Which component of Earth atmosphere acts as a protective shield by absorbing most of the Sun harmful ultraviolet (UV) radiation before it reaches the surface?

Introduction / Context:
Life on Earth is protected from a large part of the Sun harmful ultraviolet radiation by a natural shield in the atmosphere. Without this shield, rates of skin cancer, eye damage, and harm to plants and animals would be much higher. This question asks you to identify what exactly acts as that protective shield.

Given Data / Assumptions:

• Ultraviolet radiation from the Sun can damage living tissues and DNA.
• There is a region in the atmosphere that absorbs much of this ultraviolet radiation.
• Some man made chemicals affect this region negatively.
• The options include chemicals, the ozone layer, the ozone hole, and the greenhouse effect.

Concept / Approach:
The protective shield is the ozone layer, a region of relatively high ozone concentration located in the stratosphere. Ozone molecules absorb a large fraction of high energy ultraviolet B and ultraviolet C radiation, converting it into heat and preventing it from reaching the surface in full strength. Chlorofluorocarbons, on the other hand, destroy ozone and weaken this shield. The ozone hole is a thinning of this protective layer, not the shield itself. The greenhouse effect deals mainly with infrared heat trapping, not ultraviolet absorption. Therefore, the correct answer is the ozone layer present in the stratosphere.

Step-by-Step Solution:

Verification / Alternative check:
Environmental science sources explain that international agreements such as the Montreal Protocol were created to phase out chlorofluorocarbons in order to protect the ozone layer. They show graphs of ozone concentration in the stratosphere and the associated reduction in ultraviolet radiation at the surface. These materials clearly identify the ozone layer as the ultraviolet shield, confirming our choice.

Why Other Options Are Wrong:

• Chlorofluorocarbons are wrong because they damage the ozone layer instead of shielding Earth.
• The ozone hole is wrong because it is a region of reduced ozone and therefore weaker protection.
• The greenhouse effect is wrong because it concerns heat trapping and climate change, not ultraviolet absorption.

Common Pitfalls:
Students sometimes confuse ozone layer, ozone hole, and greenhouse effect because all three are related to atmosphere and environmental issues. A helpful way to separate them is to remember that ozone layer equals ultraviolet shield, ozone hole equals damage to that shield, and greenhouse effect equals heat trapping and global warming.

Final Answer:
Ozone layer present in the stratosphere