Microorganisms locked in Antarctic ice for 100,000 years and more came to life and resumed growing when given warmth and nutrients in a laboratory.
Researchers tested five samples of ice ranging in age from 100,000 years to 8 million years.
"We didn't really know what to expect. We knew that microorganisms were really hardy," Kay Bidle, an assistant professor of marine and coastal sciences at Rutgers University, said in a telephone interview. Bidle is the lead author for the research, appearing in Monday's online edition of Proceedings of the National Academy of Sciences.
The researchers tested samples of the oldest known ice on Earth and had success at growing bacteria from the younger samples.
Microorganisms from the older ice didn't do as well, growing only very slowly. Some of the oldest microorganisms were watched for as long as a year, Bidle said, compared to the week or so it usually takes to culture bacteria.
Calling the ice cores "gene popsicles," the researchers found evidence of some of the most common bacteria still around, including firmicutes, proteobacteria and actinobacteria.
These are microorganisms that have been around a long time, Bidle said, "not something Earth hasn't seen before."
The researchers found that the DNA in bacteria deteriorates sharply after about 1.1 million years.
Bidle said that after 1.1 million years the size of the DNA gets cut in half. In the oldest ice it consisted of just 210 units strung together. Normally the DNA of the average bacterium has about 3 million units.
Studying these life forms helps in "understanding the geological and physiological limits of life on Earth under different conditions," he explained.
In addition, there is interest in looking for life on other planets and how long microorganisms might have remained viable under cold, icy conditions on places like Mars.
Finally, he added, most of life on Earth consists of microbes. "They live in every possible environment ... so learning about microbes and what they can withstand and what their limits are is important to understanding how the Earth works over long periods of time."
The project was developed by Rutgers' Paul Falkowski, and other members of the research team include SangHoon Lee of South Korea’s Polar Research Institute and David Marchant of Boston University. The research was supported by the Gordon and Betty Moore Foundation, the U.S. National Science Foundation and the Korea Antarctic Research Program.
This revised report clarifies the roles of all the researchers involved in the project.