Our tale of two planets begins four billion years ago. One planet was Earth, and the other planet was Mars, and the two had much in common in their infancy. Rivers and lakes etched their surfaces, craters pockmarked their faces, and volcanoes rose from their plains. But something seems to have changed on one and not the other.
In Earth’s burbling warm water, fate and chemistry combined amino acids into complex molecules, and in a process we still don’t understand, these gave rise to single cells that figured out how to make copies of themselves. Tiny mistakes in those copies eventually turned them into oxygen-exhaling organisms we call algae. Endless forms flowed from these humble ancestors, and after eons, there we were: All of human culture and hope and possibility arising within a tiny slice of time.