A group of researchers say NASA scientists have failed to prove their contention that a Mars meteorite contains evidence of ancient microbial life on the Red Planet. A group led by Peter Buseck of Arizona State University said the NASA researchers have inadequate evidence showing that tiny crystalline structures in Mars meteorite ALH84001 were formed by bacteria billions of years ago as the rock was sitting on the Martian surface. A study with Buseck as the first author appears today in the Proceedings of the National Academy of Sciences.