Question

read the passage and answer the following question(s).
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.
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.

Explanation:

• For option A: According to the principle of superposition in geology (younger layers are deposited on top of older ones), Layer 1 is below Layer 3, so Layer 1 is older.
• For option B: Layer 8 is above Layer 7. By the superposition principle, Layer 7 is older than Layer 8.
• For option C: There is no information in the diagram about the age comparison between Layer 3 and 400 - million - year - old rocks.
• For option D: Layer 10 is above Layer 6. By the superposition principle, Layer 6 is older than Layer 10.
• For option E: The number of fossils does not directly determine the age of a layer. The age is mainly determined by the position (superposition) and radiometric dating (not related to fossil quantity here).

Answer:

A. Layer 1 is older than Layer 3 because it is farther down.