: The largest virus found to date was discovered buried about 30 meters down in the permafrost of northeast Siberia, where it has probably lain for tens of thousands of years. About 1.5 micrometers in length, the so-called Pithovirus
poses no threat to humans, according to researchers. It is, however, lethal to amoebas. The find points up the possibility that other such giant viruses, long thought extinct and potentially harmful to humans, could turn up as global warming melts permafrost. But giant viruses may also contain genes never before seen in living things and thus yield clues to the origin of life on Earth.