Go with your gut and learn from mistakes.
The fossil range can simply be defined as the time period in which an organism has existed, thus left fossil traces of its existence. The fossil range can be very short, medium, or long, thus usually there are limitations before certain type of organism evolves into another species, thus eliminating the ancestral organism from the fossil records. On the other hand, there are organisms that have incredibly big fossil ranges of several hundred million years, and since they emerged, they have remained almost unchanged. Those kind of fossil ranges are very rare though, and they don't represent the general picture. Most of the fossil ranges are between several thousand years and several million years, as that is usually how much a species exists, ending its reign, be it because of competition, changes in the environment, or big natural disaster.
A. Silt is no longer carried down river.
Primary succession occurs when new land is formed or bare rock is exposed
this question seems to be missing some key information.
