What role does the ozone layer play for living organisms?

The ozone layer plays a critical role in protecting living organisms by absorbing the majority of the sun's harmful ultraviolet (UV) radiation. Without the presence of the ozone layer, increased levels of UV radiation would reach Earth's surface, leading to harmful effects such as increased skin cancer rates in humans and damage to the immune system. Additionally, excessive UV exposure can harm terrestrial and aquatic ecosystems, affecting organisms ranging from phytoplankton in the oceans to various plants and animals on land. This protective mechanism is vital for maintaining the health of ecosystems and the life they support.

In contrast, the other options refer to different functions or concepts that do not accurately describe the role of the ozone layer. The maintenance of Earth's temperature is primarily related to greenhouse gases, while the ozone layer is not a direct source of oxygen or involved in carbon dioxide absorption.