The chemical revolution was a period in the 18th century marked by significant advancements in the theory and practice of chemistry. Despite the maturity of most of the sciences during the scientific revolution, by the mid-18th century chemistry had yet to outline a systematic framework or theoretical doctrine. Elements of alchemy still permeated the study of chemistry, and the belief that the natural world was composed of the classical elements of earth, water, air and fire remained prevalent.[84] The key achievement of the chemical revolution has traditionally been viewed as the abandonment of phlogiston theory in favour of Antoine Lavoisier's oxygen theory of combustion;[85] however, more recent studies attribute a wider range of factors as contributing forces behind the chemical revolution.[86]