The correct answer is option 'D' - Ozone layer. Let's delve into the details to understand why.

The Stratosphere:
The stratosphere is a layer of the Earth's atmosphere that lies above the troposphere and below the mesosphere. It is situated roughly between 10 and 50 kilometers (6-30 miles) above the Earth's surface. The stratosphere plays a crucial role in protecting life on Earth by containing the ozone layer, which absorbs harmful ultraviolet (UV) radiation from the sun.

The Ozone Layer:
The ozone layer is a region within the stratosphere that contains a higher concentration of ozone (O3) molecules. Ozone is a molecule made up of three oxygen atoms bonded together. This layer is located between approximately 10 and 50 kilometers (6-30 miles) above the Earth's surface.

Importance of the Ozone Layer:
The ozone layer is vital because it acts as a shield, absorbing most of the sun's harmful UV radiation. UV radiation can cause various health issues, including skin cancer, cataracts, and weakened immune systems. It can also harm ecosystems, including marine life, crops, and phytoplankton.

Formation and Stability of the Ozone Layer:
The ozone layer is formed and maintained by a balance of chemical reactions involving oxygen molecules (O2) and ozone (O3). Solar UV radiation breaks apart some oxygen molecules into individual oxygen atoms. These free oxygen atoms then react with other oxygen molecules to form ozone. The ozone molecules, in turn, absorb UV radiation and prevent it from reaching the Earth's surface.

Depletion of the Ozone Layer:
Human activities have led to the release of certain chemicals, called ozone-depleting substances (ODS), into the atmosphere. The most well-known ODS are chlorofluorocarbons (CFCs) and halons, which were commonly used in refrigerants, aerosol propellants, and fire extinguishing systems. ODS can reach the stratosphere and disrupt the balance of ozone formation and destruction, leading to ozone depletion.

Consequences of Ozone Depletion:
Ozone depletion allows more UV radiation to reach the Earth's surface, which can have adverse effects. Increased UV radiation can cause skin cancer, damage to the eyes, suppression of the immune system, and harm to marine ecosystems, agriculture, and the overall environment. To mitigate ozone depletion, the international community developed the Montreal Protocol in 1987, which regulates the production and consumption of ozone-depleting substances.

In conclusion, the stratosphere is a region of the atmosphere that contains the ozone layer. The ozone layer is crucial for protecting life on Earth by absorbing harmful UV radiation from the sun. Ozone depletion caused by human activities can have severe consequences, highlighting the importance of preserving and safeguarding the ozone layer.