In 1996 NASA officials called a news conference to announce that a meteorite from Mars found in Antarctica in 1984 was discovered to contain organic compounds, minerals, and "carbon globules"—all of which indicate the presence of bacterial life on Mars. They also speculated that wormlike structures seen by electron micro-scopes could be the fossil remains of Martian microorganisms born billions of years ago, when Mars was warmer and wetter. If the evidence was correctly interpreted, it could mean that life existed on Mars and might possibly be found on other planets as well. The announcement made banner headlines. The evidence presented by NASA, however, came under attack from many experts. A UCLA specialist on ancient bacteria said it was unlikely that the findings proved bacterial life. In 1998 three papers on meteors were published suggesting that the same features were found in lunar meteorites and...