Ozone occurs naturally in both the troposphere and stratosphere. Stratospheric ozone is beneficial as it filters out UV radiation and protects life on Earth. However, certain man-made pollutants called ozone-depleting substances have led to a thinning of the ozone layer, especially over Antarctica where it forms an "ozone hole". This depletion increases UV radiation levels and poses risks to human health, agriculture, and marine life. In response, the 1989 Montreal Protocol was enacted to phase out ozone-depleting substances, though full recovery of the ozone layer is not expected until 2050.