Posted by tourdemars to Life on Mars at December 11, 2007 04:41 PM

Nasa says its Mars rover Spirit has discovered "the best evidence yet" of a past habitable environment on the planet's surface. 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 acidic steam rises through cracks. On Earth, both of these types of settings teem with microbial life, said rover chief scientist Steve Squyres.