Chapter 8 – Composition and Structure of Atmosphere
- What is the atmosphere?
The atmosphere is a layer of gases surrounding Earth, held by gravity. It protects life, moderates temperature, and allows weather and climate patterns to exist. - What are the major gases in the atmosphere?
Nitrogen (78%), Oxygen (21%), and Argon (0.93%) are the major gases. Others like carbon dioxide, neon, and helium exist in trace amounts. - What is the role of nitrogen in the atmosphere?
Nitrogen is inert and essential for plant growth. It maintains atmospheric stability and supports the nitrogen cycle through fixation and decomposition processes. - Why is oxygen important in the atmosphere?
Oxygen supports life through respiration and combustion. It’s vital for all aerobic organisms and makes up about 21% of the atmosphere. - What is the significance of carbon dioxide?
Although just 0.04%, CO₂ is essential for photosynthesis and is a greenhouse gas responsible for trapping heat and contributing to global warming. - What are variable components of the atmosphere?
They include water vapor, ozone, dust particles, and carbon dioxide. Their quantity varies with place and time and significantly affects weather and climate. - What is water vapor and why is it important?
Water vapor contributes to humidity and cloud formation. It regulates Earth’s temperature and drives the hydrological cycle through evaporation and precipitation. - What is the function of ozone?
Ozone in the stratosphere absorbs harmful ultraviolet (UV) rays from the Sun, protecting life. However, ground-level ozone is a pollutant. - How does dust influence weather?
Dust particles act as nuclei for condensation, helping cloud formation. They also scatter and absorb sunlight, impacting visibility and temperature. - What are the five layers of the atmosphere?
The five layers are: Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere. Each has unique temperature gradients and characteristics. - What is the troposphere?
The lowest layer (up to 8–18 km), where weather occurs. Temperature decreases with height. It contains most of the atmospheric mass and water vapor. - What is the tropopause?
It is the boundary between the troposphere and stratosphere. It acts as a barrier, preventing mixing of layers and halting vertical cloud development. - What is the stratosphere?
Extending from about 18 km to 50 km, it contains the ozone layer and sees a temperature increase with altitude due to UV absorption. - Why is the stratosphere ideal for flying aircraft?
It has stable air and minimal weather disturbances, making it suitable for jet planes and long-distance flights. - What is the mesosphere?
Located between 50 km and 80 km, it has the coldest temperatures in the atmosphere and burns up meteors entering from space. - What is the thermosphere?
Ranging from 80 km to 400 km, temperature rises with altitude. It contains ionized gases and is the region where auroras and satellites exist. - What is the exosphere?
The outermost layer, merging with outer space beyond 400 km. It contains very thin air, mainly hydrogen and helium, with almost no atmospheric pressure. - What causes temperature variations in atmospheric layers?
Temperature changes due to solar radiation absorption, altitude, and atmospheric composition. For instance, UV rays heat the stratosphere, while the troposphere cools with height. - What are the characteristics of the ionosphere?
It lies in the thermosphere and contains ionized particles. It reflects radio waves, enabling long-distance communication. - What is the significance of the atmosphere?
It protects Earth from meteors and harmful radiation, supports life by providing oxygen and carbon dioxide, and regulates Earth’s temperature. - Why does the atmosphere become thinner with altitude?
Due to gravity, air pressure and density decrease with height. Over 99% of air mass lies below 32 km altitude. - How is atmospheric pressure related to altitude?
Atmospheric pressure decreases rapidly with altitude because the weight of the overlying air becomes less as we go higher. - What is lapse rate?
It is the rate at which temperature decreases with altitude in the troposphere—typically 6.5°C per 1000 meters. - What are greenhouse gases?
These gases trap heat in Earth’s atmosphere. Key examples include carbon dioxide, methane, nitrous oxide, and water vapor. - What is the greenhouse effect?
It is the process by which greenhouse gases absorb and re-radiate heat, warming the Earth’s surface and maintaining a habitable climate. - Why is ozone depletion harmful?
It increases UV radiation reaching Earth, leading to skin cancer, eye damage, and harm to plants and marine life. - What causes ozone depletion?
Chlorofluorocarbons (CFCs) and other pollutants break down ozone molecules in the stratosphere, thinning the ozone layer especially over polar regions. - How is the atmosphere essential for water cycle?
The atmosphere enables evaporation, condensation, cloud formation, and precipitation, forming a complete cycle of water movement on Earth. - How is the composition of air measured?
Air composition is measured using instruments like spectrometers, gas analyzers, and balloons that sample air at various altitudes. - Why is the study of atmosphere important in geography?
Understanding atmospheric structure and composition helps analyze weather, climate, global warming, pollution, and natural hazards like storms and droughts.