What Barry Actually Wrote....
Listed at the top of http://www.icamsr.org/mars_research.html
Rock Varnish As A Habitat For Extant Life On Mars by Barry E. DiGregorio, Cardiff Centre for Astrobiology, Cardiff, UK.
Barry E. DiGregorio's 2001 SPIE Conference paper regarding rock varnish and life on Mars: from Instruments, Methods, and Missions for Astrobiology IV.
http://www.icamsr.org/docs/spie_4495-13_rock_varnish.pdf
"It is completely plausible that life developed on Mars roughly the same time period as Earth, or perhaps
even before. The early exchange of planetary debris during the late bombardment period would have
allowed viable microbial spores from the Earth to reach Mars, and vise versa."