Sagan discusses comets and asteroids as planetary impactors, giving recent examples of the Tunguska event and a lunar impact described by Canterbury monks in 1178. It moves to a description of the environment of Venus, from the previous fantastic theories of people such as Immanuel Velikovsky to the information gained by the Venera landers and its implications for Earth's greenhouse effect. The Cosmos Update highlights the connection to global warming.

The episode, devoted to the planet Mars, begins with scientific and fictional speculation about the Red Planet during the late nineteenth and early twentieth centuries (H. G. Wells' The War of the Worlds, Edgar Rice Burroughs' science fiction books, and Percival Lowell's false vision of canals on Mars). It then moves to Robert Goddard's early experiments in rocket-building, inspired by reading science fiction, and the work by Mars probes, including the Viking, searching for life on Mars. The episode ends with the possibility of the terraforming and colonization of Mars and a Cosmos Update on the relevance of Mars' environment to Earth's and the possibility of a manned mission to Mars.

Sagan reflects on the future of humanity and the question of 'who speaks for Earth?' when meeting extraterrestrials. He discusses the very different meetings of the Tlingit people and explorer Jean-François de La Perouse with the destruction of the Aztecs by Spanish conquistadors, the looming threat of nuclear warfare, and the threats shown by destruction of the Library of Alexandria and the murder of Hypatia. The episode ends with an overview of the beginning of the universe, the evolution of life, and the accomplishments of humanity and makes a plea to mankind to cherish life and continue its journey in the cosmos. The Cosmos Update notes the preliminary reconnaissance of planets with spacecraft, the fall of the Berlin Wall and the end of apartheid in South Africa, and measures towards the reduction of nuclear weapons.

Dinosaurs ruled the earth for 150 million years, then suddenly they were gone. Their disappearance is one of the planet’s greatest mysteries – unimaginable, until now. The film proposes a minute-by-minute chronology of the Chicxulub impact and its effect on the dinosaurs and other animals around the world. A blow-by-blow account of the cataclysm that ended the reign of the dinosaurs, and forever changed the course of life on Earth.

Discoveries of new planets have revealed countless worlds much stranger than Earth. Some of these strange worlds don’t have stars; others are made out of diamonds. Will we ever find a planet like Earth, or are these distant worlds stranger than fiction?

Global warming, and how to combat it, has provoked intense debate, changed the way we see the planet and created headlines around the world. But when and how did scientists first discover global warming, why has it led to such furious debate? In this three-part series geologist Dr Iain Stewart presents a definitive guide to the history of climate change.
Battle Begins uncovers some of the great unsung heroes of climate change science, and introduces us to a secret organisation of American government scientists, known as Jason, who wrote the first official report on global warming as far back as 1979. By the late 1980s global warming had already become a serious political issue. It looked as if the world was uniting to take action. But it turned out to be a false dawn.