Final answer:
To determine the relative ages of rock layers and faults, geologists apply principles such as the Law of Superposition, Original Horizontality, and the Principle of Cross-Cutting Relationships. Folding and faulting postdate the formation of the rock layers they affect. Radiometric dating complements relative dating by providing absolute ages.
Step-by-step explanation:
Understanding Relative Dating and Rock Layers
To determine the relative ages of rock layers and a fault, geologists use several principles of relative dating. The first is the Law of Superposition, which indicates that in undisturbed horizontal sedimentary rock layers, the oldest layer is at the bottom and the youngest at the top. Observing a cross-section of rock layers, one can apply this principle to establish the order in which the layers were deposited over time. Original Horizontality suggests that layers of sediment were originally deposited horizontally. Therefore, any tilting or folding must have occurred after the rock layers were formed. This principle can guide the understanding of geological events that have affected the strata after deposition. Lateral Continuity states that layers of sedimentary rock are continuous across space until they thin out or are truncated by other geological structures, such as faults or igneous intrusions.
In Figure 3, you can identify a fault within the rock layers. According to the Principle of Cross-Cutting Relationships, the fault is younger than all the layers it disrupts. This principle helps in determining that the fault occurred after the formation of even the youngest rock layer it cuts through. If a fault is using by arrows showing sense of motion, it can be categorized as a particular type, like a normal or reverse fault, which also gives clues to the geological forces at play at the time of the faulting. When considering unconformities, like angular unconformities, it's evident that an erosional event occurred before subsequent layers were deposited. For precise dating, geologists use techniques such as radiometric dating to find the absolute age of rocks with radioactive decay providing a clock for timing. While relative dating helps determine the sequence of events and layers, absolute dating provides a numerical age. Combining both methods enables geologists to construct a comprehensive history of Earth's geological timeline.