Mars has always been a provocateur. The planet has a long history of making us uneasy, from the portents of violence our ancestors associated with its red glow, to our science-fiction nightmares of malicious, technologically superior alien invaders. And Mars is still stirring things up in the scientific community. For several years now, there has been an on-going debate as to whether a meteorite from Mars contains the fossilized remnants of microbial life. Some scientists think we no longer have to wonder about whether there is other life in the universe; we have the remains of tiny Martian cousins in our laboratories at this very moment. Others remain skeptical, claiming that every structure and chemical in the meteorite could have been formed by natural processes that have nothing to do with life, like chemical weathering and heating. Despite the controversy, the Martian Meteorite debate has already taught us a lot about what kind of questions to ask the next time we get our hands on a sample of Martian soil, as well as shown us how little we understand about the threshold of life itself.