Molecular oxygen absorbs high-energy sunlight in the UV-C radiation, at wavelengths shorter than about 240 nm, to form ozone. While UV-B radiation can get through the atmosphere and reach the surface of the Earth, it can only do so in lesser amounts than UV-A radiation. UV-C radiation, on the other hand, is entirely absorbed by the atmosphere and does not reach the surface. The most harmful kind of UV radiation is UVC.