Although the giant ice sheets that cover Antarctica formed by 14 million years ago, constant movement and replacement of this ice means that none of it today is older than about 1 million years. Air bubbles trapped in this ice when it formed provide a record of our atmosphere in the past. In this episode, I describe how ice cores can retrieve important paleoclimatic data on earth's history over the past 800,000 years. This record reveals cycles of climate change and the role of greenhouse gases in determining ice ages and interglacial periods over millennia. The origin and importance of ozone in our atmosphere also is discussed and how the ozone 'hole' formed over Antarctica.