Which of the following is richest in fossils?

What does the study of fossils in different sedimentary layers indicate?

$A$: Similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry.
$R$: All groups of vertebrates arise from a common ancestor with great adaptation capability.

The ratio of $^{14}C : ^{12}C$ in a fossil bone is $(1/16)$ of that in a living animal bone. If the half-life of $^{14}C$ is $5730$ years, then the age of the fossil bone is: (in $years$)

Fossils are studied for:

Ammonites are fossil shell remains of