Question
Dating Rock Strata
Scientists can determine the age of rock layers by measuring radioactive elements within the rock. Radioactive elements found in sedimentary rocks decay quickly, so this method can only date sedimentary rocks that are less than 50,000 years old. Volcanic rock contains radioactive elements that decay very slowly, so scientists can date volcanic rocks that are much older than 50,000 years.
A team of scientists is investigating a rock formation found in a region. The diagram shows the rock formation that the scientists are investigating.
The diagram shows 10 rock layers; from bottom to top, layer 1 is sedimentary rock, layer 2 is 550 million-year-old volcanic rock, layer 3 is sedimentary rock with two trilobite fossils, layer 4 is 400 million-year-old volcanic rock, layer 5 is sedimentary rock with one trilobite fossil, layer 6 is sedimentary rock with two trilobite fossils, layer 7 is 240 million-year-old volcanic rock, layers 8, 9, and 10 are sedimentary rock.
Multiple Select Question
Which TWO statements correctly compare the rock layers?
A.
Layer 1 is older than Layer 3 because it is farther down.
B.
Layer 8 is older than 240 million years old because it is above Layer 7.
C.
Layer 3 is older than 400 million years old because it is below Layer 4.
D.
Layer 10 is older than Layer 6 because it has fewer fossils.
E.
Layer 6 is older than Layer 7 because it has more fossils.
Scientists can determine the age of rock layers by measuring radioactive elements within the rock. Radioactive elements found in sedimentary rocks decay quickly, so this method can only date sedimentary rocks that are less than 50,000 years old. Volcanic rock contains radioactive elements that decay very slowly, so scientists can date volcanic rocks that are much older than 50,000 years.
A team of scientists is investigating a rock formation found in a region. The diagram shows the rock formation that the scientists are investigating.
The diagram shows 10 rock layers; from bottom to top, layer 1 is sedimentary rock, layer 2 is 550 million-year-old volcanic rock, layer 3 is sedimentary rock with two trilobite fossils, layer 4 is 400 million-year-old volcanic rock, layer 5 is sedimentary rock with one trilobite fossil, layer 6 is sedimentary rock with two trilobite fossils, layer 7 is 240 million-year-old volcanic rock, layers 8, 9, and 10 are sedimentary rock.
Multiple Select Question
Which TWO statements correctly compare the rock layers?
A.
Layer 1 is older than Layer 3 because it is farther down.
B.
Layer 8 is older than 240 million years old because it is above Layer 7.
C.
Layer 3 is older than 400 million years old because it is below Layer 4.
D.
Layer 10 is older than Layer 6 because it has fewer fossils.
E.
Layer 6 is older than Layer 7 because it has more fossils.
Answers
GPT-5 mini
Correct answers: A and C.
- A is correct: Law of superposition—layer 1 lies below layer 3, so layer 1 is older.
- C is correct: layer 3 lies below the 400‑million‑year‑old layer 4, so layer 3 must be older than 400 million years.
The others are wrong because being above a dated layer makes a layer younger (B), fossil counts don't determine age and layer 10 is actually younger than layer 6 (D), and although layer 6 is older than layer 7, the given reason (more fossils) is not a valid basis for age (E).
- A is correct: Law of superposition—layer 1 lies below layer 3, so layer 1 is older.
- C is correct: layer 3 lies below the 400‑million‑year‑old layer 4, so layer 3 must be older than 400 million years.
The others are wrong because being above a dated layer makes a layer younger (B), fossil counts don't determine age and layer 10 is actually younger than layer 6 (D), and although layer 6 is older than layer 7, the given reason (more fossils) is not a valid basis for age (E).