>> doug: it's fresh water ice and the ice itself varies from the snow, like today. and then down at the bottom, ice that might have fallen as snow 35,000 years ago. it's the part of the antarctic ice sheet we call the buttress, because it fringes the entire continent. it might take 50,000 years for the ice itself to get into the raw sea and bust off as an iceberg. but it would take only 20,000 years or even 10,000 years if the ice shelf wasn't there. this is the biggest pile of free ice in the solar system. >> anthony: mcmurdo is at the tip of ross island, surrounded by miles of frozen sea. there are a lot of different types of ice down here. >> doug: glaciology started about 50 years ago. our entire science is driven by the fact that we're still trying to figure out what antarctica is doing in terms of sea level. how the ice sheet is expanding