Like Han Solo frozen in carbonite, bacteria entombed in Earth's polar ice sheets can live in a sort of suspended animation. The difference is the bacteria can persist this way for hundreds of thousands of years.

And now, with the ice melting at unprecedented rates, they are poised to re-enter the ecological scene, eliciting new worries about the effects of global warming.

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Extreme not only in age but also in number, the biomass of bacteria and other microbes beneath the ice sheets may be "more than 1,000 times that of all the humans on Earth," freelance writer Cheryl Katz reported this week in The Daily Climate and Scientific American.

"It's a way of recycling genomes," Montana State University microbiologist John Priscu told Katz. "You put something on the surface of the ice and a million years later it comes back out."

It's that "coming back out" part we should hope the scientists keep an eye on. They have already managed to revive creatures that last lived long before humans walked the planet: Louisiana State University microbiologist Brent Christner revived bugs encased in 750,000-year-old ice.

Older still may be the microbes that other research teams may soon encounter as they drill into subglacial lakes Vostok and Ellsworth, two bodies of water that sit beneath a mile or more of Antarctic ice and have been sealed off from the outer world for millions of years.

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Fortunately, the microbiologists say there is almost zero chance that any of their revival efforts could trigger a pandemic like the one that swept the globe in last year's Hollywood disaster film "Contagion."

Most of the bugs revived to date are similar to cold-loving bacteria that live in soil and in the oceans today. Their ideal living conditions are far too harsh for viruses and other human pathogens, which have evolved to live in warm, cozy places.

Still, the experts do have some bona fide concerns about what could happen as the ice releases its grip on these ancient bugs:

  • Thawing cells turn into a giant pile of compost that emits carbon dioxide and methane into the atmosphere, enhancing global warming. That kind of warming boost is already happening as Arctic permafrost thaws.

  • Ancient microbes, which are evolving within the ice, outcompete existing microbial populations, with unknown consequences. 

  • Ancient microbes, revived and flushed to the sea along with thawing ice, upset ocean chemistry and compete with modern seafaring microbes. 

  • Genes of ancient microbes mix with modern ones, swamping the seas with types of organisms no one has ever seen.

  • Ancient cells flushed to the ocean serve as nutrients that trigger blooms of modern bacteria that in turn use up all the oxygen in the water, destroying fish habitats and exacerbating ocean dead zones that are already occurring from other causes. 

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Photo: Han Solo in carbonite (Courtesy Lucasfilm)