Answer:
1. In primary succession, newly exposed or newly formed rock is colonized by living things for the first time. In secondary succession, an area previously occupied by living things is disturbed then recolonized following the disturbance.
2. Primary and secondary succession occur after both human and natural events that cause drastic change in the makeup of an area.
3. Volcanic eruptions, Retreat of glaciers, Flooding accompanied by severe soil erosion, Landslides, Nuclear explosions, Oil spills.
