In the 19th century, this was the era for which weaponry as well as mobile vehicles were being made. Tanks were starting to be made by the army for WWI and WWII. The first car, Model-T, was created by Henry Ford. This changed life as it was a personal transport rather than a train.
The correct answer is the superposition principle
The superposition principle is a principle in Geology, wherein it states that expressing that in any undisturbed arrangement of rocks stored in layers, the most youthful layer is to finish everything and the most established on base, each layer being more youthful than the one underneath it and more older than the one above it.