I think there has been due diligence in asking the question "Did Mars have a significant period in it's history that it could have been habitable?". The answer

I think there has been due diligence in asking the question "Did Mars have a significant period in it's history that it could have been habitable?". The answer to that question is "yes"; data suggest that Mars had a significant wet period. There are no bounds on what we might find if we can scrape a way the first few feet of sediment.