The ozone layer that absorbs much of the Sun harmful ultraviolet radiation is mainly found in the lower portion of which layer of Earth atmosphere?

Introduction / Context:
This question comes from atmospheric science and environmental studies. It asks where in the atmosphere the ozone layer is mainly located. The ozone layer plays a crucial role in protecting life on Earth by absorbing a large portion of the Sun harmful ultraviolet radiation, making this a frequently tested topic in exams.

Given Data / Assumptions:

• The focus is on the ozone layer and the atmospheric layer in which it is mainly found.
• The options list stratosphere, troposphere, mesosphere, and thermosphere.
• Basic knowledge of atmospheric layers is assumed.

Concept / Approach:
Earth atmosphere is divided into several layers based on temperature variation with height. The troposphere is the lowest layer where weather occurs. Above it lies the stratosphere, followed by the mesosphere and thermosphere at higher altitudes. The ozone layer is concentrated in the lower to middle stratosphere, roughly between 15 and 35 kilometres above Earth surface. Ozone in this region absorbs a significant fraction of ultraviolet B and ultraviolet C radiation from the Sun, protecting living organisms. Although small amounts of ozone also exist in the troposphere, they are not organised into a protective layer and can act as pollutants at ground level.

Step-by-Step Solution:

Verification / Alternative check:
Diagrams of the atmosphere in geography and environmental science books show a band labelled ozone layer within the stratosphere. They highlight how ozone concentration peaks at stratospheric heights and explain that this region is crucial in absorbing ultraviolet radiation. These same sources distinguish between beneficial ozone high in the stratosphere and harmful ozone produced near the ground by pollution, reinforcing that the protective layer is stratospheric, not tropospheric.

Why Other Options Are Wrong:

Troposphere, the lowest layer where weather occurs, is incorrect because, while small amounts of ozone can appear near the surface, the main protective ozone layer is not located there.

Mesosphere, the middle cold layer, is wrong because this layer lies above the stratosphere and is not the region with the highest ozone concentration.

Thermosphere, the very high temperature layer, is incorrect because it is much higher above the surface and contains ionised gases, not the dense ozone layer referred to in environmental discussions.

Common Pitfalls:
Some learners confuse the troposphere and stratosphere because they both are relatively close to the surface. Others may focus on the word ozone in news stories about ground level pollution and mistakenly associate the main ozone layer with the lowest atmospheric layer. To avoid this, remember the phrase stratospheric ozone when thinking of the protective ozone layer, and link tropospheric ozone with pollution and smog. Keeping this distinction clear helps you answer questions about atmospheric layers correctly.

Final Answer:
The ozone layer is mainly found in the lower portion of the Stratosphere, above the troposphere.