Answer: C. 30 - 50 million years ago
Explanation:
Fossils found in layer Y formed 30 million years ago according to the graph above. Similarly, fossils found in layer Z formed 50 million years ago.
If a fossil (fern fossil) is found between layer Y and layer Z, it means that it formed between the years that the fossils in layers Y and Z formed which is 30 - 50 million years ago.
Well If the Salmon die from lack of food from polution or something, and other animals benafit from the nutrience they carry. the rest of the ecosystem might parish, i hope that helped im not sure what was wanted
