Is the grass poking through the cracks in a sidewalk primary or secondary succession and why?

The grass poking through the cracks in a sidewalk is an example of primary succession. This occurs when life begins to colonize a previously lifeless area, such as bare rock or disturbed soil, where no soil exists initially. In this scenario, the grass is growing in a disturbed environment where soil has developed in the cracks, indicating a progression from a barren state to one capable of supporting plant life. Secondary succession typically happens in areas that have experienced a disturbance but still retain some soil and organic matter.