The Ozone Hole Ozone imaging of Earth from TOMS, March 9, 2001. Note the lower levels of Ozone over Antarctica. Since the 1920's, scientists have been measuring the amount of ultraviolet light reaching the surface of the Earth at sites around the globe and using this information to estimate the amount of ozone in the ozone layer above that site. They found that the level of ozone changes over time. In general, the ozone layer is thickest over the north and south poles and thinnest over the equator.
Most ozone is created over the tropics and then is carried to higher latitudes by prevailing winds.
Beginning in the mid-1970's, scientists at the British Antarctica Survey noticed lower than normal measurements in the ozone layer over the continent. The ground-based measurements were confirmed by satellite readings, and when results were announced in 1985, the ozone hole became a big story. The so-called hole is a thinning of the layer, rather than an actual hole. Ozone levels change naturally. They can fluctuate because of change of seasons, the wind, and sunspot activity.