The seasonal "ozone hole" over the South Pole has disappeared again after reaching record size earlier this year, U.N. officials said. The hole is a thinner-than-usual area in the protective layer of gas high up in the Earth's atmosphere. It has been forming in the extremely low temperatures that mark the end of Antarctic winter every year since the mid-1980s, largely due to chemical pollution. The hole forms in August or September as Antarctica's long, dark winter is ending. It normally fills in by December.