Tiny mole on bottom of foot. never been there before and just popped up. serious?

Hard to say....: The problem with these darkened lesions that just pop up is, that you can never really be sure as to the type until it is removed. I recommend taking a picture of it and comparing it to a picture taken in a month or two. The next time you see your doctor, show him/her the mole and see if it warrants further treatment. Of course, if there is any doubt, cut it out.