In message , Les Hemmings
writes

http://news.bbc.co.uk/1/hi/help/3681938.stm

Press briefing live now... Gully formed recently (not 6 million years, 6
months!)

Six months? Sometime in the last seven years, I gather.
But isn't there a suggestion that the gullies are formed by carbon
dioxide
http://unisci.com/stories/20012/0402013.htm
http://adsabs.harvard.edu/abs/2002AsBio...2..313H