Answer:
This shows us how old the earth is and what was around at that time and the deeper you go the deeper the fossils get.
Step-by-step explanation:
Layer A is the most recent as it is formed around the outer layer which will probably have the most recent fossils too.
Layer B is the second most recent so it probably has older fossils than layer A.
Layer C is the third most recent and has most likely extinct animals.
Layer D is the oldest and has extinct animals or old and weathered rocks inside it and is deeper than all of the other layers.
This shows us how old the earth is and what was around at that time and the deeper you go the deeper the fossils get.
Hope this helped :) have an amazing day :)