Step-by-step explanation:
The problem here deals with relative dating of fossils in a stratigraphic column.
To solve this problem, we apply one of the rules of interpreting a session which is the principle of fossil and fauna succession:
"fossils and fauna in a geologic sequence succeed one another in a predictable way".
The oldest fossil is found in the oldest bed usually at the bottom of the sequence.
The youngest fossil is found at the top of the beds.
1. Oldest organism in the sequence;
Trilobite
2. Organism in the youngest layer;
Fern
3. Older organism between Crinoid and Ammonite;
Ammonite
The ammonite is below the crinoid in the sequence.