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Ecological succession is the observed changes that occur over time in a geographical area. There are two types of succession that can occur
Secondary succession occurs when all life and soil have been stripped from the land, An example is when volcano erupts and pioneer species must appear to break down the rocks into soil.
Primary succession occurs when there has been a disruption to the land, but the soil and some life are largely intact. An example is when a farmer clears a forest to graze cattle. Eventually succession reaches a point called climax community in which the population of organisms remain stable and exist balance with each other. This equilibrium requires that each species of organism contain its own place to live or habitat. The second requirement is that each species of organism have its own functional role or niche

Crust,mantle,core,earth