Today I close out a month-long guest blog over at the University of Chicago Press to mark the publication of my book A Planet of Viruses. I've been talking with experts about some of the most thought-provoking areas of virus research-- 1. Can viruses control our minds? 2. Should we eliminate smallpox? 3. How can we use viruses to cure disease? Today I talk with Penny Chisholm of MIT about the viruses that fill the worlds oceans (a billion in every spoonful). They kill off half the bacteria in the ocean every day, dumping out carbon and having enormous ecological effects--and perhaps even effects on the planet's climate. Chisholm and I speculate on whether we could use viruses to manipulate the planet as a whole. It's extreme speculation to be sure--but, then again, when it comes to viruses, the truth can sometimes seem too fantastic to be real. Check it out!