Why? Because for chemical compounds to get motivated enough to turn themselves into living things, you need, among other things, standing water. And it has to be around for millions and millions of years. Curiosity has just turned up evidence that there were lakes and rivers for — guess what? — millions of years in a place called the Gale crater. Incidentally, I think it’s so cool that they named a ditch after Gale Sayres, whose records include most touchdowns in a rookie season (22 in 1965), most touchdowns in a game (6, tied with a couple of other guys), and highest career kickoff return average (30.56 yards).