riverat1 writes: In a news release from Purdue University a new study finds that CO2 level dropping below ~600 ppmv lead to the formation of the Antarctic ice sheet about 33.7 million years ago. The team studied geochemical remnants of ancient algae from cores drilled in geologically stable areas of the ocean floor. The focus was on two sites in the tropical Atlantic Ocean. Mark Pagani, the Yale geochemist who led the study cautioned it doesn't necessarily mean the ice sheet will melt at 600 ppmv of CO2 and said even if we reach the tipping point it will take thousands of years to completely melt it. The study is published in Science Magazine (paywalled).