M. H. Carr 1996 The Martian surface shows abundant evidence of water erosion. Liquid water is unstable under present climatic conditions but conditions may have been different in the past. The planet has been volcanically active throughout its history. The combination of water and volcanism must have commonly resulted in hydrothermal environments similar to those in which grow the most primitive terrestrial life-forms. application/pdf 10.1016/0160-9327(96)10013-2 en Water erosion on mars and its biologic implications article