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Scientists say there could be something frozen ground that contains many deadly diseases. Ancient microbes have been trapped millennia in the permafrost that covers large areas Earth. Permafrost is ground that stays completely frozen for least two years. It is common high in mountains and the North and South Poles. The scientists say the permafrost is melting because climate change. The result could be the release unknown, harmful viruses, which scientists are calling 'Factor X'. Birgitta Evengard, a professor infectious diseases at a university in Sweden, said we know little Factor X and the biological dangers trapped Earth's permafrost.

Virologist Jean-Michel Claverie says there are viruses deep the permafrost that are more than 50,000 years old. He said these could be harmful to humans. Professor Claverie said "ancient viruses to a million years old" would be the most terrifying because they are unknown and we have never encountered them before. He added that deadly bacterial diseases smallpox and anthrax could be released a large scale. Factor X could pose even bigger problems. However, many scientists agree that a bigger danger melting permafrost is the release methane. This is a greenhouse gas that is 80 times more harmful than CO2.

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