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

1. What is one major reason Mars cannot currently support life like Earth?
(i) It has too many volcanoes.
(ii) It is too close to the Sun.
(iii) It lacks a thick atmosphere and liquid water.
(iv) Its magnetic field is too strong.
See AnswerThe correct answer is (iii) It lacks a thick atmosphere and liquid water. As we learned, Mars’s atmosphere is about 100 times thinner than Earth’s, which is not enough to support life as we know it or to effectively trap heat. While scientists believe Mars may have had liquid water in the past, it does not have it on its surface today, and liquid water is essential for life to evolve and thrive.

2. Which of these is an example of geodiversity?
(i) Variety of bird chirping in a forest.
(ii) Different landforms like mountains, valleys, and deserts.
(iii) Changing weather during monsoons.
(iv) Number of different types of fish in a pond.
See AnswerThe correct answer is (ii) Different landforms like mountains, valleys, and deserts. Geodiversity refers to the variety of non-living parts of nature, such as rocks, soil, and landforms. The other options are examples of biodiversity (variety of life) or weather patterns.

3. If the Earth were smaller with the same density, what might happen to its atmosphere?
(i) It would become thicker and hotter.
(ii) It would escape into space due to weaker gravity.
(iii) It would become frozen.
(iv) It would cause stronger winds.
See AnswerThe correct answer is (ii) It would escape into space due to weaker gravity. A smaller planet would have a weaker gravitational pull. This weak gravity would not be strong enough to hold onto the gas molecules of the atmosphere, and they would gradually drift off and escape into space, just like what happened on Mercury and to a large extent on Mars.

4. In sexual reproduction, why are offspring different from their parents?
(i) They grow in different climates.
(ii) They eat different food.
(iii) They acquire new instructions after birth.
(iv) They get mixed instructions (genes) from both parents.
See AnswerThe correct answer is (iv) They get mixed instructions (genes) from both parents. During sexual reproduction, a new individual is formed from the combination of special reproductive cells, called gametes, from two different parents. Each gamete contains half of the parent’s genetic instructions. This mixing of genes from two sources creates a unique combination in the offspring, making them different from both parents and also from their siblings.

5. You notice tiny green plants growing in cracks on your school wall after the monsoon. Where do you think the seeds came from? What conditions helped these plants grow there?
See AnswerIt’s a wonderful observation! The seeds most likely arrived in one of two ways: they could have been carried by the wind and got stuck in the crack, or they were dropped there by a bird that had eaten a fruit. As the book mentions, a bird might eat a fruit and excrete the seed, which could land in a crack in a wall. The monsoon provided the perfect conditions for them to grow. The cracks in the wall would have collected some dust and soil, which acted as a base. The monsoon rains provided the necessary water, and of course, they had access to sunlight and air. It shows just how resilient life can be!

6. A city has recently cut down a large patch of forest to build new roads and buildings. Discuss the possible effects this could have on the local climate and biodiversity? How might this affect water availability or quality in the area?
See AnswerCutting down a forest, an act known as deforestation, has several serious effects.
For local climate and biodiversity: The forest acts like a natural air conditioner; removing it can lead to higher local temperatures. Trees also play a huge role in the water cycle through transpiration, so their removal can lead to less rainfall in the area. For biodiversity, this is a disaster. The forest was a home, or habitat, for countless animals, birds, insects, and other plants. Destroying it means these living things lose their food and shelter, forcing them to move away or die out, which drastically reduces local biodiversity.
For water availability and quality: Forest soil is excellent at absorbing rainwater, which slowly seeps into the ground to recharge groundwater. Without the trees and their roots holding the soil, rainwater will run off the bare ground quickly, causing soil erosion and increasing the risk of floods. This runoff can carry pollutants from the city into nearby rivers and lakes, damaging water quality. With less water seeping into the ground, the underground water table could also drop, reducing water availability in the long run.

7. A friend says, “The Earth has always had climate changes in the past, so today’s global warming is nothing new.” How would you respond using what you’ve learnt in this and other chapters of your science book?
See AnswerThat’s a very interesting point my friend makes. I would say this: “You’re right that the Earth’s climate has changed naturally over millions of years. However, the climate change we are experiencing today is very different and alarming for two main reasons: its speed and its cause. The current warming is happening much, much faster than any natural warming cycles in the past. More importantly, this rapid change is caused by human activities. By burning massive amounts of fossil fuels like coal and oil, we are releasing extra carbon dioxide that was stored underground for millions of years. Our planet’s natural systems, like forests and oceans, can’t absorb this extra carbon fast enough. This is trapping more heat in the atmosphere, causing the rapid global warming we see today.”

8. Imagine Earth’s magnetic field suddenly disappeared. What kinds of problems could arise for life on Earth? Explain.
See AnswerIf Earth’s magnetic field disappeared, we would be in serious trouble! The magnetic field acts like an invisible shield protecting us from harmful radiation. Without it, two major problems would arise. First, a constant stream of high-energy particles from the Sun, called the solar wind, would hit our atmosphere directly. This would slowly strip the atmosphere away, thinning it out over time. Second, the shield protects us from dangerous cosmic rays from deep space. Without the magnetic field, these particles and other harmful UV rays from the sun would reach the surface. This increased radiation could damage the cells of living organisms, leading to widespread health issues and making it very difficult for life, as we know it, to survive.

9. You are tasked with designing a new settlement for humans on Mars. Name three things you would need to recreate from Earth to support human life there. Which of these do you think is the hardest to replicate, and why?
See AnswerTo build a settlement on Mars, I would need to recreate three essential things from Earth:
1. A breathable atmosphere: We would need a contained habitat filled with a mix of gases like oxygen and nitrogen that we can breathe safely.
2. Liquid water: We would need to find a source of water on Mars (likely frozen underground) and create systems to melt, purify, and recycle it for drinking, growing food, and sanitation.
3. A stable food source: We would need to set up a system for growing plants, perhaps through hydroponics, inside the habitat to provide food and also help recycle the air.
I think the hardest of these to replicate and sustain on a large scale is the breathable atmosphere. While we can create it in a small, sealed habitat, creating and maintaining a thick, protective atmosphere for an entire planet is an unimaginably huge task. It would involve changing the entire planet’s chemistry and climate, which is far beyond our current technology. Water and food systems are complex, but they are challenges on a much smaller, more manageable scale.

10. In a village, the temperature has been increasing and rainfall has become unpredictable over the past few years. What could be causing this change? Suggest two ways the village could adapt to these new conditions.
See AnswerThe increasing temperature and unpredictable rainfall are classic signs of local climate change, which is driven by the larger issue of global warming. The burning of fossil fuels worldwide is the primary cause. Locally, deforestation in the surrounding areas could also be making the problem worse by affecting rainfall patterns and increasing temperatures.
To adapt, the village could take two important steps:
1. Water Management: To deal with unpredictable rainfall, they could implement rainwater harvesting. This involves collecting rainwater from rooftops and other surfaces in large tanks or directing it to underground wells to recharge the groundwater. This stored water can be used during dry spells.
2. Afforestation: The villagers could start a tree-planting drive in and around the village. Trees provide shade, which helps cool the area. They also improve the soil’s ability to hold water and can help stabilize local rainfall patterns over time.

11. If there were no atmosphere on the Earth, would it affect life, temperature and water on the planet? Explain.
See AnswerAn Earth without an atmosphere would be a completely different and lifeless world.
Effect on Life: Life as we know it would be impossible. The atmosphere contains oxygen, which most living things need for respiration. It also contains the ozone layer, which protects us from the Sun’s harmful ultraviolet (UV) radiation. Without it, life couldn’t exist.
Effect on Temperature: The planet would experience extreme temperatures. During the day, it would get scorching hot, and at night, it would become freezing cold. The atmosphere acts like a blanket, trapping some of the Sun’s heat through the greenhouse effect to keep the planet warm and stable. Without it, all the heat would radiate back into space at night, leading to a drastic drop in temperature.
Effect on Water: All the liquid water would be gone. The extreme cold at night would freeze it, and the lack of atmospheric pressure would cause the water to boil away into space during the day. An atmosphere is crucial for maintaining the right pressure and temperature for water to exist as a liquid.

12. Discuss five examples of vegetative propagation.
See AnswerVegetative propagation is a fascinating way for plants to reproduce without seeds, using parts like their stem, root, or leaf. Here are five common examples:
1. Potato: We can grow a whole new potato plant from a piece of a potato that has an ‘eye’. The eye is actually a bud that sprouts into a new stem and leaves.
2. Ginger: Ginger grows from a special underground stem called a rhizome. If you plant a piece of the rhizome in soil, it will sprout roots and shoots to become a new plant.
3. Money Plant: This is very easy to do at home. If you cut a piece of the stem and place it in water or moist soil, it will develop roots and grow into a completely new plant.
4. Sugarcane: Farmers plant short sections of the sugarcane stalk, called setts, in the soil. Buds on these sections sprout to grow into new sugarcane plants.
5. Rose: You can grow a new rose bush by taking a cutting from the stem of an existing plant and planting it in the soil. It will develop its own roots and grow.