Ozone Hole

This year's hole in the Earth's protective ozone layer, which grew to be larger than Antarctica, is finally set to close this week. Acting like a shield, ozone absorbs UV light from the sun. Its absence means more of this high-energy radiation reaches the Earth, where it can harm living cells. The ozone layer is depleted by chemical reactions that involve the by-products of human-made chemicals that linger in the atmosphere. The size of the annual hole, which forms during the southern hemisphere's summer, is strongly dependent on weather conditions and boosted by cold. Despite these natural fluctuations, experts expect the hole to close permanently by 2050, in response to restrictions on ozone-depleting chemicals introduced in 1987. The current hole, which has been unusually large, is on track to last only a few days less than its counterpart last year, which was the longest-lived on record since 1979.