Dr. Sagan's cosmic calendar makes the history of the universe understandable and frames the origin of the Earth and the evolution of life. We see the evolutionary process unfold, from microbes to humans. Our understanding of how life developed on Earth enables us to venture to other worlds for imaginative speculations on what forms life might take elsewhere.

A descent through the hellish atmosphere of Venus to explore its broiling surface serves as a warning to our world about the possible consequences of the increasing greenhouse effect. Then Dr. Sagan leads us on a tour of our solar system to see how other heavenly bodies have suffered from various cosmic catastrophes.