mold under carpet

https://page-wiki.win/index.php/How_to_Remove_Mold_from_Carpet:_A_Practical_Guide_for_Homeowners

When I pulled back the corner of the carpet in my basement, I was hit by a musty smell that instantly told me something was wrong. There, in the dark damp space where moisture had been trapped for years, was a patch of black mold spreading slowly across the underlay. It felt gross and alarming, knowing that every time we walked over that spot, we were probably kicking spores into the air we breathe.