Final answer:
The tropopause is the boundary between the troposphere and the stratosphere, characterized as the coldest part of the atmosphere and the point where the temperature begins to increase with altitude due to ozone absorption of UV radiation.
Step-by-step explanation:
The tropopause is the boundary between the troposphere and stratosphere. The troposphere is the lowest layer of Earth's atmosphere, extending from the surface to an altitude of about 11-13 km (7-8 miles). Within this layer, the temperature decreases with increasing altitude, reaching its coldest point at the tropopause. Beyond the tropopause is the stratosphere, where the temperature reversal occurs due to the absorption of ultraviolet (UV) radiation by the ozone layer. The presence of ozone is crucial to life on Earth as it absorbs harmful UV radiation from the Sun.