Are you ready for serious Jimmy Fallon? Serious Jimmy Fallon is ready for you. For Monday night’s show, the Tonight Show host filmed himself singing an extremely reverent version of David Bowie’s “Life on Mars?” alongside Coldplay’s Chris Martin, the most reverent man in show business. Is this liltingly Bowie-like performance a tribute? An impression? An audition for some unknown biopic? Either way, after Vinyl and Girls Sunday night, it’s clear we’re living in a second golden age of “Life on Mars?” on TV; the first, of course, was from October 2008 to April 2009, when Jason O’Mara, Harvey Keitel, and Michael Imperioli thrilled audiences for 17 weeks on ABC.