A man walks through a tunnel formed from crystals of permafrost outside the village of Tomtor.Maxim Shemetov/REUTERS A roundworm thawed from 46,000-year-old permafrost recently started having babies. Scientists have previously revived ancient bacteria and prehistoric viruses that had been trapped. Experts say these zombie viruses could one day pose a problem for humanity. Scientists recently revived a microscopic roundworm from 46,000-year-old Siberian permafrost that was so well preserved, it started having babies.