Plot: 700 million years ago, Earth was a giant snowball cloaked in ice from pole to pole—a global deep freeze that held the planet in a stranglehold, threatening the survival of the earliest complex life. How did life manage to hold on in this forbidding world? Leading scientists investigate how this catastrophe may have become a catalyst for life to evolve in creative new ways as it bounced back from the brink—setting the stage for the astonishing complexity we see today