We tend to think of viruses as things that make us sick. That's true, but there's another, less-obvious purpose that virus serve: they indirectly help to promote life on this planet. According to University of Warwick Professor Nicholas Mann, some of the oxygen that we breathe is a by-product of viral action.

This is how it works: reportedly half of the world's oxygen is produced by cyanobacteria living in tiny photosynthesizing creatures called phytoplankton. Mann explained that these bacteria also lock away carbon dioxide.

The interesting thing is that the cyanobacteria serve are targeted by a range of different types of viruses. Mann and his colleagues discovered that some of the viruses provide the genetic material that code for key components of the photosynthesis process.

It's ironic, indeed, that we may partly owe our continued existence to bacteria suffering from viral infections. Still, it provides a different perspective on how something we normally shun can serve a hidden and greater purpose. As Mann put it:

Instead of being viewed solely as evolutionary bad guys, causing diseases, viruses appear to be of central importance in the planetary process. In fact they may be essential to our survival.