What is the primary function of the stratosphere in Earth's atmosphere?

The primary function of the stratosphere is its role in the absorption of ultraviolet (UV) radiation. This layer of the atmosphere, which lies above the troposphere and below the mesosphere, is characterized by the presence of ozone. Ozone molecules absorb a significant portion of the Sun’s harmful UV radiation, preventing it from reaching the Earth's surface. This protective function is vital for maintaining life on Earth, as excessive UV radiation can lead to various health issues, including skin cancer and cataracts, as well as detrimental effects on ecosystems and wildlife.

The other options represent different characteristics or functions of other layers or aspects of the atmosphere. The troposphere is primarily where most weather phenomena occur, making it the layer directly involved in meteorological conditions. Air mass formation primarily occurs in the lower layers of the atmosphere, particularly in the troposphere. The description of temperature decreasing with altitude is characteristic of the troposphere as well, while the stratosphere actually displays a temperature inversion where temperatures increase with altitude due to the ozone layer. Thus, the role of the stratosphere in absorbing UV radiation is what distinguishes it as the correct choice in this context.