Mars rover finds signs of microbial life By Katie Franklin and agencies Last Updated: 8:53am GMT 11/12/2007 Nasa says its Mars rover Spirit has discovered "the best evidence yet" of a past habitable environment on the planet's surface. Spirit unearthed a patch of silica-rich soil Spirit has been exploring a plateau called Home Plate, where it discovered silica-rich soil in May. Researchers are now trying to determine what produced the patch of nearly pure silica - the main ingredient of window glass. They believe the deposits came from an ancient hot-spring environment or an environment called a fumarole, in which...