. . . . . . . "\"The early Earth was a much different planet than the one we know today. Ancient rocks provide evidence of the emergence of oxygen in the atmosphere and of a frozen Snowball Earth. Scientists Paul Hoffman and Andrew Knoll look at these clues to help explain the rise of complex animal life.\" --cover." . . . "The habitable planet many planets one Earth" . . . . . . . . . . "Many planets one Earth" .