What does the principle of faunal succession state? Fossils are deposited in approximately horizontal layers and spread out until they reach a barrier.

Absolute dating is required to determine the relative age of animals based on their fossils.

Specific groups of organisms have followed one another in a definite sequence through the Earth's history.

Rock layers with the same unique grouping of fossils are of the same geologic age.

The answer is A. Fossils are deposited in approximately horizontal layers and spread out until they reach a barrier.