We thought he was joking at first, but then we realized that he was 'in earnest'. [=he was being serious]
It's hard to tell if he's making this proposal 'in earnest'.
It began to rain 'in earnest' [='heavily'] in the evening.
(..) except how great she is at her job. I'm sorry. I can't- - I can't believe this. You're defending her? - Yeah. The wide-eyed girl peddling her earnest newspaper stories? You, my friend, are crossing over to the dark side. I resent that. - You shouldn't. It's sexy. - Sexy? (..)2006 The Devil Wears Prada