Lavoisier's discovery that air was not a substance but rather a mixture of nitrogen and oxygen is described as history-making. why do you think this description is accurate?

Antoine Lavoisier was part of a wealthy family in Paris. He pursued to study science upon realizing that chemistry or the study of the elements was not a well-studied field. His discovery of that air was a mixture of nitrogen and oxygen gave rise to the concept of COMBUSTION after repeating the experiments made by Priestly using mercury and other metal oxides. 

The event was such a history-making because it disproved that concept that air was a pure substance along with 3 others: earth, fire, and water.