13. Our Home: Earth, a Unique Life Sustaining Planet

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

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

Geodiversity is the variety of non-living natural features such as rocks, landforms and soils. The other options are about living things or weather.

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

A smaller Earth with the same density would have less mass. Its gravity would be weaker and could not hold the gases of the atmosphere.

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

Source of seeds: very light seeds and spores were carried by the wind. Some seeds may have been dropped by birds or carried by rainwater.

Conditions that helped:

• moisture from the monsoon rain,
• a little soil and dust collected in the cracks,
• sunlight and air, and
• a suitable warm temperature.

Effect on climate:

• The area becomes hotter, as there are no trees to give shade and cool the air.
• Less carbon dioxide is absorbed, which adds to global warming.
• Rainfall in the area may reduce or become irregular.

Effect on biodiversity:

• Plants and animals lose their habitat. Many may die or move away.
• Some animals may enter human areas, causing conflict.

Effect on water:

• Concrete does not let rainwater soak into the ground, so groundwater is not recharged.
• Without tree roots, soil gets washed into rivers and lakes, making the water muddy.
• Runoff from roads and buildings carries waste and pollutes water.

It is true that the Earth’s climate has changed in the past. But those changes happened very slowly, over thousands of years, due to natural causes.

Today’s warming is happening very fast, within about 150 years. It is mainly caused by human activities such as burning coal, petrol and diesel, and cutting forests. These add large amounts of carbon dioxide to the air, which traps heat.

Living things do not get enough time to adjust to such fast change. That is why present global warming is a serious problem, and we must act to reduce it.

• The magnetic field shields the Earth from high-energy particles coming from the Sun and space. Without it, these particles would hit the Earth and harm living beings.
• Over time, these particles could strip away parts of the atmosphere.
• Birds, turtles and fish that use the magnetic field to find their way during migration would get lost.
• Magnetic compasses would not work, and satellites and power systems could be damaged.

Three things needed:

1. Air with enough oxygen to breathe, at a suitable pressure.
2. Liquid water for drinking and growing food.
3. A suitable temperature, with protection from harmful radiation.

Hardest to replicate: a thick, protective atmosphere. It would have to supply oxygen, keep the temperature right and block harmful rays — all at once. Mars has very weak gravity and no strong magnetic field to hold such an atmosphere for long.

Cause: this is due to climate change. Burning fuels and cutting trees add greenhouse gases like carbon dioxide to the air. These trap heat, raise the temperature and disturb rainfall patterns.

Two ways to adapt:

1. Save water — rainwater harvesting, farm ponds and drip irrigation.
2. Grow suitable crops — crops that need less water and can bear heat, like millets. Planting more trees will also help.

Yes, all three would be badly affected.

• Life: there would be no oxygen to breathe and no carbon dioxide for plants. Harmful ultraviolet rays would reach the surface, as there would be no ozone layer.
• Temperature: days would be extremely hot and nights extremely cold, because no air would trap heat.
• Water: liquid water could not stay on the surface. It would evaporate and escape into space. There would be no clouds and no rain.

So life as we know it would not be possible.

Growing new plants from a part of the plant such as the stem, root or leaf is called vegetative propagation.

1. Potato — the ‘eyes’ (buds) on a potato grow into new plants.
2. Ginger — a piece of the underground stem grows into a new plant.
3. Money plant — a stem cutting kept in water or soil grows roots.
4. Sugarcane — stem pieces with nodes are planted to grow new plants.
5. Bryophyllum — new plants grow from buds on the edges of its leaves.