"Our solar system is more than 6 billion years old. Scientists believe there was life on Mars 4 million years ago. Many people on Earth believe they are the only life forms in the universe. But, with millions of undiscovered planets out there, can that really be true? Find out how life began on Earth, how far humans have come in a short period of time, and how we might measure up to other worlds"--]cProvided by publisher.