Is Earth exceptional? : the quest for cosmic life

"For a long time, scientists have wondered how life has emerged from inanimate chemistry, and whether Earth is the only place where it exists. Charles Darwin speculated about life on Earth beginning in a warm little pond. Some of his contemporaries believed that life existed on Mars. It once seemed inevitable that the truth would be known by now. It is not. For more than a century, the origins and extent of life have remained shrouded in mystery....