Science came to play a leading role in Enlightenment discourse and thought. Many Enlightenment writers and thinkers had backgrounds in the sciences and associated scientific advancement with the overthrow of religion and traditional authority in favour of the development of free speech and thought. Scientific progress during the Enlightenment included the discovery of carbon dioxide (fixed air) by the chemist Joseph Black, the argument for deep time by the geologist James Hutton, and the invention of the steam engine by James Watt. The experiments of Lavoisier were used to create the first modern chemical plants in Paris, and the experiments of the Montgolfier Brothers enabled them to launch the first manned flight in a hot-air balloon on 21 November 1783, from the Château de la Muette, near the Bois de Boulogne.

Many Enlightenment writers and thinkers had backgrounds in the sciences and associated scientific advancement with overthrow of religion and traditional authority in favor of what?