The state of stratospheric ozone depletion

Ozone, composed of three molecules of oxygen bonded together, forms a protective barrier in the Earth's upper atmosphere. The greatest concentration of ozone molecules, about 90 percent of all found on the planet, is found about 15 miles (25 km) above the Earth's surface in the stratosphere. This concentration is what scientists refer to as the ozone layer. Ozone shields the Earth from harmful ultraviolet (UV) radiation that damages all living things on the planet.