What is the primary function of the ozone layer?

The primary function of the ozone layer is to keep most ultraviolet (UV) light from reaching the Earth. The ozone layer is composed of ozone (O3) molecules, which absorb the majority of the sun's harmful UV radiation. This absorption is crucial for protecting living organisms, as excessive UV radiation can lead to a variety of health issues, including skin cancer, cataracts, and compromised immune systems. Additionally, UV radiation can have detrimental effects on ecosystems, particularly phytoplankton in the oceans, which are foundational to marine food webs.

Other functions described in the choices do not pertain to the role of the ozone layer. Regulating atmospheric pressure is a function related to the overall balance of gases in the atmosphere. While oxygen is essential for life, the ozone layer does not produce oxygen; instead, it primarily serves to block harmful radiation. Finally, controlling weather patterns involves complex atmospheric dynamics that are not directly influenced by the ozone layer; those patterns are driven by factors such as temperature, moisture, and atmospheric circulation. Thus, the characterization of the ozone layer as a barrier to UV light emphasizes its critical protective role in sustaining life on Earth.