Primary succession is when, for example, a volcano explodes and there is nothing left and even the soil is ruined. It would take at least a hundred years for the land to be like it was before the volcano erupted. Secondary succession is when, for example, a wild fire happens but the soil is not ruined. It would take at least 25-50 years for the land to be like it was before the fire.
Just think about cancer.. it's uncontrolled cell growth, so mutations in genes can cause cancer by accelerating cell division. As the cells contribute to grow they then develop as a tumor.
