On paper, putting “Life On Mars” on after “Lost” seemed like a good idea. But if the first week is an indicator, it could be a killer for the cop time travel series. “Life On Mars” earned a 4.0 rating/7 share on ABC Wednesday night, according to Fast National Ratings from Nielsen Media Research. That was down more than 25 percent from the last time it aired a new episode just before Thanksgiving, when ABC was still airing it against “Eleventh Hour” on Thursday nights. But the new Wednesday slot was not so busy. In fact, “Mars” only had to compete with a rerun of “CSI: NY” as well as a new episode of “Law & Order” on NBC, both of which beat “Mars” handedly. “Law & Order” drew a 48 percent larger audience than “Life On Mars” despite having a rerun as a lead-in. “Mars” can’t …