More Than 800 Million Viruses Fall Through the Skies Every Day in a Single Square Meter

Updated | The sky is absolutely riddled with viruses swept up from the surface of the planet. For the first time, researchers have measured the number of viruses swarming around the atmosphere—and how many are falling back down to Earth.

The team found billions of viruses traveling through the skies, which they believe could explain the spread of remarkably similar viruses across wildly different areas of the globe.

Virus transportation

Probing the atmosphere from sites high in the Sierra Nevada mountains in southern Spain, the team discovered enormous numbers of viruses being swept up above 9,000 feet.

"Every day, more than 800 million viruses are deposited per square meter (11 square feet) above the planetary boundary layer," explained University of British Columbia virologist Curtis Suttle, a senior author of the research published in International Society for Microbial Ecology Journal, in a statement.

The planetary boundary layer, which sits in the lowest part of the troposphere, responds to conditions at the Earth's surface. For the first time, the scientists measured the number of viruses in the upper troposphere, which lies above the planet's weather systems but below the stratosphere. Viruses travel upwards on the back of sea spray and soil-dust. They can then soar thousands of miles through the upper troposphere before settling back on Earth.

The results shed light on the way these viruses spread across the planet. Suttle explains: "Roughly 20 years ago we began finding genetically similar viruses occurring in very different environments around the globe…It's quite conceivable to have a virus swept up into the atmosphere on one continent and deposited on another."

The team found far fewer bacteria above the planetary boundary layer, with only tens of millions deposited per square meter. The team think this is because viruses have a lot more atmospheric sticking power than bacteria, where bacteria are carried away by rain.

"Bacteria and viruses are typically deposited back to Earth via rain events and Saharan dust intrusions. However, the rain was less efficient removing viruses from the atmosphere," said author and microbial ecologist Isabel Reche from the University of Granada in Spain.

This might all sound terrifying, but the authors actually believe such a microbe transportation mechanism can help ecosystems thrive. They wrote: "Rather than being a negative consequence, this deposition provides a seed bank that should allow ecosystems to rapidly adapt to environmental changes."

Publich health implications

Many of the viruses falling to Earth are not likely to be active.

Reche told Newsweek: "The deposition rates of viruses are huge, but still we need to determine what type of viruses and their viability to infect their hosts."

A more pertinent concern is the increased loading of particles into the atmosphere itself—viruses or not. This activity is usually associated with respiratory problems, Reche said.

A changing climate will continue to drive this microbe transportation.

"Climatic change increases soil erosion and hurricane dynamics," Reche said. "Soil erosion—mostly in arid and semiarid regions—is increasing the exports of dust to the atmosphere and the microorganisms associated with this dust."

She continued: "Hurricanes also introduce big numbers of marine microorganisms into the troposphere."

This article has been updated to include further comment from Isabel Reche.