We all believe that viruses are the scourge of mankind, their very mention reminds us of illness and death. But viruses are probably the most misunderstood things on earth, taxonomist are unsure if they are even living or non-living. A few of the millions of species of viruses that exist on earth give them a bad name. Viruses have saved more people than killed them. Marine viruses are the most infectious viruses of all, not to humans but to microbes in water. Every day, about half the bacteria in the world’s oceans are killed by them and humans indeed benefit from their deadliness. Cholera is caused by blooms of waterborne bacteria called Vibrio. But Vibrio are host to a number of phages (virus that infect bacteria). When the population of vibrio explodes, it causes a cholera epidemic. But this explosion also results in the multiplication of phages. The phage population rises so quickly that it kills the Vibrio faster than the microbes can reproduce. The bacterial boom subsides and the cholera epidemic fades away. A large amount of the oxygen we breathe is also a gift from viruses. An ocean bacterium called Synechococcus, carries out about a quarter of the worlds photosynthesis. The protein that carries out the light harvesting is actually from a virus. Scientists have even found free-floating viruses with photosynthesis genes, searching new hosts to infect. For every 10 breath you breathe, one of those breaths comes courtesy of viruses. Viruses also control the temperature on earth. Algae and photosynthetic bacteria churn out half our oxygen supply. Algae also release a gas called dimethyl sulphide that rises into the air and seeds clouds. These clouds reflect incoming sunlight back into outer space cooling the planet. The viruses check the algae growth and that keeps our planets thermostat at the right temperature. As you just read, viruses have earned a bad reputation, but they contribute more to life than we appreciate.