Imagine sticking some bacteria in the freezer and taking them out millions of years later to find that they are still alive.
That would be similar to what happened recently, when scientists brought eight-million-year-old microbes back to life—simply by thawing them.
The ancient bacteria were found frozen in the world's oldest known tracts of ice, the debris-covered glaciers of Antarctica.
"We think that they were pretty much locked in a frozen, inanimate state for that period of time," said lead study author Kay Bidle, a marine microbiologist at Rutgers University in New Brunswick, New Jersey.
It's also possible that some of the microbes were capable of maintaining their metabolism within tiny droplets of water suspended in the ice, Bidle said.
Bidle and colleagues retrieved and revived two samples of bacteria from the glacial ice. The first was a hundred thousand years old, and the second was around eight million years old.
The eight-million-year-old bacteria were alive, but barely.
Their genes were severely damaged from long exposure to cosmic radiation, which is higher at Earth's poles.
The radiation bombarded the bacteria's DNA with high-energy particles, which broke apart the DNA's chemical bonds and hacked it into shorter pieces.
Big Bacterial Thaw
Most of the bacteria in the samples probably blew over from African deserts, said study co-author Paul Falkowski, a biochemist at Rutgers.
Once the bacteria landed on the glacier's snowy surface, they were compressed with the snow to form ice.
"These ices are literally gene banks," he added.
That's because bacteria are able to incorporate foreign DNA into their own genetic makeup in a process called horizontal gene transfer.
This gives bacteria a way to pick up new advantageous traits, which in turn speeds up their evolution.
Falkowski likens the Antarctic ice to a "genetic popsicle."
As glaciers and ice caps melt as a result of the current trend of global warming, vast amounts of bacterial genetic material might be flushed into the ocean.
"You basically have this mechanism by which you're freeing up encased DNA and microbes that may be viable," lead author Bidle said.
Scraps of bacterial DNA might get incorporated into today's marine microbes, or viable bacteria released from the ice might also grow and impact the ecosystem.
"How that's going to play out, we don't know," Bidle said. He and Falkowski plan to focus future work on how current ice melting impacts modern microbes' genetic diversity.
The study appears in this week's journal Proceedings of the National Academy of Sciences.
Meaning for Mars?
The finding also lends hope to the possibility that microbes could lie in a similar suspended state in ancient Martian ice.
But it also nixes the idea that life could hitch a ride on comets between solar systems.
"Each solar system is an island of life," Falkowski said. Microbes on comets would be exposed to lethal doses of cosmic radiation for millions of years during their journey, he said.
"Under those conditions you would be sterilizing comets."
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