Rock Record Quiz
NYS Earth Science Regents Review
Geologic History Diagnostic
Score: ______ / 30 pts
STUDENT NAME:
DATE:
CLASS PERIOD:
Part A: Multiple Choice (12 points). Answer all questions in this section by writing the number of the best response (1, 2, 3, or 4) in the answer blank provided to the left of each question. Use your knowledge of earth science and the Earth Science Reference Tables (ESRT) where applicable.
Which characteristic of a fossil isotope makes it most useful for determining the absolute age of a very old rock layer?
(1) a short half-life and chemical reactivity
(2) a short half-life and organic stability
(3) a long half-life and predictable rate of decay
(4) a long half-life and resistance to heat and pressure
Why is Carbon-14 (\(^{14}\text{C}\)) radioactive isotope not used to determine the age of trilobite fossils found in Cambrian bedrock?
(1) Cambrian bedrock has been completely melted.
(2) Carbon-14 has a half-life that is too short.
(3) Trilobites did not absorb Carbon-14 when alive.
(4) Carbon-14 decay rate changes with depth.
To be classified as an excellent index fossil, an organism must have existed over a:
(1) narrow geographic area for a short geologic time
(2) narrow geographic area for a long geologic time
(3) wide geographic area for a short geologic time
(4) wide geographic area for a long geologic time
The diagram below represents a timeline of Earth's history. Letters A, B, C, and D represent specific geologic time intervals.
4.6 Billion Years Ago (Origin of Earth) Present Day
A
B
C
D
In which of these intervals did the dinosaurs dominate and subsequently go extinct?
(1) Interval A
(2) Interval B
(3) Interval C
(4) Interval D
NYS Earth Science Regents Diagnostic: Geologic History Page 1 of 3
Part A (Continued) & Part B-1
An unconformity in the rock record represents a significant gap in geologic time. Which sequence of events best describes the formation of an unconformity?
(1) Uplift → Erosion → Subsidence → Deposition
(2) Deposition → Melting → Intrusion → Folding
(3) Erosion → Faulting → Folding → Metamorphism
(4) Subsidence → Intrusion → Uplift → Erosion
If an original sample of radioactive Uranium-238 decayed until only 12.5% of the parent material remained, how many half-lives have elapsed?
(1) 1 half-life
(2) 2 half-lives
(3) 3 half-lives
(4) 4 half-lives
Part B-1: Geologic Cross-Section Analysis (10 points). Analyze the geological cross-section below, which shows folding, faulting, an igneous intrusion, and an unconformity. Answer questions 7 through 10 in the blank answer spaces provided.
Intrusion H F F' Layer A (Siltstone) Layer B (Limestone) Layer C (Sandstone) Layer D (Shale) Unconformity X-Y
7. Identify the relative age relationship between Intrusion H and Layer C. Explain your reasoning using a specific geologic principle. [2 pts]
8. Explain how the graphic evidence demonstrates that Fault F-F' is older than Unconformity X-Y. [2 pts]
9. List the chronological order of the following events from OLDEST to NEWEST: Deposition of Layer B, Intrusion H, Folding of Layer D, Faulting F-F'. [2 pts]
Oldest: → → → Newest:
NYS Earth Science Regents Diagnostic: Geologic History Page 2 of 3
Part B-2: Isotopes & Index Fossils
Part B-2: Radioactive Decay and Correlation (8 points). Below is a standardized radioactive decay curve for an isotope used in dating geologic formations. Use this graph and the reference information to answer questions 10 through 13.
Radioactive Decay Curve
100% 75% 50% 25% 0% 0 1 HL 2 HL 3 HL 4 HL
Number of Half-Lives elapsed
Parent Material Remaining (%)
| Isotope Pair | Half-life (yrs) |
|---|
| Carbon-14 → Nitrogen-14 | 5,700 |
| Potassium-40 → Argon-40 | 1.3 billion |
| Uranium-238 → Lead-206 | 4.5 billion |
| Rubidium-87 → Strontium-87 | 49 billion |
10. A fossilized bone contains 25% of its original Carbon-14. Calculate the absolute age of the fossil in years. Show your work. [2 pts]
11. State why Rubidium-87 is an inappropriate isotope for dating human artifacts from the last Ice Age (approx. 12,000 years ago). [2 pts]
12. A volcanic ash layer contains Potassium-40 crystals. If the rock is determined to be 3.9 billion years old, state the ratio of parent Potassium-40 to daughter Argon-40 remaining in the crystals. [2 pts]
13. Explain why index fossils like Phacops (a Devonian trilobite) are found in sedimentary rock layers but never in igneous rock formations. [2 pts]
NYS Earth Science Regents Diagnostic: Geologic History Page 3 of 3
Rock Record Answer Key
Teacher Grading Guide & Explanations
Rock Record Answer Key
Total: 30 Points
PART A (MC) 6 Questions • 2 pts each 12 Points Total
PART B-1 (Sec.) 3 Questions • 2 pts each 10 Points Total
PART B-2 (Decay) 4 Questions • 2 pts each 8 Points Total
Part A: Multiple Choice Analysis
Question 1: Absolute Age Determination Correct Choice: (3)
Explanation: To date older rock layers (such as Precambrian or Paleozoic), we need an isotope with a long half-life (like Uranium-238 or Potassium-40). The decay rate of a radioactive isotope is constant and unaffected by external environmental factors, making it highly predictable.
Teacher Note: Remind students that half-life is entirely independent of temperature, pressure, and sample size.
Question 2: Carbon-14 Dating Limits Correct Choice: (2)
Explanation: Carbon-14 has a very short half-life of 5,700 years. After about 50,000 to 70,000 years, there is not enough parent Carbon-14 left to measure accurately. Trilobites are from the Paleozoic Era (Cambrian Period), hundreds of millions of years ago, making Carbon-14 completely obsolete.
Question 3: Index Fossil Criteria Correct Choice: (3)
Explanation: An ideal index fossil must be geographically widespread (found in many locations globally to allow correlation across oceans and continents) and have lived for a short, specific duration of geologic time (so it identifies a precise, narrow geologic boundary).
Question 4: Timeline Interpretation Correct Choice: (3)
Explanation: The Mesozoic Era (the age of dinosaurs) occurred from 251.9 million to 66 million years ago. On the timeline, Interval C represents the Phanerozoic eon's middle-to-recent sections. Looking closely at the sizes: Precambrian takes up ~88% of Earth's timeline (Interval A and B). Paleozoic/Mesozoic is Interval C, and Cenozoic (present day) is Interval D.
Q5: Unconformity Sequence Choice: (1)
To form an unconformity, existing layers are uplifted above sea level, eroded down, subsided back underwater, and buried by new deposition.
Q6: Half-Lives Remaining Choice: (3)
100% → 50% (1 HL) → 25% (2 HL) → 12.5% (3 HL). 3 half-lives have elapsed.
NYS Earth Science Regents Answer Key: Geologic History Page 1 of 2
Part B-1 & B-2 Constructed Response Rubrics
Part B-1: Geologic Cross-Section Grading Guidance
Q7. Relative age of Intrusion H vs Layer C [2 points]
Acceptable Responses (for full 2 points):
