An area of exposed rock after a glacier melts away
Step-by-step explanation:
Primary succession involved the colonization of a new rock substrate by living things. Usually for the first time while in secondary succession involved recolonization after the first ecosystem was decimated by some form of disaster.
When the glacier melts away it exposes new rock substrate underneath it. This rock will begin by being colonized by lower plants like lichen and moss. They break down the rock into shallow soil enabling higher plants with shallow roots to colonize. This further releases the nutrients in the soil and causes the soil to be deep. Eventually, trees, that form part of the climax community will be also to be supported in the new environment.