<P> The Antarctic ice sheet is one of the two polar ice caps of the Earth . It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth . It covers an area of almost 14 million square kilometres (5.4 million square miles) and contains 26.5 million cubic kilometres (6,400,000 cubic miles) of ice . Approximately 61 percent of all fresh water on the Earth is held in the Antarctic ice sheet, an amount equivalent to about 58 m of sea - level rise . In East Antarctica, the ice sheet rests on a major land mass, while in West Antarctica the bed can extend to more than 2,500 m below sea level . </P> <P> In contrast to the melting of the Arctic sea ice, sea ice around Antarctica was expanding as of 2013 . The reasons for this are not fully understood, but suggestions include the climatic effects on ocean and atmospheric circulation of the ozone hole, and / or cooler ocean surface temperatures as the warming deep waters melt the ice shelves . </P> <P> The icing of Antarctica began in the middle Eocene about 45.5 million years ago and escalated during the Eocene--Oligocene extinction event about 34 million years ago . CO levels were then about 760 ppm and had been decreasing from earlier levels in the thousands of ppm . Carbon dioxide decrease, with a tipping point of 600 ppm, was the primary agent forcing Antarctic glaciation . The glaciation was favored by an interval when the Earth's orbit favored cool summers but oxygen isotope ratio cycle marker changes were too large to be explained by Antarctic ice - sheet growth alone indicating an ice age of some size . The opening of the Drake Passage may have played a role as well though models of the changes suggest declining CO levels to have been more important . </P> <P> According to a 2009 study, the continent - wide average surface temperature trend of Antarctica is positive and significant at> 0.05 ° C / decade since 1957 . West Antarctica has warmed by more than 0.1 ° C / decade in the last 50 years, and this warming is strongest in winter and spring . Although this is partly offset by fall cooling in East Antarctica, this effect is restricted to the 1980s and 1990s . </P>

When did antarctica's permanent ice cap form
find me the text answering this question