In 1999, Scott Rogers from Bowling Green State University in Ohio and his colleagues reported finding a common plant pathogen that had survived being entombed in ice for 140,000 years.
As global warming melts the world's ice sheets, rising sea levels are not the only danger. Viruses hidden for thousands of years may thaw and escape - and we will have no resistance to them.
Some scientists believe that climate change could unleash ancient illnesses as ice sheets drip away and bacteria and viruses defrost. Illnesses we thought we had eradicated, like polio, could reappear, while common viruses like human influenza could have a devastating effect if melting glaciers release a bygone strain to which we have no resistance. What is more, new species unknown to science may re-emerge. And it is not just humans who are at risk: animals, plants and marine creatures could also suffer as ancient microbes thaw out.