Final answer:
Steno's three principles in geology are superposition, original horizontality, and lateral continuity. They help determine the relative ages and geological history of rocks.
Step-by-step explanation:
The three principles established by Nicolas Steno in geology are superposition, original horizontality, and lateral continuity. Superposition states that in undisturbed layers of sedimentary rocks, the oldest rock layer is at the bottom and the youngest is at the top. Original horizontality states that layers of sediment are originally deposited horizontally. Lateral continuity states that layers of sedimentary rock are continuous, and any interruption, like a river or canyon, occurred after the rock formation.
Each of these principles is important because they provide valuable information for geologists to understand the relative ages and geological history of rocks. Superposition helps determine the order in which layers were deposited, allowing for the identification of older and younger rocks. Original horizontality helps determine if there has been any tilting or folding of the rock layers since their deposition. Lateral continuity helps establish connections between rock formations and identify any disruptions that occurred after the rock formation.