In the Earths atmosphere, harmful ultraviolet radiation in the stratosphere is mainly absorbed by which gas, thereby protecting living organisms?

Introduction / Context:
The stratosphere contains a layer of gas that plays a crucial role in protecting life on Earth by absorbing most of the Suns harmful ultraviolet radiation. Understanding which gas is responsible for this protective effect is important in environmental science and general knowledge. This question focuses on identifying the gas that forms the ozone layer and shields living organisms from excessive ultraviolet radiation.

Given Data / Assumptions:

• The stratosphere lies above the troposphere in the atmosphere.
• A specific gas forms a concentration region known as the ozone layer.
• Ultraviolet radiation can damage DNA and cause health problems such as skin cancer.
• We assume a basic knowledge of atmospheric composition.

Concept / Approach:
Ozone is a molecule composed of three oxygen atoms and is represented as O3. In the stratosphere, ozone molecules absorb high energy ultraviolet B and ultraviolet C radiation from the Sun. This absorption prevents most of the harmful radiation from reaching the Earths surface. Normal diatomic oxygen, O2, does absorb some ultraviolet radiation but not as effectively in the dangerous wavelengths. Sulphur dioxide and argon are present in much smaller amounts and do not form a protective layer against ultraviolet radiation. Therefore, the gas responsible for this function is ozone.

Step-by-Step Solution:
Step 1: Recall that the ozone layer is located in the stratosphere. Step 2: Understand that this layer is rich in ozone molecules, O3. Step 3: Recognise that ozone strongly absorbs high energy ultraviolet radiation, especially ultraviolet B and ultraviolet C. Step 4: Compare with other gases like oxygen, sulphur dioxide and argon, which do not provide the same level of ultraviolet protection as a distinct layer. Step 5: Conclude that ozone is the gas responsible for absorbing ultraviolet radiation in the stratosphere.

Verification / Alternative check:
Environmental science resources describe the ozone layer in the stratosphere as a vital shield that protects living organisms on land and in shallow water from damaging ultraviolet radiation. Data showing ozone depletion and the appearance of an ozone hole over polar regions are linked with increases in ultraviolet radiation at the surface and related health risks. These discussions consistently identify ozone, O3, as the key absorbing gas in this context.

Why Other Options Are Wrong:
Option a, sulphur dioxide, is a pollutant gas mainly produced by burning fossil fuels and volcanoes and is associated with acid rain rather than ultraviolet absorption.

Option c, oxygen, does absorb some ultraviolet radiation at higher altitudes, but the specific and concentrated protective layer is formed by ozone, not by ordinary oxygen alone.

Option d, argon, is an inert noble gas present in small amounts in the atmosphere and does not play a significant role in ultraviolet absorption.

Common Pitfalls:
Students sometimes confuse oxygen and ozone because both are forms of the same element. Another mistake is to think that any atmospheric gas can absorb ultraviolet radiation equally, which is not true. Remembering that the term ozone layer always refers to the protective ultraviolet absorbing region composed mainly of ozone helps avoid these errors.

Final Answer:
Ultraviolet radiation in the stratosphere is mainly absorbed by Ozone.