Question

in which situation is the principle of cross - cutting relationships useful in determining relative age?
a fault breaks through sedimentary layers.
fossils of two different species are found in different rock layers.
sedimentary layers form over millions of years in a lake bottom.
lava flows form on top of one another from several eruptions over time.

Explanation:

The principle of cross - cutting relationships states that a geologic feature which cuts through another is the younger of the two features. A fault is a geologic feature. If a fault breaks through sedimentary layers, we can use the principle of cross - cutting relationships. The fault is younger than the sedimentary layers it cuts through.
Fossils in different rock layers use the principle of fossil succession. Sedimentary layers forming over time use the principle of superposition (younger layers on top of older ones). Lava flows on top of one another also use the principle of superposition.

Answer:

A. A fault breaks through sedimentary layers.