We are all planets. Is it possible for intelligent life to escape destruction, either from the planet or ourselves? Or are we destined for extinction like 99% of all species before us? Our best chance of survival may be to escape earth and build another colony somewhere else. But there are real barriers: space radiation, microgravity and the bacteria inside us will conspire against us. And our DNA is coded for the conditions here on earth, so if we ever manage to colonize another planet those who are born there will evolve into another species.

Earth's great paradox. For our planet to become inhabitable for life, you already need life. Ever since life emerged, microbes, plants and animals have all sculpted the planet's surface and air in the strangest of ways; fish poop creates islands; dead animals create mountains; lichen drive continents. But life also has the power to destroy our world. We are changing the climate, but we are not the first to do so. Long before us, microbes froze the planet and almost wiped out all life. The difference between us and them is we are conscious of our actions.

The freak accident behind complex life. All life on earth started as single cell bacteria and stayed like that for 2 billion years. Successfully spreading across the planet. So even if we do find alien life, what are the chances of that life being complex – like us? Vanishingly rare… on our strange rock, it's all down to a freak event, which accidentally happened when one cell ate another to create a kind of cellular power pack: mitochondria. This almost miraculous event transforms earth into a complex interconnected food web based on a competition for food. And at the top of the pyramid sits us humans.

Your brain is an anomaly. We tend to think that once the first life emerged it was inevitable that it would eventually evolve into us. But there is nothing inevitable about consciousness. For over 2 billion years no life on earth possessed a brain. And even today, 90% of life doesn’t have a brain. How life and our strange rock came together to create consciousness is a story of almost impossible and unnecessary coincidences….

There's no place like home. We wrap up the series with the story of NASA's most experienced female astronaut, Peggy Whitson, as she returns home to earth. We might possibly be the only intelligent life in the universe. Life is rare, complex life rarer, and intelligent life may be an evolutionary bad idea or dead end that is rarer still… and that means that it's possible that we humans may be the only thing in this huge and amazing universe that can appreciate its strangeness with awe and wonder.