Question 1

Identify and explain the five main spheres of the Earth system and give one example of each.

Accepted Answer

The five main spheres of the Earth system are:
1. Geosphere: solid rocks, soil, landforms (e.g., Deccan plateau).
2. Hydrosphere: all liquid water like oceans and rivers (e.g., Ganga–Brahmaputra river system).
3. Cryosphere: solid water such as glaciers and polar ice caps (e.g., Himalayan glaciers).
4. Atmosphere: the layer of gases surrounding Earth (e.g., air in forests).
5. Biosphere: all living organisms and their habitats (e.g., mangroves).
These spheres interact continuously to support life and Earth's processes. — Earth's system is composed of five interacting spheres. The Geosphere includes land and rocks; the Hydrosphere includes all forms of liquid water; the Cryosphere is solid water like ice; the Atmosphere is the air layer; and the Biosphere includes all life forms. Each sphere influences and is influenced by others, forming a complex system.

Question 2

Fig. 13.1 shows features of the Earth's surface including mountains, lakes, snow, air, and vegetation. Identify which feature represents the cryosphere and explain how snow from the cryosphere can become part of a lake in the hydrosphere.

Accepted Answer

The snow-covered mountains represent the cryosphere. Snow melts due to temperature rise and the meltwater flows downhill, eventually feeding into lakes, which are part of the hydrosphere. — In Fig. 13.1, the snow on mountain peaks is the cryosphere (solid water). When temperatures rise, snow melts and the water runs off into lakes and rivers, thus transferring water from the cryosphere to the hydrosphere. This process links the spheres through the water cycle.

Question 3

How does warming of Arabian Sea water affect the southwest monsoon in India?

Accepted Answer

Warming of Arabian Sea water increases evaporation, leading to more moisture in the atmosphere. This causes fluctuations in the southwest monsoon, resulting in variable rainfall patterns, including floods in some regions and droughts in others. — Higher sea surface temperatures increase evaporation rates, adding moisture to the air. This affects monsoon winds and rainfall distribution, causing irregular monsoon behavior that impacts agriculture and water availability.

Question 4

What is the solar constant, and what is its approximate value? Why is it important for understanding Earth's climate?

Accepted Answer

The solar constant is the average amount of solar energy received per unit time per unit area perpendicular to the Sun's rays at the top of Earth's atmosphere. Its value is about 1.4 kilowatts per square metre (1.4 kW/m²). It is important because it represents the energy input that drives Earth's climate and weather systems. — The solar constant quantifies the energy Earth receives from the Sun before atmospheric absorption. Knowing this helps scientists understand Earth's energy balance and predict climate and weather patterns.

Question 5

Calculate the amount of solar energy received by a 1 m² area in one hour if the insolation on Earth's surface is 1 kW/m².

Accepted Answer

3.6 × 10⁶ J — Given:
Intensity = 1 kW/m² = 1000 J/s/m²
Area = 1 m²
Time = 1 hour = 3600 s

Find:
Energy received (E)

Formula:
E = Intensity × Area × Time

Solution:
Step 1: E = 1000 J/s/m² × 1 m² × 3600 s
Step 2: E = 3,600,000 J

Answer:
E = 3.6 × 10⁶ J

Note: Students often forget to convert time to seconds or confuse units.

Question 6

Fig. 13.2 shows the electromagnetic spectrum. Which types of electromagnetic radiation from the Sun reach the Earth's surface in significant amounts, and what are their roles?

Accepted Answer

Ultraviolet, visible, and infrared; they heat Earth and support photosynthesis — Solar radiation reaching Earth is mainly ultraviolet (UV), visible, and infrared (IR). UV is mostly absorbed by ozone protecting life; visible light drives photosynthesis; infrared warms Earth's surface. Gamma rays and X-rays are absorbed by upper atmosphere; microwaves and radio waves carry little energy for warming.

Question 7

Explain the term 'albedo' and describe how it affects the temperature of Earth's surfaces with examples.

Accepted Answer

Albedo is the fraction of solar radiation reflected by a surface. Surfaces with high albedo reflect more sunlight and stay cooler, such as snow (albedo 0.80–0.90). Surfaces with low albedo absorb more sunlight and become warmer, like black soil and ocean water. — Albedo influences how much solar energy is absorbed or reflected. High albedo surfaces like snow keep polar regions cold by reflecting sunlight, while low albedo surfaces absorb heat, warming the area.

Question 8

Complete the missing albedo values in Table 13.1 for light coloured soil, black soil, and ocean water based on typical ranges.

Accepted Answer

0.20–0.30 / 0.05–0.10 / 0.06–0.10 — Light coloured soil typically has albedo around 0.20–0.30, black soil about 0.05–0.10, and ocean water about 0.06–0.10. These values indicate that lighter soils reflect more sunlight than darker soils and water.

Question 9

Why do cities experience higher temperatures than surrounding rural areas, especially during summer and at night? Explain the urban heat island effect.

Accepted Answer

Cities have more built-up areas made of concrete, steel, and asphalt that absorb and retain solar radiation, re-radiating heat and raising temperatures compared to rural areas. This phenomenon is called the urban heat island effect. — Materials in cities have low albedo and high heat capacity, causing them to heat up and retain warmth longer. Vegetation in rural areas provides shade and cooling through transpiration, making them cooler.

Question 10

Fig. 13.5 illustrates solar radiation and warming of the Earth. Which surfaces in the figure would have the highest and lowest albedo? Explain your answer.

Accepted Answer

Snow-covered surfaces have the highest albedo as they reflect most solar radiation, while dark surfaces like black soil or ocean water have the lowest albedo because they absorb more sunlight. — In the figure, white or light-colored areas such as snow reflect 80–90% of sunlight (high albedo), keeping them cool. Dark surfaces absorb more radiation, heating up the surface. This difference causes temperature variations.

Question 11

Explain how the latitude of a place affects the amount of solar radiation it receives and its temperature.

Accepted Answer

Latitude affects solar radiation because the Sun's rays strike near the equator at a steep angle, concentrating energy over a smaller area, resulting in higher temperatures. Towards the poles, rays strike at a slant, spreading energy over a larger area, causing cooler temperatures. — Due to Earth's spherical shape, sunlight intensity varies with latitude. This uneven heating causes temperature gradients that influence climate and weather patterns globally.

Question 12

Describe the role of the ozone layer in protecting life on Earth and its position in the atmosphere.

Accepted Answer

The ozone layer is located in the stratosphere (12–50 km above Earth) and absorbs most of the Sun's harmful ultraviolet (UV) radiation, protecting living organisms from damage. — By filtering UV rays, the ozone layer prevents skin cancer and eye damage in humans and protects ecosystems. It also contributes to atmospheric heating in the stratosphere.

Question 13

Fig. 13.7 depicts the layers of Earth's atmosphere. Name these layers in order from the surface upwards and mention one key feature of each.

Accepted Answer

The layers from Earth's surface upward are:
1. Troposphere: weather occurs here, temperature decreases with height.
2. Stratosphere: contains ozone layer, temperature increases with height.
3. Mesosphere: temperature decreases with height.
4. Thermosphere: very high temperatures, ionized gases.
5. Exosphere: outermost layer, merges into space. — Each atmospheric layer has distinct temperature gradients and functions. The troposphere supports life and weather; stratosphere protects with ozone; mesosphere burns meteors; thermosphere contains ionosphere; exosphere fades into space.

Question 14

What is the greenhouse effect, and how do greenhouse gases maintain Earth's temperature suitable for life?

Accepted Answer

The greenhouse effect is the trapping of outgoing infrared radiation by greenhouse gases like carbon dioxide, methane, and water vapor, which keeps the Earth warm enough to support life. — Solar radiation warms Earth's surface, which emits heat as infrared radiation. Greenhouse gases absorb and re-radiate some heat back, preventing excessive cooling. Without this effect, Earth would be too cold for life.

Question 15

Assertion (A): The Earth's surface heats unevenly because of its spherical shape and tilt of its axis.
Reason (R): The Sun's rays strike the equator at a steep angle and the poles at a slant.
A) Both A and R are true and R is the correct explanation of A
B) Both A and R are true but R is NOT the correct explanation of A
C) A is true but R is false
D) A is false but R is true

Accepted Answer

A) Both A and R are true and R is the correct explanation of A
Explanation: The Earth's spherical shape causes sunlight to spread over larger areas near poles and concentrate near the equator. The tilt of Earth's axis causes seasonal variations. Thus, uneven heating results from these factors. — Assertion is true because Earth's shape and tilt cause uneven solar radiation distribution. Reason correctly explains that the angle of sunlight varies with latitude, causing this uneven heating.

Earth as a System

Earth as a System — Study Notes

Earth as a System: Energy, Matter, and Life

13.1 Uneven Heating of the Earth

13.1.1 Interaction of solar radiation on the Earth's surface

Practice Questions — Earth as a System

All 13 Chapters in Exploration