Question

How are the following caused and what is the effect of each of them on our environment?
(i) Depletion of ozone layer (ii) Acid rain
OR
What is meant by soil erosion? Describe two practices by which soil erosion can be prevented.

Answer 1

When CFCs reach the stratosphere, the ultraviolet radiation from the sun causes them to break apart and release chlorine atoms which react with ozone, starting chemical cycles of ozone destruction that deplete the ozone layer. One chlorine atom can break apart more than 100,000 ozone molecules.

Acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidicpollutants, known as acid rain.



Soil erosion is defined as the wearing away of topsoil. Topsoil is the top layer of soil and is the most fertile because it contains the most organic, nutrient-rich materials. One of the main causes of soil erosion is watererosion, which is the loss of topsoil due to water.

Answer 2

(i) Depletion of ozone layer

Reduced ozone levels as a result of ozone depletion mean less protection from the sun’s rays and more exposure to Ultra radiation at the Earth’s surface. Studies have shown that in the Antarctic, the amount of Ultra  measured at the surface can double during the annual ozone hole.

(ii) Acid rain

Acid rain, also called acid precipitation or acid deposition, precipitation possessing a pH of about 5.2 or below primarily produced from the emission of sulfur dioxide and nitrogen oxides from human activities, mostly the combustion of fossil fuels. In acid-sensitive landscapes, acid deposition can reduce the pH of surface waters and lower biodiversity.

ΔWhat is meant by soil erosion?

Removal of topsoil faster than the soil forming processes can replace it, due to natural, animal, and human activity -over grazing, over cultivation, forest clearing, mechanized farming, etc.

Soil erosion results in land infertility and leads to desertification and devastating flooding. It is estimated that 20 percent of the world's topsoil was lost during 1950-1990, and its loss is continuing at a faster rate.

Two ways which prevent Soil Erosion:

• Vegetation: The simplest and most natural way to prevent erosion is through planting vegetation. Plants establish root systems, which stabilizes soil and prevents soil erosion.

• Avoid soil compaction.