Fossils and radiation tests show that the formation where the sample was found is 250 million years old, they said. Still, there is the possibility the bacteria somehow seeped into the salt more recently in small drops of water, said Chris McKay, a biologist at NASA's Ames Research Center. The testing of the organism was done inside a containment lab at the Pennsylvania campus. The scientists said they took pains to prevent contamination. The researchers believe the bacteria survived as a spore and metabolized very little or not at all over the years.
Spores are well-known for their longevity.
R. John Parkes of England's University of Bristol said in a Nature commentary. In 1995, researchers at California Polytechnic State University reported reviving Bacillus bacteria spores from the gut of a bee stuck in amber. The bee was estimated to be 25 million to 30 million years old. Since 1960, researchers have reported finding organisms up to 650 million years old in salt, but the findings were met with skepticism because of contamination fears. In any case, the latest study shows that life can exist inside a salt crystal.