These factors are essential for the growth and life span of the population of species in an ecosystem. The larger the space, the more light it obtains, and the more food the area produces; the larger the population of species in an ecosystem. having less space, light, and food, the results would be vice versa.
I think the answer is "the older it is"
Reason: I might be wrong but is something (like a shell) gets buried in something (like sand), overtime many things (like dirt, soil, sand, etc.) will be on top of the original. This will make layers. So, the older rock is on the bottom since it has been there for the longest and it gets covered by other stuff (causing the layers).
Hope this helps! :) (If I'm wrong, sorry :( )
I believe it would be sperm
Spermatogonia is my answer
