<P> Each year, scientists from 28 different nations conduct experiments not reproducible in any other place in the world . In the summer more than 4,000 scientists operate research stations; this number decreases to just over 1,000 in the winter . McMurdo Station, which is the largest research station in Antarctica, is capable of housing more than 1,000 scientists, visitors, and tourists . </P> <P> Researchers include biologists, geologists, oceanographers, physicists, astronomers, glaciologists, and meteorologists . Geologists tend to study plate tectonics, meteorites from outer space, and resources from the breakup of the supercontinent Gondwana . Glaciologists in Antarctica are concerned with the study of the history and dynamics of floating ice, seasonal snow, glaciers, and ice sheets . Biologists, in addition to examining the wildlife, are interested in how harsh temperatures and the presence of people affect adaptation and survival strategies in a wide variety of organisms . Medical physicians have made discoveries concerning the spreading of viruses and the body's response to extreme seasonal temperatures . Astrophysicists at Amundsen--Scott South Pole Station study the celestial dome and cosmic microwave background radiation . Many astronomical observations are better made from the interior of Antarctica than from most surface locations because of the high elevation, which results in a thin atmosphere; low temperature, which minimises the amount of water vapour in the atmosphere; and absence of light pollution, thus allowing for a view of space clearer than anywhere else on Earth . Antarctic ice serves as both the shield and the detection medium for the largest neutrino telescope in the world, built 2 km (1.2 mi) below Amundsen--Scott station . </P> <P> Since the 1970s an important focus of study has been the ozone layer in the atmosphere above Antarctica . In 1985, three British scientists working on data they had gathered at Halley Station on the Brunt Ice Shelf discovered the existence of a hole in this layer . It was eventually determined that the destruction of the ozone was caused by chlorofluorocarbons (CFCs) emitted by human products . With the ban of CFCs in the Montreal Protocol of 1989, climate projections indicate that the ozone layer will return to 1980 levels between 2050 and 2070 . </P> <P> In September 2006 NASA satellite data revealed that the Antarctic ozone hole was larger than at any other time on record, at 2,750,000 km (1,060,000 sq mi). The impacts of the depleted ozone layer on climate changes occurring in Antarctica are not well understood . </P>

Who makes up most of the population of antarctica