There are about 10 times as many viruses in the oceans as there are bacteria and about 1000-fold less protists than bacteria. In fact, in a litre of coastal seawater there are more viruses than there are people on the planet. If one takes a drop of seawater and adds a nucleic-acid stain such as Yo-Pro, SYBR Green, or SYBR Gold and looks at it under a microscope, there are a myriad of tiny fluorescent dots that are reminiscent of a clear night sky (Fig. 1). Most of these dots are virus particles. If aliens randomly sampled Earth they would see a planet dominated by microbial life, most of which would be viruses. On average, there are about 10 million viruses and a mil- lion bacteria per litre of seawater or freshwater. If we compare the number of viruses in the oceans to the number of stars in the universe, there are about 1023 stars in the universe. In contrast, there are about 10 million-fold more viruses in the ocean than there are stars in the universe. If we took the 1030 viruses in the oceans and stretched them end-to-end, how far would they go? Assuming, the average length of a virus is about 100 nm, the viruses would stretch 1023 m, which is 1020 km. If converted to light years, by dividing by 1013 km, we end up with 10 million light years. The nearest star is Proxima Centauri, about 4.2 light years away; the Crab Supernova is 1000 light years away; our own gal- axy, the Milky Way, is about 150 000 light years across. In fact, all the viruses in the ocean end-to-end would stretch further than the nearest 60 galaxies. This may seem like a trivial calculation, but it is important on a number of levels. For one reason, these viruses are responsible for about Avogadro’s number, about 1024 infec- tions per second in the ocean. Each one of these events is an opportunity for lateral transfer of genes. Most of the genetic information on Earth probably resides within viruses.