Nicholas Steno proposed this in the 17th century and used it to derive his Law of Original Horizontality. In quantum theory, this principle led to the creation of Schrodinger's cat, because the cat must be in all states possible, alive and dead. It also is the reason interference occurs between 2 waves, as their interaction results in their addition or destruction. FTP, name this principle, which 
Nicholas Steno proposed this in the 17th century and used it to derive his Law of Original Horizontality. In quantum theory, this principle led to the creation of Schrodinger's cat, because the cat must be in all states possible, alive and dead. It also is the reason interference occurs between 2 waves, as their interaction results in their addition or destruction. FTP, name this principle, which in earth science says that the age of layers of earth gets younger as you head towards the surface.
Nicholas Steno proposed this in the 17th century and used it to derive his Law of Original Horizontality.
{superposition} or {Law of Superposition}