Billions of viruses are raining down on you from the upper atmosphere every day

The next time you go outside and look up, think about this: as you stare up into the sky, billions of tiny invisible viruses are raining down on you.

Earlier this year researchers at the University of British Columbia, with colleagues in the U.S. and Spain, revealed work that showed that billions of viruses, and smaller numbers of bacteria, are routinely swept up high into the atmosphere by dust storms and ocean spray.

They're able to travel vast distances at altitudes exceeding 3,000 metres, crossing continents and oceans, and then rain down upon the earth in a microbial deluge, largely unseen and unnoticed by humans.

"We found the same viruses pretty much everywhere in the planet," Curtis Suttle, co-author of the study and a microbiean ecologist at UBC, told Quirks & Quarks host Bob McDonald.

"We would find the same viruses in a meltwater pond in the Arctic Ocean, or in the Gulf of Mexico, or in a lake in Germany. [It] was puzzling to use because we wouldn't expect the same host organisms to exist in all those different environments."

Suttle's research partners sampled viruses circulating in the high atmosphere from mountaintop stations high in the Sierra Nevada mountains of Spain. There, they were able to reach into the planetary boundary layer, where the air circulates more freely than it can closer to the ground.

They found that more than 800 million viruses per square metre are deposited into the atmosphere every day.

"That's an area that we think is relatively pristine. So if there's billions being deposited every day above the planetary boundary later, then certainly when we're closer to the surface of the Earth, there's far more," said Suttle.

He reassured McDonald that the vast majority of these viruses pose no threat to the health of humans or other animals: most of them infect bacteria, which also travel in the air in numbers about one-tenth that of the viruses.

In fact, we interact with billions of viruses on a daily basis with no negative effects on our health.

"The average concentration of viruses in seawater, for example, is on the order of a billion to five billion viruses in every millilitre of water," he said.

"So for every time you go swimming, just for the water you take into your mouth, you swallow more viruses than there are people in North America."

Suttle estimates that viruses kill about 20 per cent of life (again, mostly bacteria) in the ocean every day. That may seem ghastly, but it actually means they're responsible for a massive recirculation and recycling of nutrients that's vital for biological productivity.

"The natural cycle of the planet is in order to have life, we have to have death as well. And so the viruses are responsible for a large proportion of that turnover," he said.

"They're our friends, not our enemies."