Even scientists were astonished to know that millions of viruses are circulating in the atmosphere. Those viruses don't stay there, they fall on Earth.

For the first time, a scientific study has successfully analyzed the quantity of viruses being swept up from the Earth's surface and back, and it's enormous.

According to a new study by scientists from the University of British Columbia, more than 800 million viruses per square meter remain swirling in the Earth's upper troposphere. Researchers also found that billions of viruses and tens of millions of bacteria are deposited per square meter each day.

This could be the reason why genetically identical viruses can be found in very different environments in the planet. Viruses are swept from their point of origin to another environment by traveling the atmosphere.

"This preponderance of long-residence viruses traveling the atmosphere likely explains why — it's quite conceivable to have a virus swept up into the atmosphere on one continent and deposited on another," says virologist Curtis Suttle of the University of British Columbia.

Microbial Highways In the Sky

Scientists had to observe the abundance of viruses at a great height — at about 3,000 meters up high the Veleta Peak in Spain's Sierra Nevada mountain range. They gathered samples from this location that is almost the planetary boundary layer in the atmosphere that is above the weather systems but below the stratosphere. At an altitude this high, particles are likely to travel long distances unlike particles in the lower atmosphere.

Particles of soil and vapor from sea spray allow the long-range travel of viruses and bacteria, sweeping them up high in the troposphere before settling back on Earth.

Virus Rains

A previous study indicates that migration of bacteria is a natural phenomenon due to atmospheric events and ocean currents. Dust particles from deserts or arid regions can also transport microbes such as viruses and bacteria over long distances, on air currents.

Airborne microbes scattered swirling in the sky return to the Earth's surface through 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," says study author Isabel Reche, a microbial ecologist from the University of Granada.

So, when it rains, it could be literally raining viruses and bacteria.

Not Related To Flu Epidemic

It is surprising to know that there are millions of viruses in the air. Viruses are actually the most abundant microbes on the planet — if gathered all together, all viruses on Earth would cover an estimated area spanning 100 million light-years. According to the American Society for Microbiology, an estimate of 320,000 types of viruses infect mammals.

However, this raining down of viruses and bacteria phenomenon is not related to the widespread flu epidemic across the United States. The enormous viruses in the sky mostly infect only bacteria and do not mutate.

The flu virus, a type of airborne virus, can be transmitted just by breathing tiny droplets of air that are left suspended in the air. The flu virus can also mutate into different strains.

The study "Deposition rates of viruses and bacteria above the atmospheric boundary layer" is published in the journal International Society for Microbial Ecology Journal.