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Our Home: Earth, a Unique Life Sustaining Planet - What Are the Threats to Life on Earth?

Grade 8CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Global Warming: The gradual increase in the Earth's average temperature due to the accumulation of greenhouse gases like Carbon Dioxide (CO2CO_2), Methane (CH4CH_4), and Nitrous Oxide (N2ON_2O).

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Greenhouse Effect: A natural process where certain gases trap heat in the atmosphere, keeping Earth warm. However, human activities have intensified this, leading to climate change.

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Ozone Layer Depletion: The thinning of the Ozone (O3O_3) layer in the stratosphere caused by Chlorofluorocarbons (CFCsCFCs), which allows harmful Ultraviolet (UVUV) radiation to reach Earth.

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Acid Rain: Rainwater mixed with pollutants like Sulfur Dioxide (SO2SO_2) and Nitrogen Oxides (NOxNO_x), forming acids such as H2SO4H_2SO_4 and HNO3HNO_3, which damage soil, water bodies, and monuments.

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Deforestation: The large-scale removal of trees, which disrupts the CO2−O2CO_2 - O_2 balance, reduces biodiversity, and causes soil erosion.

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Pollution: Contamination of air, water, and land by harmful substances (pollutants) resulting from industrialization, urbanization, and agricultural runoff.

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Loss of Biodiversity: The extinction or reduction of plant and animal species due to habitat destruction, hunting, and climate change.

📐Formulae

6CO2+6H2O→Sunlight/ChlorophyllC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{Sunlight/Chlorophyll} C_6H_{12}O_6 + 6O_2

3O2→UV Radiation2O33O_2 \xrightarrow{UV \, Radiation} 2O_3

SO2+H2O→H2SO3 (Sulphurous acid)SO_2 + H_2O \rightarrow H_2SO_3 \text{ (Sulphurous acid)}

2NO2+H2O→HNO2+HNO3 (Nitrous and Nitric acid)2NO_2 + H_2O \rightarrow HNO_2 + HNO_3 \text{ (Nitrous and Nitric acid)}

💡Examples

Problem 1:

A forest area was measured at 8,000,0008,000,000 hectares. Over a decade, 3,456,7893,456,789 hectares were lost due to deforestation and urban expansion. Calculate the remaining forest area.

Solution:

8000000−34567894543211\begin{array}{r} 8000000 \\ - 3456789 \\ \hline 4543211 \end{array}

Explanation:

To find the remaining forest cover, we subtract the lost area from the initial total area. The remaining forest area is 4,543,2114,543,211 hectares.

Problem 2:

Explain the chemical reaction that occurs when Sulfur Dioxide (SO2SO_2) released from factories reacts with rainwater to form acid rain.

Solution:

SO2(g)+H2O(l)→H2SO3(aq)SO_2(g) + H_2O(l) \rightarrow H_2SO_3(aq) followed by oxidation to form H2SO4(aq)H_2SO_4(aq)

Explanation:

Sulfur dioxide reacts with water vapor in the atmosphere to form Sulfurous acid. This acid falls as acid rain, lowering the pHpH of soil and water bodies, which is harmful to aquatic life and plants.

Problem 3:

If the concentration of CO2CO_2 in a sample of air is 0.04%0.04\%, express this concentration in parts per million (ppm).

Solution:

Concentration in ppm=0.04×10,000=400 ppmppm = 0.04 \times 10,000 = 400 \text{ ppm}

Explanation:

Percentage means parts per hundred. To convert to parts per million, we multiply the percentage by 10,00010,000 since 1,000,000/100=10,0001,000,000 / 100 = 10,000.

What Are the Threats to Life on Earth? Class 8 Notes & Examples