SSC Selection Post 2025 PYQ — Question 21

Correct Answer

The lowest layer of the atmosphere

Explanation

The troposphere is the lowest and densest layer of Earth's atmosphere. It extends from the Earth's surface up to an average height of about 13 kilometers, varying from roughly 8 kilometers at the poles to 18 kilometers at the equator. This layer is crucial for life as it contains approximately 75% of the atmosphere's total mass and nearly all of its water vapor and aerosols. Because of this high concentration of moisture and thermal activity, almost all weather phenomena—such as clouds, rain, snow, and storms—occur exclusively within the troposphere. As you ascend through this layer, the temperature decreases at a standard rate known as the environmental lapse rate, which is about 6.5 degrees Celsius for every 1 kilometer of altitude.

Key Points

The boundary that separates the troposphere from the overlying stratosphere is called the tropopause, where the temperature stops decreasing with height and becomes stable.

The stratosphere sits directly above the troposphere and contains the ozone layer, which protects life on Earth by absorbing harmful ultraviolet radiation from the sun.

The highest and outermost layers include the mesosphere, thermosphere, and exosphere, which gradually transitions into outer space.

Important Questions and Answers

Question: Why do almost all weather events take place only in the troposphere layer?

Answer: This occurs because the troposphere contains nearly all of the atmosphere's water vapor, moisture, and dust particles, along with strong convective air currents that drive weather systems.

Question: What is the average rate at which temperature decreases with altitude in the troposphere?

Answer: The temperature drops at a normal lapse rate of approximately 6.5 degrees Celsius per kilometer (or about 3.5 degrees Fahrenheit per 1,000 feet) of ascent.