This document contains 27 multiple choice questions about radioactive dating and Earth's geologic history. The questions assess understanding of key concepts such as radioactive decay, index fossils, stratigraphy, and the geologic time scale. Correct answers require applying principles of radioactive dating using carbon-14 or interpreting rock layers and fossils to deduce relative and absolute ages.

1. A) life has not changed significantly throughout
Earth’s history
B) life has evolved from complex to simple forms
C) many organisms that lived on Earth have become
extinct
D) mammals developed early in the Precambrian time
period
1. Based on fossil evidence, most scientists infer that
A) addition of free oxygen to Earth’s atmosphere
B) formation of clastic sedimentary rocks
C) movement of tectonic plates
D) filling of the oceans by precipitation
2. Which event in Earth’s history was dependent on the
development of a certain type of life-form?

2. A) B)
C) D)
3. Which time line most accurately indicates when this sequence of events in earth's history occurred?

3. 4. The time line below represents the geologic history of Earth. Letters A, B, C, and D represent specific times
in Earth’s history.
A) A B) B C) C D) D
Which letter best indicates when trilobites became extinct?
A) B)
C) D)
5. Which bedrock drill core contains fossils of the life-form
that lived earliest in the Earth's history?
A) index fossils B) cementing agent
C) texture D) color
6. Which bedrock feature is most useful in correlating
sedimentary bedrock in one area with sedimentary
bedrock in another area?
A)
B)
C)
D)
7. Which pair of index fossils can be found in Ordovician
bedrock?

4. A) B)
C) D)
8. Which sequence of New York State index fossils shows the order in which the organisms appeared on
Earth?
9. Base your answer to the following question on the geologic cross section below. The cross section shows
Vermont index fossils in rock layers that have not been overturned. Rock unit A is an igneous intrusion and
line XY represents an unconformity.
Based on fossil evidence, determine the geologic period during which the unconformity formed.

5. 10. Base your answer to the following question on the cross sections below, which show widely separated
outcrops labeled I, II, and III. Index fossils are found in some of the rock layers in the three outcrops. In
outcrop III, layers A, B, C, and D are labeled. Line XY represents an unconformity. Line GH represents a
fault.
On outcrop II below, place the symbol ~~ for an unconformity between the two rock layers where the
Silurian-age bedrock has been removed by erosion.

6. 11. Base your answer to the following question on The
three geologic columns below represent the rock layers
in outcrops located several miles apart. The rock layers
have not been overturned. Two different index fossils
are shown.
A) B)
C) D)
Of the rock layers found in these three outcrops, which
layer was probably formed most recently?
A) carbon-14 B) potassium-40
C) uranium-238 D) rubidium-87
12. Which radioactive element would be best for
determining the age of a 25,000-year-old rock sample
containing organic remains?
A) Carbon-14 has a relatively short half-life and too
little carbon-14 is left after 50,000 years.
B) Carbon-14 has a relatively long half-life and not
enough carbon-14 has decayed after 50,000 years.
C) Carbon-14 has been introduced as an impurity in
most materials older than 50,000 years.
D) Carbon-14 has only existed on Earth during the
last 50,000 years.
13. Why is carbon-14 not usually used to accurately date
objects more than 50,000 years old?
A) carbon-14 B) potassium-40
C) rubidium-87 D) uranium-238
14. Which radioactive substance has the longest half-life?

7. 15. Base your answer to the following question on the diagram below, which represents a model of a
radioactive sample with a half-life of 5000 years. The white boxes represent undecayed radioactive
material and the shaded boxes represent the decayed material after the first half-life.
A) carbon-14 B) potassium-40 C) uranium-238 D) rubidium-87
Which radioactive isotope has a half-life closest in duration to this radioactive sample?
A) 1,400 years B) 2,800 years
C) 5,600 years D) 11,200 years
16. A geologist uses carbon-14 to determine the age of a
sample of material found in a sedimentary deposit. If
the sample shows that 50 percent of the original
carbon-14 is left, what is the approximate age of the
sample?
A) 1/8 g B) 1/16 g
C) 1/32 g D) 1/64 g
17. The table below gives information about the radioactive
decay of carbon-14. [Part of the table has been left
blank for student use.]
What is the amount of the original carbon-14 remaining
after 34,200 years?
A) 2,850 years B) 5,700 years
C) 11,400 years D) 17,100 years
18. A sample of wood that originally contained 100 grams
of carbon-14 now contains only 25 grams of carbon-14.
Approximately how many years ago was this sample
part of a living tree?

8. A) 5,700 years B) 17,100 years
C) 22,800 years D) 28,500 years
19. How old is a fossil that has radioactively decayed
through 4 half-lives of carbon-14?
A) 2,800 years B) 5,700 years
C) 11,400 years D) 17,100 years
20. A sample of wood found in an ancient tomb contains
25% of its original carbon-14. The age of this wood
sample is approximately
21. Base your answer to the following question on the diagram below, which represents a model of the
radioactive decay of a particular element. The diagram shows the decay of a radioactive element into the
stable decay element after one half-life period.
If the radioactive element in this model is carbon-14, how much time will have passed after one half-life?
A) B)
C) D)
22. Which graph best shows the radioactive decay of
carbon-14?
A) 0% B) 25% C) 50% D) 75%
23. Radioactive carbon-14 dating has determined that a
fossil is 5.7 × 103 years old. What is the total amount of
the original Cl4 still present in the fossil?
A) 1,400 years B) 2,800 years
C) 5,600 years D) 11,000 years
24. An ancient bone was analyzed and found to contain
carbon-14 that had decayed for nearly two half-lives.
Approximately how old is the bone?

9. 25. The diagram below shows the relative proportions of
carbon-14 (C-14) to nitrogen-14 (N-14) in a rock.
A) 2.85 × 103 B) 5.7 × 103
C) 1.3 × 109 D) 4.5 × 109
What is the most likely age of the rock?
26. Base your answer to the following question on the date table below, which shows the radioactive decay of
carbon-14. The number of years required to complete four half-lives has been left blank.
How long does it take for radioactive carbon-14 to complete four half-lives?

10. 27. The table below shows information about the
radioactive decay of carbon-14.
A) g B) g C) g D) g
What is the amount of carbon-14 remaining after 28,500
years?
28. The table below gives information about the radioactive
decay of carbon-14. [Part of the table has been left
blank for student use.]
A) g B) g C) g D) g
What is the amount of the original carbon-14 remaining
after 34,200 years?