The ozone layer in the Earth's stratosphere blocks most ultraviolet (UV) radiation emitted by the sun in the UV-B range (with a wavelength of 280-315 nanometres) from reaching the Earth's, and therefore the ocean's, surface. Consequently, stratospheric ozone depletion since the 1970s has been a concern. International action to address that depletion has been taken under the Montreal Protocol on Substances that Deplete the Ozone Layer, and the situation appears to have stabilized, albeit with some variation from year to year. A potential effect of ultraviolet radiation on nanoparticles of titanium dioxide has, however, been identified.