Geologic Time

On a geological dig, two fossil samples were found in different rock layers in the same area. One fossil was found in a rock layer that was located below the other. Which can be concluded about the relative ages of the fossils?

• The fossil found in the lower layer is older than the one found above it.
• The fossils were found in the same area, so they are the exact same age.
• The fossil found in the lower layer is younger than the one found above it.
• The fossils are differeent ages, but it cannot be determined which is older or younger.

Which are scientists most likely to use to estimate the age of Earth?

• rock layers
• soil samples
• organic fossils
• water samples

Based on the law of superposition, which best describes the ages of four undisturbed rock layers relative to one another?

• All of the layers of rock were deposited at about the same time and are about the same age.
• The youngest rock layer is found on top, and the older layers are closer to the center of Earth
• The oldest rock layer is found on top, and the younger layers are closer to the center of Earth.
• The youngest rock layer is found on the bottom, followed by the oldest layer, and then younger layers.

Why is petrified wood considered to be a fossil?

• it was once living matter.
• It is composed of hardened wood.
• It is made entirely of rock material.

Carbon 14 has a half life of 5,730 years. If a fossil sample has 25% of the original Carbon 14 in it, how old is the fossil?

• 5,730 years old
• 11,460 years old
• 17,190 years old

Which best explains the use of radioactive dating?

• to determine the presence of index fossils
• to determine the relative age of a rock layer
• to determine the absolute age of a rock layer
• to determine changes in the surface of the Earth

Which describes the best use of Carbon-14 in collecting geologic evidence?

• to compare the decay of uranium to lead
• to date artifacts less than 50,000 years old
• to date sedimentary rock layers
• to identify index fossils

Fossils were discovered in four different sedimentary rock layers as shown below: Which best describes the age of the fish relative to the age of the fern and the age of the shell?

• The fish is older than both the fern and the shell.

• The fish is younger than both the fern and the shell.

• The fish is older than the fern, but younger than the shell.

• The fish is younger than the fern, but older than the shell.

The figure below shows a wall of the Grand Canyon. The most recent rocks of the Grand Canyon formed during which Geologic Period?

• Permian

• Devorian

• Cambrian

• Precambrian

The half-life of potassium-40 is 1.3 billion years. An igneous rock is found with 25% potassium-40. What is the absolute age of this rock?

• 1.3 billion years
• 2.6 billion years
• 3.9 billion years
• 5.2 billion years