The Fossils of animals also reveal this & plants found in the border areas.
Along the polar front, the cold Antarctic surface water's plunge below the warmer sub-Antarctic water, marking the boundaries of Antarctic Ocean. This natural boundary is also termed as Antarctic convergence.
The first traces of continental glaciers in Antarctica date back almost 50 million years. The fossils found indicate that the climate at this period was still generally temperate. A general cooling trend set in about 38 million years ago, but great accumulations of ice extended more & more frequently ever the continent during the last 20 million years ,after the drake passage had opened up & created one continuous Southern Ocean. Since then an uninterrupted circumpolar current has flowed from West to East through the Southern Ocean, isolating Antarctic waters and keeping them cold. The oceanic circulation around Antarctica initiated a positive feedback process by which the polar regions,especially Antarctica, act as the 'Cold Sinks' of the thermodynamic engine represented by the atmosphere and the Global Oceans.
The Antarctic Ice : .
About 98.5 percent of Antarctica covered by a thick ice sheet which is termed as the ice cap. It is estimated that 90 percent of the world's fresh water lies in Antarctica in the form of Ice. It is therefor the Antarctic's most important potential natural resource. Inspite of the presence of so much of fresh water reserve in Antarctica, the continent is termed as the driest continent due to extreme low temperatures, the capacity of air to hold the moisture is very low. The continent receives 120 to 150 mm of water in the form of snow every year. The rate of accumulation is highest near the coast due to high temperatures, and lowest in the interior in higher latitudes. The accumulated ice thickness is as high as 4,776m in East Antarctica,with an average of 2000m over the continent.