Question 1

Which of the following best describes the principle of radiometric dating used to determine the age of rocks and fossils?

Accepted Answer

It calculates the age of a rock based on the decay of radioactive isotopes, using the formula $$N_t = N_0$ e$$^{-\lambda t}$$, where N_t$ is the number of parent isotopes remaining, N_0$ is the original number, $$\lambda$$ is the decay constant, and t$ is time.

Question 2

A fossil is found in a rock layer that contains 25% of its original radioactive isotope. If the half-life of the isotope is 10 million years, how old is the fossil?

Accepted Answer

$$20$$ million years

Question 3

Which of the following statements about the fossil record is correct?

Accepted Answer

The fossil record is biased toward organisms with hard parts and those that lived in environments conducive to fossilization.

Question 4

Which event marks the boundary between the Paleozoic and Mesozoic eras in the geologic record?

Accepted Answer

The mass extinction at the end of the Permian period

Question 5

A paleontologist discovers a fossil in a sedimentary rock layer above a layer dated to 150 million years ago and below a layer dated to 100 million years ago. What is the most accurate age range for the fossil?

Accepted Answer

Between 100 and 150 million years old

Question 6

Which of the following best explains why the fossil record is considered incomplete?

Accepted Answer

Most organisms decompose before they can be fossilized, and geological processes can destroy fossils.

Question 7

Which of the following evolutionary transitions is best documented by the fossil record, as shown in the provided materials?

Accepted Answer

The transition from synapsid reptiles to mammals

Question 8

If a radioactive isotope has a half-life of 4.5 billion years, how much of the original isotope remains after 9 billion years?

Accepted Answer

$$\frac{1}{4}$$

Question 9

Which of the following is a key event in the history of life that occurred during the Proterozoic eon?

Accepted Answer

The origin of multicellular eukaryotes

Question 10

A scientist is using the ratio of parent to daughter isotopes in a rock to determine its age. Which equation should they use to calculate the age of the rock?

Accepted Answer

$$t = \frac{1}{\lambda} \ln \left( \frac{N_0$}{N_t} \right)$$

Question 11

Which of the following best describes the significance of the Cambrian explosion?

Accepted Answer

It represents a rapid diversification of animal body plans and the appearance of most major animal phyla.

Question 12

Which of the following is NOT a method used to date rocks and fossils?

Accepted Answer

Counting the number of sedimentary layers

Question 13

Which of the following statements about the geologic time scale is correct?

Accepted Answer

Periods are subdivided into epochs.

Question 14

Which anatomical change is most significant in the transition from early synapsids to mammals, as shown in the fossil record?

Accepted Answer

Development of a single lower jaw bone (dentary)

Question 15

Why are index fossils useful for correlating the ages of rock layers in different geographic locations?

Accepted Answer

They are widespread, abundant, and existed for a relatively short geologic time span.

The Fossil Record, Geologic Time, and the Origin of Mammals

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