The correct answer is: B. Ozone layer.
The ozone layer is a region of Earth’s stratosphere that absorbs most of the Sun’s ultraviolet radiation. It contains high concentrations of ozone (O3) relative to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth’s atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 kilometers (12 to 19 mi) above Earth, although its thickness varies seasonally and geographically.
The ozone layer is important because it protects life on Earth from harmful ultraviolet radiation. Ultraviolet radiation can cause skin cancer and other health problems, and it can also damage plants and animals. The ozone layer absorbs most of the Sun’s ultraviolet radiation, preventing it from reaching the Earth’s surface.
The ozone layer is constantly being created and destroyed. Ozone is created when ultraviolet radiation splits oxygen molecules (O2) into two oxygen atoms (O). These oxygen atoms then combine with oxygen molecules to form ozone (O3). Ozone is destroyed when it reacts with other chemicals, such as chlorine and bromine.
Human activities have been shown to have a significant impact on the ozone layer. Chlorofluorocarbons (CFCs), which were once widely used in refrigerants and aerosol propellants, are one of the main causes of ozone depletion. CFCs are released into the atmosphere, where they rise into the stratosphere and break down under the influence of ultraviolet radiation. This releases chlorine atoms, which react with ozone molecules, destroying them.
The Montreal Protocol, an international treaty signed in 1987, has helped to reduce the use of CFCs and other ozone-depleting substances. As a result, the ozone layer is slowly recovering. However, it is important to continue to protect the ozone layer by reducing our use of ozone-depleting substances and by taking other measures to reduce our impact on the environment.
The other options are incorrect because:
- The ionosphere is a region of Earth’s atmosphere that is ionized by solar radiation. It is important for radio communications and for the formation of auroras.
- The troposphere is the lowest layer of Earth’s atmosphere. It is where most of Earth’s weather occurs.
- The magnetosphere is a region of space around Earth that is created by the Earth’s magnetic field. It protects Earth from harmful radiation from the Sun and other sources.