Paleo Slide Set: The Ice Ages
Northern hemisphere glacial and estimated sea ice coverage.
Medium-sized ice caps covering thousands of square kilometers in sub-polar 
and Polar Regions are also considered to be glaciers. The world's largest 
glaciers include the huge ice shelves that stretch out hundreds of kilometers 
over the oceans and seas of the Arctic and Antarctic. In recent geologic times 
there have also been enormous ice sheets as thick as four kilometers 
that blanketed most of Antarctica and Greenland.

Scientists have been working to understand the mysteries surrounding the world's 
glaciers for over a century and a half, By examining the physical and chemical 
properties and geologic record of glaciers, and creating advanced computer models 
to simulate glacial growth, flow and melting mechanisms, our understanding of ice 
on earth has vastly improved, inspiring new questions and necessitating more research 
into the power and dynamic qualities of glacier.

This image compares modern day glacier and ice coverage of the northern hemisphere 
with the same region 18,000 years before present. Note that the modern sea ice 
coverage is during the summer months; winter coverage is more extensive.

Photo Credits:
Mark McCaffrey
NGDC/NOAA