In winter, a band of sea ice surrounding the continent extends ice coverage from 13 million square kilometers to some 20 million square kilometers. For millions of years snow and ice have built up on the land, so that now all but 2% of the continent is buried under a permanent ice sheet. The ice sheet holds 90% of the worlds ice, which is 70% of its fresh water. Bound into the ice is a unique environmental record stretching back to more than one million years. The ice and air trapped when surface snow turned to ice, provide a continuous record of earth's climate and other variables, such as changes in atmospheric gas composition and volcanic fallout.
The ice sheet averages 2.4 kilometers thick (4.7 kilometers at it's thickest point). If all the ice were to melt, the level of the world's oceans would rise by 70 meters. If the weight of the ice were removed, it is estimated that the underlying rock would rise by 1000 meters. The Antarctic ice sheet is moving gradually outwards at speeds varying from a few meters to several kilometers each year. When it reaches the coast as glacial ice, it breaks off to form ice bergs.
Antarctica has not always been an icy continent. Two hundred million years ago, Antarctica was joined to Australia, Africa, India, New Zealand and South America in the giant, mid - latitude, continental landmass of Gondwana. When Gondwana broke apart some 60 million years ago, Antarctica became cold and geographically isolated forcing many species to extinction. The surviving life forms evolved to endure the harsh environments. Many of them, including emperor and Adelie penguins, are found nowhere else.
Mawson station in the foreground with the enormous ice plateau rising up behind to meet Mt Henderson