Question

read the passage and answer the following question(s).
determining earths geologic time scale
the geologic time scale is a system that scientists use to separate intervals of time in earths 4.5 - billion - year - old history. the time scale was formed by determining the composition, sequence, and relative age of rock layers. these data, combined with information provided by fossils, gave scientists an understanding of major events in earths history such as mountain formation, the first appearance of mammals, and major extinction events. today, scientists all over the world use the same sets of geologic rules and principles to determine rock relationships. scientists continue to combine rock and fossil data to better understand earths geological history.
index fossils are widely distributed fossils of organisms that lived only during one period of time. the picture shows index fossils that were collected from two locations.
which statement best compares the ages of the rock found at layer 7 in utah to layer 5 in texas?
a. the rock layers in both locations are the same age because they contain the same type of fossils
b. layer 7 in utah is older than layer 5 in texas because it has more layers on top of it
c. the rock layers in both locations are the same age because they are both made of sedimentary rock
d. layer 7 in utah is younger than layer 5 in texas because it has fewer layers below it

Explanation:

Step1: Understand index fossils

Index fossils are of organisms that lived only during one period of time. If two rock layers have the same index fossils, they are from the same time period.

Step2: Analyze each option

• Option A:

Since the rock layers (Layer 7 in Utah and Layer 5 in Texas) have the same index fossils (as per the diagram), they are of the same age.

• Option B:

The number of layers on top does not determine the age relationship when index fossils are present. Index fossils are key for age - determination here.

• Option C:

Just being sedimentary rock does not mean they are of the same age. Index fossils are a more specific indicator.

• Option D:

The number of layers below is not relevant when index fossils can be used for age - correlation.

Answer:

A. The rock layers in both locations are the same age because they contain the same type of fossils