Geologic Time Scale

Question

The geologic time scale goes back 4.6 billion years. During that time, we have used fossil records to piece together the history of life on Earth as well as other events, such as climate changes and plate movements. Studying the fossils found in different rock layers can tell us which organisms existed together and in what order they lived.
Two fossils found in the rock layers are shown.

Fossil 1 is a horseshoe crab fossil. Fossil 2 is a trilobite fossil.

Which explanation best applies the rock layer phenomena to the relative age of these fossils?

A.
The relative age of the organisms from Fossils 1 or 2 cannot be determined because the rock layers are different.

B.
Fossil 1 is from an older organism than Fossil 2 because it appears in more than one rock layer.

C.
Fossil 2 is from an older organism than Fossil 1 because it first appears in a lower rock layer.

D.
Fossils 1 and 2 are from organisms that lived at the same time because they appear in similar rock layers.

Answer 1

The best explanation that applies the rock layer phenomena to the relative age of these fossils is:

C. Fossil 2 is from an older organism than Fossil 1 because it first appears in a lower rock layer.

In geology, the Law of Superposition states that in undisturbed strata, the oldest layers are at the bottom and the youngest are at the top. If Fossil 2 (the trilobite fossil) is found in a lower rock layer than Fossil 1 (the horseshoe crab fossil), it indicates that trilobites existed before horseshoe crabs, illustrating the principle of relative dating based on rock layers.