Okay, never mind that what may have been humankind's first encounter with extraterrestrial life didn't have the drama ofThe War of the Worlds, independence Dayor evenMy Favorite Martian. Never mind that toy companies are now trying to figure out how to bid for the rights to and then market toys patterned after submicrometer‐long extraterrestrial bacteria. What is important is for us to understand the chain of scientific reasoning that has led to the claim that the Allan Hills (ALH) 84001 meteorite may contain fossil evidence of life from Mars.