more trees can reduce heat, and using drought- or flood-resistant crop varieties can help farmers cope with changing weather.

Yes, without an atmosphere, Earth would be unable to support life.

• Life would be affected because there would be no oxygen for breathing and no carbon dioxide for plants to make food. Harmful radiation from the Sun would reach the surface directly, damaging living organisms.
• Temperature would become extreme. Without the atmosphere and greenhouse effect, Earth would be very hot during the day and extremely cold at night, making survival impossible.
• Water would also be affected. Liquid water would not exist—it would either freeze or quickly evaporate into space. Rivers, lakes, and oceans would disappear, making life impossible on Earth.

Vegetative propagation is asexual reproduction where plant parts like stems, roots, or leaves grow into new plants.

Five examples:

1. Money Plant: A stem cutting with a node grows roots when placed in water or soil, forming a new plant.
2. Potato: The "eyes" (buds) on a sprouted potato can be planted to grow a new potato plant.
3. Ginger: A piece of ginger rhizome with a bud, when planted in soil, develops into a new plant.
4. Sugarcane: Stem cuttings with nodes are planted to produce new sugarcané plants, as sugarcane rarely produces seeds.
5. Bamboo: Sections of bamboo stems or rhizomes can be planted to grow new bamboo plants, relying on vegetative propagation.