Bacteria are hardy little creatures, but even they have their limits. One of those was previously thought to be polar ice and snow, but a new study from the University of York has now directly observed bacteria living in those conditions in both the Arctic and Antarctic regions. That discovery has implications for our understanding of the planet's past climate, as well as where we might hope to find life elsewhere in the universe.

In areas like Greenland and the poles, permafrost is thought to do a great job of preserving a detailed time capsule of the climate from Earth's deep history, by locking gases from the atmosphere into snow as it compresses into ice. Ice cores have been used to measure things like air pollution and carbon levels in the atmosphere at different points in time. They usually stretch back hundreds of thousands of years, but have been sampled as far back as 2.7 million years.

These calculations are usually based on the fact that bacteria can't survive in those conditions, so their biological processes won't mess up the readings. But that assumption might not hold true, as scientists have now seen bacteria alive and well in that hostile environment.

Working at carefully quarantined sites in both the Arctic and Antarctic, the York researchers sterilized samples of snow with UV light, and compared them to untreated samples. In doing so, they found that the natural snow contained traces of methyl iodide, a by-product of certain bacteria. Their presence could affect the CO2 levels detected in ice cores, altering our understanding of the Earth's past climate.

"As microbial activity and its influence on its local environment has never been taken into account when looking at ice-core gas samples it could provide a moderate source of error in climate history interpretations," says Kelly Redeker, lead author of the new study. "Respiration by bacteria may have slightly increased levels of CO2 in pockets of air trapped within polar ice caps meaning that before human activity CO2 levels may have been even lower than previously thought."

The implications of that aren't good news. If the pre-Industrial era CO2 levels were lower than earlier estimates, that means human activity is having an even bigger impact on the climate now than we thought.

On the other hand, there is some potential good news to the find as well. The fact that bacteria can survive in this harsh environment bodes well for life on other planets, which we might have previously dismissed as too cold. Liquid water might not be a necessity for a planet to be deemed habitable after all – water ice could suffice.

"The fact that we have observed metabolically active bacteria in the most pristine ice and snow is a sign of life proliferating in environments where you wouldn't expect it to exist," says Redeker. "This suggests we may be able to broaden our horizons when it comes to thinking about which planets are capable of sustaining life."

In future, the researchers plan to look deeper into the ice caps to see if they can find signs of active bacteria further down.

The research was published in the Journal of the Royal Society Interface.

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